Technical Program

Overcoming the long-standing strength–ductility trade-off remains a challenge in structural metals, particularly in titanium alloys where limited deformation modes constrain plasticity. Here we report a coherent bimodal structure architecture in Ti-6Al-4V. It is revealed that coherent primary α grains form on prior b grain boundaries and promote nanotwinned α variants during intercritical quenching. Such coherent bimodal structure generates strong hetero-deformation induced stresses that sequentially activate 〈a〉 dislocation slip, stacking faults, deformation twinning and 〈c+a〉 dislocation slip. These coordinated mechanisms sustain high strain hardening and enable the alloy to achieve an ultimate tensile strength of 1330 MPa and a tensile ductility of 20%, substantially outperforming this alloys with martensitic or bimodal microstructures. The present paradigm provides a new microstructural design strategy for high-performance structural alloys.

While heterostructured materials exhibit unprecedented strength-ductility synergy, their potential in governing extreme very-high-cycle fatigue (VHCF) regimes remains underexplored. This study demonstrates an order-of-magnitude VHCF life extension in bearing steels by introducing a spatially targeted heterostructure to manage local damage initiation. Moving beyond traditional inclusion control, a multi-step phase transformation is employed to embed finely dispersed bainite sheaves into a brittle martensitic matrix. By tailoring the scale of these soft, strain-accommodating domains to match the characteristic Fine Granular Area (FGA), we effectively reconstruct the micromechanical environment around inclusions. Under cyclic loading, this dual-phase heterogeneity drives active strain partitioning. Multi-scale characterization and crystal plasticity simulations reveal that the bainite domains promote hetero-deformation compatibility, acting as buffers that mitigate strain localization within the martensite. Consequently, this architecture enlarges the FGA and elevates the L10 fatigue life by 11-fold under identical inclusion conditions. This work highlights the critical role of local heterostructure design in delaying fatigue damage, offering a new paradigm for high-strength alloys.

Cu–Zn alloy bars were subjected to various cold-rolling routes to investigate the evolution of heterogeneous nanostructure (HN-structure) and their mechanical responses. Three rolling processes were employed; (i) simple unidirectional rolling (1DR), (ii) rolling process in which specimen is rotated at 25% reduction once for 90°along rolling direction (1RR), and (iii) rolling process in which specimen is rotated at 12.5%, 25% and 37.5% reductions each for 90 ° along rolling direction (3RR). All specimens were subsequently rolled to a final reduction of 90%.After cold rolling, complex HN-structures, comprising deformation-induced structures, such as “eye-shaped” twin domains, ultra-fine lamellae and shear bands, were well developed in all specimens regardless of rolling routes. The volume fraction of twin domains increased with the number of 90°-rotations. Tensile tests of the specimens revealed that both strength and strain-hardening capability increased with increasing volume fraction of the twin domain.Digital image correlation analyses of the specimens during the tensile deformation showed the highly inhomogeneous strain distribution in HN-structured specimens; tensile strain was strongly localized within the shear bands, whereas twin domains exhibited relatively lower strain values. Loading–unloading–reloading cyclic tests revealed that hetero-deformation-induced (HDI) stress made a significant contribution to increase the overall flow stress, and its magnitude increased with the volume fraction of twin domains.These findings suggest that mechanical incompatibility between “harder” twin domains and the surrounding “softer” components plays one of key roles in enhancing the mechanical properties of HN-structure through the HDI strengthening mechanism.

This study presents an alternative approach for fabricating Ni-based harmonic structures via electroless plating, instead of the conventional mechanical milling route. Electroless Ni-plated powders were successfully consolidated by spark plasma sintering (SPS) at 1023 K and 1073 K. SEM observations revealed that the sample sintered at 1023 K consisted of coarse-grained Ni domains embedded within a fine-grained Ni–Ni₃P matrix, forming a conventional harmonic structure, hereafter referred to as Harmonic Structure Type 1 (HS Type 1). In contrast, the sample sintered at 1073 K exhibited a predominantly coarse-grained microstructure; however, EDS analysis confirmed the presence of an interconnected phosphorus-enriched network, resulting in a harmonic-like structure designated as Harmonic Structure Type 2 (HS Type 2). Both sintered samples exhibited improved 0.2% proof strength and ultimate tensile strength (UTS) compared with the initial powder (IP) Ni. Tensile testing demonstrated that HS Type 1 achieved superior strength owing to the combined effects of harmonic structure design and Ni–Ni₃P strengthening, with the finely dispersed Ni₃P particles effectively impeding crack propagation. Meanwhile, HS Type 2 exhibited moderate strengthening with minimal loss of ductility relative to IP Ni. This improved mechanical performance was attributed to phosphorus-induced solid-solution strengthening and the formation of an interconnected phosphorus-enriched hard-region network, both of which contributed to enhanced hetero-deformation-induced (HDI) strengthening. These findings demonstrate that deposition layer thickness and sintering temperature can effectively tailor the microstructure and mechanical performance of Ni-based harmonic-structure materials fabricated via electroless Ni plating.

Metallic materials with uniform microstructures have a trade-off relationship between strength and ductility. A larger grain size leads to higher ductility, but a smaller grain size leads to higher strength. To solve this problem, "harmonic structure control" is attracting attention. This method designs heterostructured materials. These materials have a network region of fine grains and a dispersed region of coarse grains. They achieve an excellent balance of strength and ductility by the synergy effect of the two regions. However, conventional harmonic structures do not always achieve both high strength and high ductility. When the size difference between fine and coarse grains is too large, it is difficult to improve both properties at the same time. Therefore, it is necessary to design a new grain size distribution that includes a medium grain region. In this study, a "tri-modal harmonic structure" with pure Ni was designed. This structure consists of three grain size regions: fine, medium, and coarse. The compacts were fabricated by mechanical milling (MM) and spark plasma sintering (SPS) at 1173 K. Room-temperature tensile tests and microstructural observations using a scanning electron microscope (SEM) were performed. The results showed that controlling the fraction of the medium grain region is very important. Forming a tri-modal grain distribution contributes significantly to achieving both high strength and high ductility.

Steel can exhibit a wide range of microstructures, including ferrite, bainite, and martensite, depending on alloy composition and processing conditions. This versatility enables steels to achieve a broad spectrum of mechanical properties, making them one of the most widely used structural materials. Through advances in microstructural control, numerous steel grades have been developed, and steel has become a fundamental material supporting modern society.In recent years, societal demands such as lightweighting, extreme service environments, and carbon neutrality have increased significantly. Accordingly, steels are required to simultaneously achieve higher strength and toughness, improved resistance to hydrogen embrittlement, and low-alloy design for recyclability. To meet these complex requirements, new microstructural control strategies are needed.This work proposes a new approach based on chemical heterogeneity. While conventional steel design relies on chemically homogeneous compositions, controlled heterogeneity can provide greater flexibility in microstructural design. Local compositional variations enable control of phase transformation kinetics and allow tailoring of phase fraction, morphology, and spatial distribution. Furthermore, this approach can enhance mechanical properties while reducing alloying content.In this presentation, a microstructural control strategy based on chemical heterogeneity will be introduced, along with case studies demonstrating improved microstructures and mechanical properties in high-strength steels. Future research directions and potential applications will also be discussed.

Additive manufacturing enables microstructural control through localized thermal-history manipulation, yet the mechanistic origin of as-deposited strengthening in low-Mn, ferrite-based Fe-Mn-Al-C lightweight steels remains unresolved. Here, we clarify how specific laser energy input (Esp) controls microstructural evolution and tensile response in a low-Mn Fe-Mn-Al-C triplex steel fabricated by directed energy deposition. Reducing Esp refines the intercellular/interdendritic topology and enhances microchemical heterogeneity, producing an Al-enriched ferritic matrix and a C/Mn-enriched martensite/austenite (M/A) constituent. Near-atomic-scale characterization shows that the dominant build-to-build chemical difference is stronger C partitioning to the M/A constituent and larger local C segregation amplitudes in the lower-Esp build, while Mn contributes mainly through interfacial enrichment. High-resolution transmission electron microscopy further reveals ~2.5 nm FeAl-type B2-ordered domains in ferrite, with higher domain density and stronger ordering at lower Esp. During early deformation, this B2-richer ferrite develops more planar slip and paired dislocation contrasts consistent with shearing of ordered regions, whereas the higher-Esp condition exhibits wavier, more spatially distributed ferrite deformation. These chemical and micromechanical differences govern the strain-resolved transformation kinetics of retained austenite: the lower-Esp build shows delayed but stronger transformation-induced plasticity (TRIP), while the higher-Esp build transforms earlier and becomes progressively exhausted. Consequently, the lower-Esp condition achieves an as-deposited ultimate tensile strength above ~1.0 GPa without post-deposition heat treatment. These findings show that thermal-history-mediated solute, redistribution can couple nanoscale ferrite ordering with strain-dependent TRIP, offering a mechanistic strategy for designing high-strength as-deposited heterogeneous lightweight steels.

A finite element modeling framework was developed and validated to predict the anisotropic mechanical behavior and formability of linear friction welded dual-phase steel. A multiscale material model comprising a ductile damage criterion for bulk anisotropic plasticity and a cohesive zone model to represent interface behavior was initially calibrated and validated using uniaxial tensile test data, acquired from both the through-thickness and width directions of the welded joint. The calibrated parameters were then successfully applied to simulate a sheet forming operation, confirming the model's transferability to complex deformation modes governed by stress triaxiality. Numerical predictions were rigorously assessed against a comprehensive set of experimental measurements. The results demonstrated that the proposed combination of multiscale modeling for dissimilar material regions and finite element simulation of forming accurately captured the direction-dependent strength, ductility, and fracture characteristics of the welded steel. Furthermore, the forming simulation showed good agreement with experimentally observed forming limits and strain localization patterns. Collectively, this work establishes a practical, microstructure-informed simulation tool that connects the linear friction welding process to the resulting anisotropic constitutive response and final formability, thereby facilitating the optimized design of lightweight welded blanks for automotive applications.

In this study, two Incoloy 825/API X65 multilayer clad plates were fabricated by hot rolling: one at a finish rolling temperature of 1050 ℃, above the non-recrystallization temperature of API X65 steel (FT1050) and the other at 825 ℃, below Tnr (FT825). Compared to the FT1050 plate, the FT825 plate exhibited a thicker decarburized layer and finer grains in API X65 steel, as well as a thicker carburized layer and larger γ grains in Incoloy 825 alloy. Both plates showed same thickness with 7 μm γ-fcc interfacial layer containing interfacial oxides. In addition, Cr diffused farther than Ni from Incoloy 825 into API X65 steel at the interfacial layer, due to its higher diffusivity, despite steeper Ni concentration gradients. Meanwhile, the FT825 plate exhibited superior shear strength and displacement, with fracture propagating across both the interfacial and decarburized layers of API X65 steel. On the other hand, the FT1050 plate fractured primarily along the interfacial layer. This difference in fracture behavior is attributed to variations in interfacial oxides. In the FT1050 plate, interfacial oxides were larger and more elongated, while in the FT825 plate, they were finer and more numerous. The finely interfacial oxides contributed to dispersion strengthening of the interfacial layer. In addition, they promoted competitive cracking between the interfacial layer and the decarburized layer, thereby improving the shear properties of the hot-rolled Incoloy 825/API X65 multilayer clad plate.

Nanoporous gold (NPG) is a nanoscale open-cell metallic material with low density and high specific surface area, making it attractive for applications in sensors, actuators, and catalysts. However, its intrinsic brittleness and low tensile reliability under tensile loading remain major limitations for practical use. In conventional bulk metallic materials, reducing grain size can enhance strength through the Hall–Petch relationship. In this study, we investigated the effect of internal microstructural control on the mechanical properties of NPG.Three types of NPG specimens were fabricated by free-corrosion dealloying from Ag–Au precursor alloys: a nanocrystalline precursor alloy, a heat-treated precursor alloy with coarsened grains, and a heat-treated precursor alloy with increased dislocation density. The microstructures of the resulting NPG specimens were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). Their mechanical properties were evaluated by nanoindentation and three-point bending tests.The nanoindentation results showed that the hardness of NPG was not significantly affected by the internal microstructure. In contrast, the bending strength of nanocrystalline NPG was approximately 33% lower than that of coarse-grained NPG. These results indicate that grain refinement does not necessarily improve the mechanical reliability of nanoporous gold, and that microstructural features such as grain boundaries and defect structures should be carefully considered when designing mechanically robust NPG.

Selective electron beam melting (SEBM) inherently produces a spatially heterogeneous microstructure in high γ′ nickel based superalloys, in which strongly textured columnar grains coexist with a build height dependent gradient in γ′ size and fraction. Understanding how this heterostructure governs strengthening mechanisms is essential for turbine applications. Here a cost reduced and weldable 247 type superalloy, CW247, was designed from CM247LC by combining Thermo Calc screening with density functional theory derived γ′ planar fault energies. From 36,450 candidate compositions, CW247 was obtained by lowering Al, Ta, W, and segregation prone minor elements while increasing Ti and adding Nb to raise the planar fault energy of γ′ and shearing resistance. The alloy was fabricated by SEBM into a dense specimen exceeding 80 mm in height, with a relative density of 99.8% and a crack area fraction of about 0.07%, developing ⟨001⟩ textured columnar grains and a γ′ gradient that confirm its hierarchically heterogeneous architecture. Despite a reduced γ′ fraction, CW247 retained about 97% of room temperature yield strength at 871 °C, and the HIP treated alloy reached a creep rupture life of about 333 h at 815 °C and 448 MPa, comparable to MAR M247. Post deformation STEM revealed isolated stacking faults, intersecting faults from Lomer Cottrell locking, and limited APB coupled shearing, indicating that continuous planar fault propagation within γ′ was effectively restricted. Together with reduced Ta and Hf, these mechanisms give CW247 a favorable balance of high temperature strength, creep resistance, and raw material price competitiveness.

High-temperature deformation is widely used to tailor the microstructural and mechanical properties of metallic materials. Since microstructure and mechanical behavior are strongly interrelated, one can often be interpreted from the other. Conventional structure–property correlations generally compare only the initial and final states of a material, overlooking important intermediate microstructural evolution that is critical for accurate process optimization and industrial control. In this study, an excellent balance of strength and ductility was achieved in a high-strength Al 7XXX alloy (Zn/Mg ratio: 2.9–4.4) through extreme plastic deformation followed by artificial aging. The alloy exhibited a peak tensile strength of ~700 MPa with ~20% elongation. The enhanced strength originated from a refined distribution of nano-sized η′ and η precipitates, while the improved ductility was attributed to enhanced work hardening induced by these precipitates.

Achieving a superior combination of strength, ductility, and electrical conductivity remains a major challenge for Cu alloys, because conventional strengthening strategies usually lead to significant losses in plasticity or conductivity. In this work, a heterostructured Cu-0.1Sn alloy was fabricated using dynamic-offsets and shear-force-adjustment cryorolling (DSCR) followed by annealing. The DSCR process introduces severe plastic deformation, additional shear strain, high-density dislocations, and refined lamellar structures, while subsequent annealing promoted partial recrystallization and defect recovery. As a result, a typical heterostructure consisting of recrystallized coarse-grained soft domains and lamellar non-recrystallized hard domains was successfully constructed.The heterostructured Cu-0.1Sn alloy annealed at 598 K exhibited a favorable balance of mechanical and functional properties. At room temperature, the alloy achieved an ultimate tensile strength of 401 MPa, a uniform elongation of 11.1%, and a high electrical conductivity of 87.6% IACS. More importantly, when deformed at 77 K, both strength and ductility were simultaneously enhanced, reaching an ultimate tensile strength of 510 MPa and a uniform elongation of 28.1%. Microstructural characterization and loading-unloading-reloading tests indicated that the excellent mechanical response was mainly attributed to strain partitioning between soft and hard domains, geometrically necessary dislocation accumulation near hetero-interfaces, and cryogenic-enhanced hetero-deformation-induced hardening. These results demonstrate that DSCR combined with annealing is an effective strategy for constructing heterostructured Cu alloys with balanced strength, ductility, and electrical conductivity.

AlCoFeNi2 and AlCoCrFeNi2 alloys, classified as eutectic high-entropy alloys, are composed of body-centered cubic (BCC) and face-centered cubic (FCC) phases. However, the relationship between the microstructure and mechanical properties of these alloys fabricated by the powder metallurgy (PM) process remains unclear. In this study, AlCoFeNi2 and AlCoCrFeNi2 alloys were fabricated via spark plasma sintering (SPS) using gas-atomized powders, and their microstructures and mechanical properties were investigated in detail. Sintering was performed at 1173, 1273, and 1373 K. Mechanical properties were evaluated by tensile tests at room temperature. Microstructural observation was performed using scanning electron microscopy, electron backscatter diffraction (EBSD), and energy-dispersive X-ray spectroscopy. Both AlCoFeNi2 and AlCoCrFeNi2 compacts consist of lamellar grains with layered FCC/BCC structures and equiaxed grains containing a mixture of FCC and BCC phases. The FCC to BCC area ratio is approximately 1:1 for AlCoFeNi2, whereas it increases to roughly 2:1 for AlCoCrFeNi2. While increasing the sintering temperature for the AlCoCrFeNi2 alloy decreased strength but improved ductility, it simultaneously enhanced both strength and ductility in the AlCoFeNi2 alloy. EBSD analysis reveals that regions with high dislocation density correspond to the FCC phase, indicating preferential plastic deformation. Additionally, observation near the fracture surface suggests that cracks initiate at the FCC/BCC interface.

Gradient nanotwinned (GNT) metals exhibit superior mechanical properties compared to their uniform counterparts, yet the underlying deformation mechanisms remain poorly understood. This study employs discrete dislocation dynamics simulations to investigate the microstructural evolution and mechanical response of GNT copper structures. Prior to examining gradient structures, the size dependence of multilayer twin structures was systematically analyzed through twin thickness (40–320 nm) and grain size variations. Three characteristic loading orientations were considered: perpendicular, parallel, and 45° inclined to twin boundaries. Confined slip models and dislocation pile-up theory were developed to describe the strengthening behavior, with particular attention to the role of twin boundary defects in promoting dislocation absorption and hardening. Building upon these findings, three GNT architectures were constructed with varying twin thickness gradients: GNT-1 (low gradient, 8A-4B-2C), GNT-2 (high gradient, 2(4A-2B-1C)), and GNT-3 (sandwich gradient, 4A-2B-2C-2B-4A), where A, B, and C represent twin thicknesses of 40, 80, and 160 nm, respectively. Uniform nanotwinned (UNT) structures with equivalent compositions served as reference materials. Simulation results demonstrate that GNT structures generally obey the rule of mixtures, with flow stresses comparable to the volume-weighted average of constituent layers. However, gradient configurations with pronounced thickness variations exhibit enhanced confined slip due to increased twin boundary defect density, enabling strength levels approaching those of the strongest uniform component. The absence of additional strengthening beyond the rule of mixtures suggests that the superior properties reported in experimental gradient nanotwinned metals may originate from higher dislocation densities and interface nucleation mechanisms not captured in the present simulations.

Heterostructure design is a promising materials design strategy that can simultaneously enhance strength and ductility through the hetero-deformation induced strengthening effect. In this study, a compositional heterostructure was designed in an Fe-based medium-entropy alloy, introducing the concept of spatial metastability control (SMC). Pure Fe powders were integrated into metastable MEA powders, establishing a phase stability gradient across the MEA/Fe interface. To achieve this, metastable medium-entropy alloy powders were mixed with pure Fe powders, followed by high-pressure torsion processing and post-annealing. The multi-material structure exhibited sound bonding and compositional gradients at the interphase. This gradient formed a distinct transition region characterized by refined grain size, thermal martensite formation, and moderate solid solution strengthening. The SMC specimen achieved an outstanding strength–ductility combination at both room and cryogenic temperatures through sequential transformation-induced plasticity (TRIP) behavior, with was more active than the TRIP behavior of the single-material counterpart, thereby demonstrating the effectiveness of the spatial metastability control strategy. This design framework offers a versatile pathway for developing heterogeneous materials with tunable mechanical performance through spatial control of phase stability across a broad temperature range.

Growing interest in space exploration and liquid hydrogen (LH₂)-based energy systems has created an increasing demand for structural materials capable of reliable operation under cryogenic environments. Face-centered cubic medium-entropy alloys (MEAs) are regarded as promising candidates for such cryogenic applications because of their excellent mechanical properties and high fracture resistance at low temperatures. However, conventional CoCrNi-based MEAs exhibit relatively low yield strength, and the abrupt stress fluctuations associated with discontinuous plastic flow below approximately 20 K highlight the need to improve their mechanical stability for practical structural applications. In this study, Al and Ti were added to a CoCrNi-based MEA to induce L1₂ precipitation, and the tensile properties and fracture toughness of the fabricated alloy were evaluated at 4.2 K. Microstructural analysis revealed that the L1₂ MEA exhibited a heterogeneous necklace-like microstructure, in which fine grains surrounded coarse grains. Tensile testing at 4.2 K showed that the L1₂ MEA had a markedly enhanced yield strength compared with the equiatomic CoCrNi alloy, while exhibiting a relatively reduced serration amplitude. In addition, the KJIc value measured at 4.2 K exceeded 300 MPa·m1/2, which is nearly twice that of austenitic stainless steel 304L, indicating superior fracture toughness compared with austenitic stainless steels commonly used in cryogenic applications. The deformation and fracture behavior of the L1₂ MEA were further examined based on microstructural observations of the specimens subjected to tensile and fracture toughness testing.

L12 precipitation-strengthened medium-entropy alloys (MEAs) have emerged as promising candidates for overcoming the conventional strength-ductility trade-off. However, many reported MEAs rely on a high Co content to stabilize the FCC matrix and L12 precipitates, compromising cost and weight efficiency required for practical structural applications. Co-free design is therefore attractive, but the absence of Co can promote brittle precipitate, including η phase, leading to ductility loss. Thus, controlling precipitate formation and evolution is essential for realizing high-performance Co-free precipitation-strengthened MEAs. To address this challenge, a Co-free Fe40Mn15Ni35Al5Ti5 MEA was designed and processed through cold rolling, short-time annealing, and subsequent aging. This thermomechanical route established a hierarchical heterostructure by tailoring grain-scale and precipitate-scale heterogeneity, while simultaneously regulating precipitate evolution and interfacial characteristics. The resulting architecture enabled multiscale precipitation strengthening and hetero-deformation-induced hardening, achieving a yield strength of 1043 MPa, an ultimate tensile strength of 1448 MPa, and a total elongation of 22%. This study suggests that integrating heterostructure design with precipitate and interface control offers an effective strategy for developing high-strength, ductile Co-free MEAs.

In this study, high-pressure torsion processing was applied to face-centered cubic (fcc) CoCrNi and body-centered cubic (bcc) NbTiZr, two representative equiatomic medium-entropy alloys (MEAs) with different crystal structures. The formation of nanocrystalline (NC) structures was confirmed in both MEAs by transmission electron microscopy. Nanoindentation tests were performed on the coarse-grained and NC specimens to estimate hardness, strain-rate sensitivity, and pile-up ratio. In addition, following hydrogen charging, nanoindentation and thermal desorption analysis were performed to investigate the effect of hydrogen on the mechanical behavior of the fcc and bcc MEAs.

Ti-6Al-4V exhibits high specific strength, but its low hardness and poor wear resistance limit its use in tribological environments. Integrating Ti-6Al-4V with a high-entropy alloy (HEA) higher hardness and excellent wear resistance provide a feasible process to overcome these limitations while retaining tribological accommodation properties. In this study, Ti-6Al-4V and AlTiCrV0.5Fe0.5 HEA heterogeneous multilayers were prepared by alternately stacking the two powders followed by spark plasma sintering (SPS) process. The SPS process enabled the effective fabrication of dense multilayered structures with alternating Ti-6Al-4V and HEA layers by simultaneously promoting powder densification and interfacial diffusion bonding under rapid heating and applied pressure. This multilayered design provides a structural advantage by combining the deformation accommodation capability of Ti-6Al-4V with the high hardness and wear resistance of the HEA layers. Since sliding in practical applications can occur in various directions relative to the multilayer interfaces, wear behavior was investigated as a function of sliding direction to evaluate interfacial stability and complex wear mechanisms caused by the simultaneous friction of dissimilar materials. No interfacial delamination was observed during wear testing, indicating strong interfacial bonding. These results suggest that Ti-6Al-4V/HEA heterogeneous multilayers can serve as HEA-based hybrid structural materials for tribological applications requiring both specific strength and wear resistance.

Overcoming the strength-ductility trade-off in Co-rich CoNiV medium-entropy alloys (MEAs) through heterostructure engineering was systematically investigated. Firstly, nonequiatomic Co70Ni20V10 and Co65Ni20V15​ MEAs were designed to reveal the synergistic effects of dislocation slip, HCP martensitic transformation, and chemical short/medium-range orders (CSRO/CMRO). The Co65Ni20V15​​ MEA exhibited an abnormally higher strain-hardening rate despite lower dislocation density, attributed to profound CSRO/CMRO strengthening. Secondly, a Co60Ni20V20​N0.3​ MEA was developed to tailor heterogeneous architectures via annealing. Compared to the brittle fully-recrystallized state (1000°C), annealing at 800°C and 900°C simultaneously enhanced strength and ductility. The 900°C annealed sample developed heterogeneous lamellae comprising HCP, LPSO 9R, and 12R structures. The 800°C annealed sample exhibited a unique architecture: nano-L12​ precipitates within grains, 9R structures, and ductile precipitation-free FCC zones near grain boundaries due to segregation, enabling ultrahigh strain-hardening (~10 GPa). These strategies provide guildlines of architecturing heterogeneous structures effectively for superior mechanical performance.

As a type of heterostructure material, multilayer materials have attracted widespread research interest due to excellent mechanical properties and high design flexibility. Typical preparation processes of multilayer materials, such as roll-bonding and sintering of rolled sheets, inevitably lead to the formation of strong crystallographic texture. In hexagonal close-packed metals the activation of different twinning and slip systems is strongly dependent on crystallographic texture, but its role in the deformation of multilayer materials has received limited attention. In this study, Ti/Ti6Al4V multilayers were fabricated by spark plasma sintering from rolled sheets to investigate how texture affects the influence of hard interfacial layers on the deformation behavior of pure Ti. The microstructural evolution of multilayer materials during tensile deformation was tracked using quasi-in-situ electron backscatter diffraction. Twin boundary statistics and slip trace analysis reveal that hard interfacial layers suppress the formation of compression twins and sustain activation of prismatic multiple slip when loading along the rolling direction, allowing the multilayer material to achieve enhanced strength while maintaining good ductility compared with pure Ti. When loading along the transverse direction, limited activation of prismatic slip restricts the effect of hard interfacial layers on work hardening, while also promoting the formation of tension twins, resulting in deterioration of ductility despite strength enhancement. This is attributed to the varying interactions between the hard interfacial layers and different deformation mechanisms. The findings provide insights on deformation of constrained Ti and offer guidance for design of multilayer materials by control of texture.

The design of high-entropy alloys (HEAs) often introduces intermetallic phases, which typically result in ductility loss or even embrittlement due to their inherent brittleness. Optimizing the high hardness of brittle phases while minimizing their embrittling effects is crucial for developing high-performance HEAs. This study proposes a hierarchical heterostructure strategy that utilizes the precipitation of s phases to enhance the strengthening effect of the B2 phase while minimizing its embrittlement role. Using a model material Al0.3CoCrFeNi HEA, this architecture is achieved through a high-temperature short-term annealing and intermediate temperature aging thermo-mechanical treatment. The resulting heterogeneous structure exhibits an exceptional strength-ductility combination at both room and cryogenic temperatures. This is evident in its mechanical properties with a yield strength of ~780 MPa/~1125 MPa, an ultimate tensile strength of ~1203 MPa/~1615 MPa, and a uniform elongation of ~25 %/~25 % at room and cryogenic temperatures. The spatial modulation of hierarchical co-precipitation of B2 and s phases at grain boundaries and within interiors domains effectively regulates the strain partitioning between the soft and hard regions. This microstructure induces significant hetero-deformation induced (HDI) stress and activates extensive planar defects, including hierarchical stacking faults and sparse deformation twins. The excellent strength and ductility at cryogenic temperature are associated with a synergistic factor. These include extensive deformation twins (DTs)/SFs, their multifarious planar defect deviants (e.g., hierarchical SFs/DTs networks, L-C locks) and nano-twins bundles. This work provides new routes for developing strong yet ductile structural metallic materials via introducing deformable intermetallic precipitates.

High-temperature creep deformation of additively manufactured Ti–6Al–4V is strongly affected by the initial microstructural state developed during rapid solidification and subsequent thermal exposure. In this study, selective laser melted Ti–6Al–4V with two different microstructures, an as-built α′ martensitic condition and a thermally stabilized α+β condition, was investigated under creep at 500 °C to clarify the roles of phase stability and defect evolution. Microstructural changes before and after creep were examined using EBSD, XRD, and TEM, with emphasis on dislocation rearrangement, α′ decomposition, phase-interface interactions, and internal stress relaxation. The as-built α′ condition, containing a high density of defects and metastable martensite, exhibited rapid microstructural rearrangement during creep. This caused localized deformation, interfacial instability, and accelerated creep damage accumulation. In contrast, the thermally stabilized α+β condition showed lower defect density and enhanced phase stability, promoting more uniform dislocation activity and delayed damage evolution. The β phase and α/β interfaces contributed to dislocation absorption and diffusion-assisted relaxation, thereby influencing vacancy redistribution and creep damage development. These results indicate that creep resistance in additively manufactured Ti–6Al–4V is governed not only by phase constitution, but also by the stability of defects and heterogeneous phase-interface structures. This study highlights the importance of controlling initial microstructural stability to improve the high-temperature reliability of additively manufactured titanium alloys.

Multi-principal-element alloys and advanced manufacturing provide versatile platforms for developing heterostructured metallic materials with superior mechanical properties. Here, we report that heterostructure engineering can be systematically achieved through compositional and thermal-field design, enabling simultaneous enhancement of strength and ductility. First, compositional engineering was applied to CoNiV-based multi-principal-element alloys to regulate stacking-fault energy, κ-phase stability, and local chemical order. Cr/Si-mediated tuning of κ-phase shearability and Si-enabled hierarchical heterostructure control were found to substantially influence deformation partitioning and strain accommodation. The resulting heterogeneous face-centered-cubic/κ-phase architecture promoted pronounced hetero-deformation-induced strengthening and back-stress hardening, delivering an exceptional combination of strength, ductility, and work-hardening capacity after post-heat treatment. To further enable in situ control of heterostructure formation, we developed a liquid-metal-assisted laser powder bed fusion strategy that introduces thermal-field engineering during processing. Using liquid Sn as a dynamic heat-transfer medium fundamentally alters the thermal boundary conditions, allowing controlled cooling kinetics, reduced thermal gradients, and in situ thermal modulation of deposited layers. This thermal-field engineering promotes the formation of non-equilibrium heterogeneous microstructures in stainless steel, Inconel 718, and Ti-6Al-4V alloy, including hierarchical grain structures, refined phase architectures, and graded defect networks. These heterostructures effectively sustain strain hardening and enhance the synergy between strength and ductility. Despite differences in alloy systems and processing routes, both approaches reveal a common governing principle: heterostructure-regulated strain partitioning and defect interactions can overcome the conventional strength–ductility trade-off. By coupling compositional and thermal-field strategies, this study establishes a unified framework for engineering high-performance metallic materials and offers new insights into heterostructure design.

Accurate evaluation of hot formability is essential for the reliable processing and optimization of advanced austenitic steels. However, conventional constitutive approaches often fail to fully capture complex flow behaviors in high-alloy systems, particularly under conditions exhibiting anomalous strain rate sensitivity and flow instability near the boundaries of the processing window. To address these challenges, this study evaluates the hot deformation behavior of austenitic steels using Dynamic Material Modelling (DMM), with emphasis on identifying processing domains with good hot workability and regions prone to instability.The methodology was applied to a newly developed Corrosion-Resistant Lightweight Steel (CRLS). Unlike conventional lightweight steels, this alloy contains chromium to provide corrosion resistance and exhibits unique flow behavior governed by severe Al-C solute drag. The results showed that the hot workability of CRLS strongly depended on deformation temperature and strain rate. Through microstructural characterization using Electron Backscatter Diffraction (EBSD) and Parametric Line Profile Analysis, the main flow instability mechanisms were identified as transformation-induced cracking at low strain rates and dislocation overloading at high strain rates in the low-temperature regime.To verify the broader applicability of the analysis, the same approach was also examined using commercial FXM19, a high-nitrogen austenitic stainless steel of interest for Small Modular Reactors and liquid hydrogen infrastructure. The processing map successfully captured the non-monotonic variation in peak flow stress with strain rate, indicating a region of low or negative strain rate sensitivity in the intermediate strain rate range, consistent with dynamic strain aging-type interactions reported in nitrogen-strengthened austenitic stainless steels.

Heterogeneous layered metal matrix composites (MMCs) offer a promising strategy for improving the strength–ductility–wear of stainless-steel (SS)-based structural materials. In this work, instead of uniformly mixing Y2O3 nanoparticles and graphene nanoplatelets (GNPs), their functional roles are spatially separated to develop a symmetric sandwich-type SS316L-based composite with the architecture SS316L–0.20wt.%GNP/SS316L–0.30wt.% Y2O3/SS316L–0.20 wt.% GNP via spark plasma sintering (SPS). The Y2O3-reinforced core layer is designed to promote oxide-dispersion strengthening, grain-boundary pinning, and load-bearing stability, while the GNP-reinforced outer layers are intended to enhance surface damage tolerance, reduce friction, and promote graphene-assisted tribofilm formation during sliding. The densification behavior, interfacial evolution, phase constitution, reinforcement distribution, and deformation mechanisms will be systematically investigated. This layered architecture is expected to provide a mechanism-guided pathway for achieving improved strength–ductility–wear synergy in SPS-consolidated SS316L-based hybrid composites.

Conventional cold drawing of metallic wires inevitably leads to the strength-ductility trade-off, which limits their structural applications. Heterostructured materials offer a promising solution, yet fabricating stable gradient structures under severe plastic deformation remains challenging. Here, we developed a facile pre-torsion followed by cold drawing strategy to engineer gradient grain structures (ε=1.5) and gradient lamellar structures (ε=4.0) in pure iron wires. Compared to homogeneous cold-drawn wires, the gradient grain sample exhibits a 33% increase in tensile strength (808 MPa vs. 607 MPa) and a 72% improvement in elongation (11.5% vs. 6.7%). The gradient lamellar wire achieves an ultrahigh tensile strength of 1277 MPa with a tripled uniform elongation. Mechanistically, pre-torsion introduces a radial strain gradient and high-density geometrically necessary dislocations (GNDs). Subsequent cold drawing drives continuous dynamic recrystallization via GND gliding and clustering, transforming low-angle to high-angle grain boundaries and establishing the gradient architecture. The superior mechanical properties originate from hetero-deformation induced (HDI) strengthening and hardening. This work provides a scalable approach to fabricate high-performance heterostructured wires.Keywords: Heterostructured wires; Pre-torsion; Cold drawing; Gradient microstructure; Strength-ductility synergy; Hetero-deformation induced hardeningReferences:[1] Dasheng Wei et al. Materials Characterization 171 (2021) 110821.[2] Dasheng Wei et al. Materials Letters 304 (2021) 130644.

Graphene-reinforced Cu composites are attractive for advanced structural and functional applications because of their outstanding mechanical, thermal, and electrical properties. However, conventional homogeneous and laminated graphene architectures often suffer from graphene agglomeration and pronounced property anisotropy, making three-dimensional graphene networks an increasingly attractive alternative. Herein, a powder-based strategy combining electroless Ni plating and chemical vapor deposition (CVD) was developed to fabricate a Gr/Ni/Cu metal matrix composites (MMCs) containing a quasi-three-dimensional (quasi-3D) graphene network. Despite marked microstructural differences between the in-plane and through-plane directions after hot pressing, the composite exhibited remarkably low tensile and compressive anisotropy factors of 8.2% and 0.66%, respectively. Moreover, graphene incorporation simultaneously improved tensile strength and ductility, thereby overcoming the conventional strength–ductility trade-off and achieving an elongation retention of 111.23%. The enhanced tensile performance was attributed to crack-bridging and strain-delocalization effects induced by the quasi-3D graphene network. These findings highlight the potential of the proposed electroless plating–CVD approach for developing high-performance graphene-reinforced MMCs with reduced mechanical anisotropy.

The mechanical properties of Cu–Ni–Si alloys are mainly governed by the formation and fraction of Ni2Si precipitates, which act as the primary strengthening phase, and the strength generally increases with increasing Ni and Si contents. However, an increase in solute content promotes heterogeneous nucleation at grain boundaries, resulting in the formation of coarse and irregularly shaped Ni2Si inclusions. These inclusions not only suppress the formation of fine intragranular Ni2Si precipitates but also induce stress concentration during plastic deformation, thereby deteriorating the mechanical properties. To mitigate the deterioration of mechanical properties caused by these inclusions, Mn was added to Cu–Ni–Si alloys with high Ni and Si contents, and its effects on the microstructural evolution and mechanical properties were investigated. Cu–6Ni–1.25Si and Cu–6Ni–1.25Si–2.14Mn alloys were homogenized at 980°C for 8 h and subsequently cold-rolled to different thickness reduction ratios. As a result, the Mn-added alloy exhibited higher strength after homogenization, and the degree of strength increase with increasing reduction ratio was also greater. Microstructural analysis revealed that the coarse and irregularly shaped Ni2Si inclusions formed at the grain boundaries of the Cu–6Ni–1.25Si alloy were transformed into film-like Ni16Mn6Si7 compounds upon Mn addition. This transformation of the grain-boundary phase reduced the fraction of coarse inclusions. As a result, the fraction of fine intragranular Ni₂Si precipitates relatively increased. Furthermore, the continuous film-like morphology of the Ni16Mn6Si7 compound alleviated stress concentration during plastic deformation, contributing to the overall improvement in mechanical properties.

Core–shell microstructures have attracted significant attention for breaking the strength–ductility trade-off in metallic materials. However, their fabrication has been largely confined to complex powder metallurgy routes. This study introduces a novel and scalable thermo-mechanical processing (TMP) strategy to develop an integral core–shell architecture directly within a cast Ni-rich high-entropy alloy (HEA). By utilizing strain-induced grain boundary migration (SIBM) during hot rolling, localized bulged regions were formed; these regions subsequently expanded through the growth of discontinuous L12 precipitates and were stabilized into fine-grained shells via the pinning effect of B2 and L12 precipitates during heat treatment. The remaining deformed coarse grains successfully served as the structural core. Benefiting from this unique structural heterogeneity, the developed alloy exhibited pronounced hetero-deformation-induced (HDI) strengthening and efficient strain partitioning, achieving an exceptional strain hardening rate of approximately 3.4 GPa. This work provides a cost-effective and highly scalable methodology for engineering advanced core–shell heterostructures in bulk cast HEAs for high-performance structural applications

Among high-entropy alloys (HEAs), multiphase HEAs containing intermetallic compounds exhibit excellent mechanical properties. Although the CrFeCoNiMo alloy containing intermetallic phases is expected to be a high-strength material, the relationship between its microstructural evolution and deformation behavior at elevated temperatures has not been fully clarified. Therefore, CrFeCoNiMo alloy compacts were fabricated using mechanical milling (MM) and spark plasma sintering (SPS) to investigate this correlation in detail. CrFeCoNiMo gas-atomized powder was used as the initial powder (IP), and MM was performed for 360 ks. Both IP and MM powders were consolidated via SPS at temperatures of 1273 and 1373 K under 100 MPa. X-ray diffraction revealed that the sintered compacts consisted of FCC and R phases. The MM compacts possessed a finer crystalline grain structure than the IP compacts. For both compacts, the volume fraction of the precipitate phase remained constant at approximately 50%, regardless of the sintering temperature. High-temperature compression tests indicated that both compacts exhibited higher compressive strength at 973 K compared to 1073 K. Microstructural characterization after deformation at 973 K showed that the FCC phase was refined via dynamic recrystallization induced by large strains, whereas the R phase was fragmented accompanied by microcrack initiation. Conversely, the grain sizes of the FCC and R phases remained almost unchanged after deformation at 1073 K, and the compacts exhibited lower flow stress resulting from superplastic deformation.

Near-eutectic high/medium entropy alloys containing brittle primary phases often suffer from limited ductility despite high strength. This study demonstrates that controlling the microstructure of brittle primary dendrites enables pronounced ductility enhancement in a near-eutectic NiCo15Cr15Al20 medium entropy alloy with B2 primary dendrites, without compromising ultimate tensile strength. Directional solidification combined with in-situ synchrotron X-ray imaging directly revealed how the misorientation angle between the thermal gradient and the primary dendrite growth direction governs the secondary/tertiary dendrite development. When the primary dendrites were aligned nearly 0˚ to the thermal gradient, secondary arm growth was suppressed, resulting in isolated dendrites embedded in eutectic regions that retard crack percolation. In contrast, specimens with ~30˚ misorientation developed connected dendritic networks promoting facile crack coalescence and premature fracture. The near 0˚ specimens exhibited a fivefold increase in tensile ductility (from 2.1% to 10.8%) while maintaining a high ultimate tensile strength of ~900 MPa compared to the near 30˚. Fracture analyses revealed that ductility is governed by crack coalescence pathways controlled by dendrite connectivity and the availability of ductile L12 phase ligaments. These results demonstrate that crack coalescence pathway control through dendrite alignment provides an effective strategy for simultaneously achieving excellent strength and ductility in near-eutectic alloys with brittle primary phases.

Inconel 718 is a Ni-based superalloy strengthened by γ″ and γ′ precipitates formed during a two-step aging treatment, and it has been widely utilized in aerospace and power generation industries owing to its excellent high-temperature mechanical properties.In this study, electrically assisted aging was employed to control the precipitation behavior of Inconel 718 and to achieve superior mechanical properties within a shortened processing time than conventional aging. Electrically assisted aging treatments were conducted, and the morphology, size, and distribution of precipitates were characterized.The results revealed that electrically assisted aging effectively accelerated precipitation compared with conventional aging, enabling the achievement of superior mechanical properties within a substantially reduced aging time. Furthermore, a unique co-precipitate structure, consisting of γ′ precipitates attached to the interface of γ″ precipitates, was observed under specific electrically assisted aging conditions, whereas such a structure was not observed after conventional aging. The accelerated precipitation kinetics and the formation of co-precipitates induced by electric current application suggest that athermal effects of electric current can influence atomic diffusion and precipitation processes near interfaces, thereby promoting a microstructural evolution distinct from that achieved through conventional aging. These results demonstrate that electrically assisted aging is an efficient aging process capable of effectively controlling the microstructure and mechanical properties of Inconel 718.

Spatially heterogeneous microstructures composed of coarse-grained (CG) and fine-grained (FG) regions have attracted considerable attention due to their ability to achieve an improved balance between strength and ductility. Among these, the harmonic structure (HS) design concept has demonstrated remarkable potential for enhancing mechanical performance. In this study, the deformation behavior of SUS316L with a refined harmonic structure (RHS) fabricated by mechanical milling and spark plasma sintering (MM/SPS) was investigated. A bimodal powder mixture consisting of SUS316L powders with average particle sizes of 26.3 and 6.4 µm at a weight ratio of 20:5 was mechanically milled at 200 rpm for 86.4 ks. Subsequently, the mechanically milled powder was consolidated by spark plasma sintering (SPS) at 1173 K under 100 MPa for 0.6 ks. EBSD analysis revealed an interconnected FG network (< 3 µm) surrounding CG core regions (> 3 µm), forming the RHS microstructure. Tensile test results demonstrated that the RHS material exhibited higher 0.2% proof strength and ultimate tensile strength (UTS) than a homogeneous counterpart with an average grain size of 4.3 µm, consistent with the strengthening effect generally observed in HS materials. Interestingly, however, the RHS material exhibited a distinct yield drop phenomenon. EBSD analysis after tensile deformation at ε= 0.1 showed a uniform Kernel Average Misorientation (KAM) distribution across both the FG network and CG regions, suggesting that the dislocation accumulation near the FG/CG interfaces promoted the abrupt release of pinned dislocations into the CG regions, resulting in the observed yield drop phenomenon.

In this talk, we will focus on the behavior of nanolayered nanocomposites made with extraordinarily “thick” interfaces under mechanical deformation. We will discuss efforts to characterize and design the morphology, size, and chemistry of the interface, especially in its third dimension (normal to the interface plane). Results from a model developed to simulate the dynamic interactions of individual dislocations and these heterostructured interfaces under applied stress will be presented. The talk will share our findings to date, which indicate that both the macroscopic and microscopic responses are sensitive to interface thickness and through-thickness chemical gradients. We will conclude with a discussion on the intriguing possibility to design heterostructured thick interfaces to attenuate shear concentrations and postpone instabilities without sacrificing strength.

Heterostructured and gradient materials (HGMs) offer superior mechanical and functional properties. This performance boost comes from "back stresses" created at the internal boundaries of the material's mixed structure. While techniques like surface mechanical grinding (SMGT), surface mechanical attrition (SMAT), and shot peening (RASP) can successfully create HGMs, we still lack a deep, comparative understanding of how each specific process affects the overall microstructure and material strength beyond just grain size. This presentation addresses this gap by: 1) Reviewing and comparing how different HGM processing methods influence microstructure-strength relationships, 2) Introducing new research on alternative fabrication methods, including SPEX-mill-based SMAT, high-pressure torsion, and skin pass rolling (using small-percentage rolling mill reductions) to create high-strength HGMs and 3) Analyzing the thermomechanical pathways unique to each processing approach.  Finally, the microstructural changes and property improvements across a variety of metals will be evaluated, exploring how different crystal structures and alloy complexities respond to these treatments.

Medium-entropy alloys (MEAs), a new member of structural materials family, have been actively studied in physical metallurgy research communities. In this work, the influences of internal parameters (i.e., microstructure and composition) and external ones (e.g., strain-rate and hydrogen environment) on multi-scale mechanical behavior of the heterostructured MEAs were explored through nanoindentation experiments. The results were discussed in terms of the underlying mechanism that can explain the role of the internal/external parameters in small-scale mechanical behavior.

Modern world increasingly demands materials with the combinations of properties historically considered mutually exclusive, e.g. strong and ductile, tough and stiff, while also having improved cost efficiency, sustainability and recyclability. Such a combination of demands can be addressed by heterostructured (HS) materials with hierarchical architecture formed by the spatial modulation of grain size heterogeneity while preserving the homogeneity of chemical composition. The optimisation of design and efficiency of HS requires adequate rheological models incorporating the specifics of their architecture. In this report, we propose the concepts of ‘thick yield surface’ and ‘internal stress cloud’ as modern tools better describing HS material rheology than the classical plasticity models. The concepts intrinsically reflect that (i) various grains in the representative material volume initiate the elastic-plastic transition at different stress levels leading to the ‘thickening’ of macroscopic yield surface, and (ii) the combination of local stress gradients with the thick yield surface creates a complex elastic-plastic interactions leading to unique rheology. In reference synchrotron-based experiments on harmonic-structured nickel, we found that (a)stress gradients build-up already during macroscopically elastic loading, (b)plastic yielding initiates in coarse grains while macroscopically the material appears elastic, and (c)the fine-grain network leads to higher macroscopic yield strength, the redistribution of stress gradients, and the formation of back- and forward- stresses. The new concepts enable simple description of the experimentally discovered complex phenomena and open more opportunities for HS architecture optimisation and property control.

Heterogeneous microstructures, including texture macrozones, mixed grain structure, and intragranular orientation gradients, govern strain partitioning, plastic localization, and failure in many structural metals. Full-field crystal plasticity (CP) modeling provides a physically based framework to connect microstructural heterogeneity with macroscopic mechanical response, processing history, and engineering performance. By combining mechanical testing, X-ray tomography, and CPFEM, we show that the transition between void driven damage and localization induced damage is controlled by the degree of deformation heterogeneity. A scalar heterogeneity parameter is introduced to rationalize damage mode transitions under the coupled effects of specimen size, thickness-to-grain-size ratio, and work hardening. For mixed-grain 316LN stainless steel, in-situ micro-tension experiments, grain-scale DIC, EBSD tracking, and full-field CP simulations are integrated to reveal the preferential deformation of millimeter-scale coarse grains and the compensating deformation band formation in surrounding fine grain regions. We further extend this framework to processing oriented applications. For near-α titanium alloys, multiscale characterization and CP simulations accounting for dislocation slip and grain boundary sliding clarify the mechanisms by which texture macrozones are weakened, fragmented, and ultimately eliminated during thermomechanical processing. These insights support a two-stage processing route based on lamellar spheroidization and superplastic deformation, providing a mechanistic pathway for macrozone control and grain refinement. For additively manufactured metals, a microstructure informed CP approach is developed by directly mapping experimentally measured orientation gradients and dislocation density fields into full-field simulations. This enables the prediction of intragranular shear band networks, stress triaxiality redistribution, and damage relevant localization patterns associated with strength-ductility synergy.

Intermetallic materials are bestowed with diverse ordered superlattice structures together with many unusual properties. In particular, the advent of chemically complex intermetallic alloys (CCIMAs), which are also called as the high-entropy intermetallic alloys (HEIMAs), has received considerable attention in recent years and offers a new paradigm to develop novel metallic materials for advanced structural applications. These newly emerged CCIMAs exhibit synergistic modulations of structural and chemical features, such as self-assembled long-range close-packed ordering, complex sublattice occupancy, and interfacial disordered nanoscale layer, potentially allowing for superb physical and mechanical properties that are unmatched in conventional metallic materials. In this talk, we will review the historical developments and recent advances in ordered intermetallic materials from the simple binary to chemically complex alloy systems. We are focused on the unique heterogeneous structures, including multicomponent superlattice microstructures, nanoscale grain-boundary segregation, and disordering, as well as the various extraordinary mechanical properties of these newly developed CCIMAs. Finally, perspectives on the future research orientation, challenges, and opportunities of this new frontier are provided. This conceptual design of CCIMAs may lead to families of high-temperature structural alloys, which will be of great interest for a broad range of aerospace, automotive, nuclear power, chemical engineering, and other applications.

Multi-material additive manufacturing opens a new avenue for materials design and synthesis, but also increases the complexity in the process-structure-property relationships. To this end, we have developed and seamlessly integrated a series of high-fidelity multi-physics models for multi-material additive manufacturing. Specifically, multiphase flow models using the coupled computational fluid dynamics (CFD) and discrete element method (DEM) simulate the motions of unmelted powder particles in the melting procedure of nano- and micro-particle reinforced composites. For the cases where different powders are melted for in-situ alloying, the model incorporates the major physical factors, e.g., the composition evolution due to evaporation and convection, the varying thermo-physical material properties dependent on the local chemical compositions, and the heat release/absorption due to alloying/chemical reactions. The microstructure evolutions at both the grain- and dendrite- scales are modelled using the phase field and cellular automaton methods. The mechanical properties and thermal stresses are simulated using the crystal plasticity finite element (FE) model, which incorporates the realistic geometry (rough surfaces and voids), temperature profiles and microstructures including the interactions between reinforcing particles and dislocations. These models have proven to be useful in revealing the physical mechanisms and guiding manufacturing process optimization, which have been validated against experiments.

Additive manufacturing (AM) is transforming materials design by enabling architected heterostructures whose properties can transcend conventional rule-of-mixtures predictions through synergistic interactions across multiple length scales. By providing unprecedented control over geometry, interfaces, defects, and microstructural gradients, AM offers the possibility of achieving property combinations that are difficult to realize through conventional manufacturing routes. This presentation demonstrates the potential of severe plastic deformation (SPD), when integrated with AM, as a powerful microstructural engineering tool for tailoring such heterostructures.Using laser powder bed fusion (LPBF) AlSi12, AlSi10Mg, and 316L stainless steel as representative systems, this work highlights how post-AM SPD routes, including equal-channel angular extrusion/pressing, high-pressure torsion, and friction stir processing, transform as-built, defect-rich microstructures into refined heterostructures with ultrafine grains, well-distributed precipitates, and improved densification leading to better structural integrity at multiple scales. These microstructural transitions generate concurrent gains in strength, toughness, fatigue resistance, and damping response, while also providing unique mechanisms for internal stress accommodation and improved strength-ductility synergy.Across the investigated alloy systems and processing routes, these examples demonstrate that linking AM-enabled architectures with optimized SPD routes offers a pathway for the design of high-performance heterostructured materials. By exploiting interactions between heterogeneous microstructural regions, defects, and interfaces, this integrated manufacturing strategy overcomes intrinsic material limitations and presents new opportunities for engineering components with simultaneously enhanced structural and functional performance.

Severe plastic deformation methods are efficient in producing heterostructured and ultrafine-grained materials with advanced properties. While the main focus on such materials is on their mechanical properties, they have high potential for functional properties. It was shown that such materials can break the strength-ductility trade-off [1] and provide high potential for energy applications, including hydrogen storage [2], hydrogen embrittlement resistance [3], and photocatalytic hydrogen production [4]. The current author and his colleagues mainly use high-pressure torsion and surface severe plastic deformation methods to achieve such microstructures. This talk reviews some recent advances in developing heterostructured materials for superfunctional applications with a focus on functional property – microstructure correlations.[1] A. Mohammadi, X. Sauvage, F. Cuvilly, K. Edalati, J. Mater. Sci. Technol. 203 (2024) 269-281.[2] K. Edalati, M. Novelli, S. Itano, H.W. Li, E. Akiba, Z. Horita, T. Grosdidier, J. Alloys Compd. 737 (2027) 337-346.[3] A. Mohammadi, M. Novelli, M. Arita, J.W. Bae, H.S. Kim, T. Grosdidier, K. Edalati, Corros. Sci. 200 (2022) 110253.[4] J. Hidalgo-Jiménez, T. Akbay, M. Watanabe, K. Saito, Q. Guo, T. Ishihara, K. Edalati, J. Energy Chem..111 (2025) 954-968.

With the recent production of electric vehicles, the importance of thermal management systems has become increasingly apparent. Aluminum clad sheets for brazing, with their excellent thermal conductivity and high specific strength, are widely used to reduce the weight of automotive heat exchangers and improve energy efficiency. To reduce the weight of heat exchanger components, it is essential to increase the strength of the aluminum sheet used, thereby reducing the thickness of the fins and tubes, while minimizing the deterioration of mechanical properties during brazing. In this study, 3003 aluminum alloy strips and 4343 alloy strips, which serve as braze metals, were manufactured using Twin Roll Casting. These strips were rolled and laminated in three layers with a thickness ratio of 1:8:1 to form a 4343:3003:4343. These plates were then fabricated into 4343/3003/4343 clad sheet using a rolling bonding process. The clad sheets were rolled to thicknesses of 200, 150, and 100 µm and subjected to intermediate heat treatments at various temperatures. Finally, the clad sheets were further rolled to a thickness of 70 µm, producing aluminum clad thin sheets suitable for use as heat exchanger fins. The microstructure and tensile properties of the clad fins were evaluated, and the effects of microstructural changes on tensile properties were investigated. Microstructural changes in these fin materials were observed after heat treatment at the brazing temperature. The effect of the initial microstructure of fins on erosion resistance during brazing was evaluated, and a microstructural control method for improving erosion resistance was proposed. 

EnterThermal conductivity (TC) and expansivity (TE) of heat sinks are crucial properties for microelectronic packaging. High TC is required to remove the heat generated on the component parts, but a low coefficient of TE is essential to reduce the thermal stress and improve the dimensional stability of the electronic packaging. In this study, we present a new type of aluminum nitride (AlN) reinforced aluminum matrix composites with hypereutectic Al-Si alloys. The novel composites are produced by in situ reaction between liquid aluminum and nitrogen gas through arc plasma-induced accelerated volume nitridation. We demonstrate that a volume fraction of AlN reinforcements can be increased up to around 30% depending on the nitridation reaction time and matrix composition. Our results propose that the Al/AlN composites could exhibit an attractive combination of high TC and low TE, which is highly desirable for heat sink materials.

The fatigue behavior of Ti-6Al-4V alloys is strongly influenced by their microstructural design, particularly in the case of heterogeneous architectures such as harmonic structures. These materials, consisting of coarse-grained cores embedded in a continuous fine-grained shell, offer an attractive combination of strength and ductility. However, their reliability under cyclic loading and the role of specimen size remain insufficiently understood. In this study, the fatigue properties of a Ti-6Al-4V alloy processed via powder metallurgy and exhibiting a harmonic structure are investigated under four-point bending loading conditions. Two specimen configurations, namely miniature and standard sizes, are considered to evaluate the influence of specimen size on fatigue strength. The results reveal a pronounced size effect in the harmonic structured material, with a significant reduction in fatigue endurance observed for larger specimens, whereas a homogeneous coarse-grained counterpart shows negligible size dependence. Fractographic analyses indicate that fatigue crack initiation predominantly occurs within coarse-grained core regions, regardless of specimen size. However, additional initiation mechanisms, including defect- and inclusion-induced failures, are observed in larger specimens, contributing to the reduced fatigue performance. Furthermore, electron backscatter diffraction analyses highlight differences in local deformation behavior, suggesting that the interaction between core and shell regions evolves with specimen size. The combined effects of microstructural heterogeneity and stressed volume must be considered to ensure reliable structural applications.

Mechanical components often fail by fatigue initiated at notches where stress concentration occurs, making mitigation of the notch effect a critical issue for structural reliability and materials design. In this study, harmonic structural design, originally developed to achieve a superior balance of high strength and high ductility in metallic materials, is applied to the elimination of the notch effect in fatigue. Axial fatigue tests were conducted on notched specimens with a harmonic structure fabricated by mechanical milling and spark plasma sintering, and their fatigue behavior was systematically evaluated. The results demonstrate that the presence of a notch did not reduce the fatigue limit of harmonic-structured austenitic stainless steels, indicating an effective disappearance of the notch effect. In contrast, the fatigue limit of homogeneous counterparts was significantly decreased by the notch. Fractographic observations and surface analyses revealed that fatigue cracks in the notched specimens preferentially initiated within the fine-grained regions, which exhibit higher strength, whereas fatigue cracks initiated at the coarse-grained regions in the smooth specimens. This contrasting fatigue crack initiation behavior is attributed to stress partitioning in the fine-grained structure in the harmonic structure by the plastic deformation at notch root.

Pure magnesium exhibits poor room-temperature ductility and toughness. Gradient structure, a typical class in heterostructure materials, normally enhances the mechanical strength of metals while not compromising ductility. In this study, a gradient structure characterized by an ultrafine-grained surface layer and a deformed core was fabricated in pure magnesium using ultrasonic surface rolling. Results show that this gradient structure resulted in a slight increase in yield strength but significantly enhanced total elongation. Further tensile testing revealed that grain boundary sliding occurred in the ultrafine-grained surface layer during tensile deformation, contributing to excellent ductility. The softened surface layer, along with the hardened deformed core, realized significant toughness enhancement in pure magnesium.

Heterogeneous grain structured high-entropy alloys (HEAs) exhibit excellent strength-ductility synergy due to the peculiar grain structure topology. However, the understandings of tensile and cyclic response as well as deformation mechanism are still inadequate. Therefore, the tensile behavior, low-cycle fatigue behavior and fatigue crack growth behavior of CoCrFeMnNi HEAs with a three-dimensional core–shell grain structure were investigated. The effects of core–shell network structure on plasitic deformation, cyclic response, fatigue life as well as fatigue crack growth rate are revealed. The dislocations activity dominantly appears in the soft core regions prior to the hard shell region. The LCF resistance remains when the strain amplitude is below 0.5%. Moreover, the network core–shell structure generates the crack deflection, enhancing roughness-induced crack closure.Enter description here.

Heterostructured SAF2507 duplex stainless steel (HDSS) was successfully fabricated via 90% cold rolling followed by short-time normalization at 1273 K for 1 min. The distinct heterogeneous microstructure stems from higher geometrically necessary dislocations (GNDs) density and a larger hardness difference between ferrite and austenite phases. Mechanical tests showed the heterostructured sample achieved a yield strength of 715 MPa and ultimate tensile strength of 939 MPa, remarkably higher than the coarse-grained (CG) sample (541 MPa and 795 MPa), while retaining a uniform elongation of 24.8%, close to the CG sample’s 25.2%. HDSS generates higher geometrically necessary dislocation density during plastic deformation, and the strengthening effect of the hetero-deformation-induced (HDI) stress plays an important role in enhancing the yield strength of the material. Moreover, the HDI stress strain hardening and twinning-induced plasticity (TWIP) effect (35% twin boundaries generated during tension) synergistically maintained excellent ductility. Electrochemical corrosion tests confirm that the constructed heterogeneous structure effectively optimizes surface passivation behavior, remarkably improves pitting resistance and forms denser and more stable passive films to slow down corrosion infiltration. The coordinated improvement of mechanical properties and corrosion resistance endows HDSS with broader application prospects in harsh corrosive service environments, and provides a reliable technical path for high-performance duplex stainless steel design and performance regulation.

Achieving high yield strength while precisely controlling deformation behavior remains a fundamental challenge in metallic structural materials. Although multiscale heterostructures are widely used for strengthening, the deliberate modulation of deformation behavior has proven elusive. Here, we overcome this limitation by introducing a tailored heterostructure combination into a transformation-induced plasticity (TRIP)-assisted Co74Ni20V6 medium-entropy alloy through thermomechanical processing. The resulting partially recrystallized microstructure integrates fine heterogeneous grains, large-sized stacking faults in unrecrystallized regions, chemical medium-range order (CMRO), and interconnected defect networks. This architecture activates pronounced hetero-deformation induced strengthening, ensuring high yield strength. Notably, the localized atomic distribution and atomic-scale strain fluctuations arising from dispersed CMRO, coupled with interactions between CMRO and other heterostructures, effectively decelerate martensitic transformation kinetics, thereby enhancing uniform deformability and sustained work hardening throughout deformation. Compared with a homogeneous coarse-grained counterpart, the tailored alloy achieves a 274% increase in yield strength, an 84% increase in ultimate tensile strength, and a 93% increase in fracture elongation. This work establishes a transformative paradigm for optimizing the strength-ductility synergy in TRIP-assisted alloys through the strategic design of tailored heterostructures, offering a compelling pathway for next-generation structural materials.

The present study systematically investigates the microstructural evolution (precipitation, texture, grain structures), & their correlations with the mechanical properties of thermo-mechanically processed (TMPed) 7075 Al alloy subjected to cold rolling (CR) followed by artificial ageing (T6) after solution quenching (SQ). The SQ condition remains precipitate-free, whereas peak ageing (T6) promoted the formation of η′, η (hP12 Laves phase: MgZn₂), Al₂Cu, and Al₂CuMg precipitates. TMP significantly altered the precipitation behavior, with η′ predominantly observed in TMP-1 and TMP-2, while the equilibrium η phase became dominant in TMP-3. In the T6 condition, pronounced recrystallization textures Goss {011} and P {011} were developed. In contrast, the TMPed alloys exhibited strong deformation textures of S {123} and Rt-cube in TMP-1,  Cu {112} in TMP-2 and TMP-3, along with Goss and P textures. Progressive deformation resulted in randomization of the texture (24R to 16R). Enhanced strengthening was achieved via the heterostructure deformation behavior, e.g., dislocation–precipitate interactions, bimodal grain size, and texture, leading to yield strengths of 485 ± 7 MPa (TMP-1), 508 ± 3 MPa (TMP-2), and 520 ± 5 MPa (TMP-3), compared with the 302 MPa and 353 MPa for the SQ and T6 conditions. The presence of a relatively soft phase of Al₂Cu and η′, increased low-Σ3 CSL boundaries, and higher fractions of high-angle grain boundaries contribute to improved ductility up to 23% in the TMPed alloys. Residual stress increases with deformation, reaching −162 ± 8 MPa in TMP-3. These heterogeneities also change the deformation behavior from the Swift to Ludwigson with TMP.

Some heterogeneous structures have been proved benefitial for simultaneous enhancement of strength and ductility of metallic materials. Heterogeneous structures in metallic materials can be introduced by various methods, including surface plastic deformation, laser shock peening of surface, and chemical/physical deposition. Recently, there has been growing interest in using additive manufacturing (AM) techniques to produce heterogeneous metallic structures. AM of metallic materials involves cyclic rapid thermal loadings that significantly impact the microstructure and consequently the mechanical properties of the materials. During the AM processes, different layers experience different thermal histories, leading to microstructure variation along the build direction. Further, the layer-by-layer deposition during the AM processes makes it possible to precisely manipulate local composition. In this presentation, I will examine the impact of structural heterogeneity on the mechanical properties of AM materials and explore the potential for leveraging AM processing to create hierarchical heterogeneous structures for outstanding mechanical performance.

Additive manufacturing (AM) offers an unprecedented design freedom to engineer unique heterostructured microstructures that overcome the traditional strength-ductility trade-off through hetero-deformation induced (HDI) hardening. This study provides a comprehensive overview of microstructure tailorship and mechanical property synergy across diverse metallic systems fabricated via laser powder bed Fusion (LPBF), material extrusion additive manufacturing (MEAM), and wire arc additive manufacturing (WAAM) etc. First, we investigate high-entropy alloys (HEAs), including the classic Cantor alloy and medium-entropy NiCoCr alloys etc., processed by LPBF. The rapid solidification inherent in LPBF triggers hierarchical heterostructures consisting of cellular networks, dislocation sub-structures, and local chemical fluctuations, leading to prominent twin-induced plasticity (TWIP) and HDI effects. Second, the structural evolution of challenging materials—pure copper (Cu) and 17-4PH stainless steel etc.—fabricated via MEAM is evaluated. By optimizing debinding and sintering profiles, controlled multi-modal grain distributions and heterogeneous precipitate layouts are successfully achieved, enabling high electrical/thermal performance alongside robust strength. Finally, large-scale structural Al and Ti alloys synthesized via Wire-based M are presented. Due to the repeated thermal cycling in directed energy deposition, these alloys naturally develop macroscopic and microscopic heterostructures, such as alternating columnar-to-equiaxed grain zones (CET) and graded secondary phase distributions. The microstructural heterogeneity, mechanical responses, and fundamental deformation mechanisms of these five distinct alloy systems are compared systematically. The findings demonstrate that strategic utilization of AM-induced thermal histories serves as a powerful toolkit for designing next-generation, high-performance heterostructured materials.   Keywords: Heterostructured Materials, Additive Manufacturing (LPBF/MEAM/WAAM), High-Entropy Alloys, Conventional engineering alloys, Microstructure, Mechanical property.

Designing structural materials with high strength and good plasticity has always been a hot topic and challenge in scientific research and industrial applications. To achieve this goal, researchers have proposed the creation of multiscale heterogeneous structures to manufacture structural materials with excellent overall performance. However, designing multiscale intragranular heterogeneous microstructures, especially in titanium alloys, still faces many difficulties. Additionally, there are challenges in scaling up small-scale laboratory techniques for large-scale industrial applications.In this talk, We will introduce a novel approach that combines thermodynamic databases, phase-field simulations, and additive manufacturing for heterogeneous material design and mechanical performance enhancement. Through phase-field simulations, we demonstrate the design of precursor phase-separated organizations and two-step aging processes for designing materials with multiscale layered heterogeneous dual-phase structures. Furthermore, we utilize additive manufacturing techniques to achieve a novel metastable heterogeneous dual-phase organization at the micron scale. The deformation mechanism in the complex materials will also be investigated. This new microscale concentration-modulated organization exhibits excellent mechanical properties. This additive manufacturing-based approach creates a new pathway for designing concentration-modulated heterogeneous alloys and can be applied to the design and development of various structural and functional materials.

Multi-material additive manufacturing (AM) enables dissimilar metals to be spatially integrated into single components, offering design freedom for lightweight structural applications. Such joints are intrinsically heterostructured, combining chemically and mechanically dissimilar domains across nanometer-to-micrometer length scales. Joining metallurgically incompatible systems such as steel and aluminum, however, remains a long-standing challenge: brittle Fe–Al intermetallic compounds (IMCs), notably Al5Fe2 and Al13Fe4, readily form at the interface and severely degrade bonding strength, and conventional welding cannot suppress them because of local equilibrium at the liquid/solid front. This talk shows how powder bed fusion (PBF) offers a new route to tame these brittle phases by exploiting its rapid, far-from-equilibrium solidification to govern interfacial phase selection. In laser beam PBF (L-PBF) of carbon steel/Al3Si1Mn, increasing the scanning speed raised the solidification rate toward absolute stability (~1 m/s), invoking a solute-trapping effect that suppressed coarse brittle IMCs and promoted ductile α-Al; the bonding strength rose from 27 to 103 MPa. Extending this to electron beam PBF (EB-PBF) of 304 stainless steel/AlSi10Mg, powder-bed preheating and lower effective line energy yielded a thinner, discontinuous IMC layer and superior bonding relative to L-PBF, confirming an inverse IMC-thickness–strength relationship. Across both systems, machine learning accelerated process-window identification. These results identify energy input and melt-pool dynamics as the key factors governing brittle interfacial reactions, providing practical guidelines for designing robust heterointerfaces in dissimilar-metal AM.

Multi-Material Laser Powder Bed Fusion (MM-LPBF) Additive Manufacturing is showing promising capabilities for all-in-one fabrication of multiple materials in a single part. Because of the layer-by-layer nature of LPBF, any complex 3D multi-material structure can be simplified to the interfacial bonding of two dissimilar materials, both horizontally and vertically. This talk presents our latest work on interfacial bonding between dissimilar metals in MM-LPBF, including both horizontal and vertical interfaces. To thoroughly understand interfacial bonding behaviours and underlying mechanisms, material redistribution at the interface under liquid convection will be analysed. The microstructural development across the interface will be compared. Eventually, the mechanical performance of bonding strength, microhardness, and micro-modulus across the interface will be revealed, connecting the micro-world to the macro-world. The model material combinations Steel/Nickel/Copper, Steel/Nickel, Nickel 1/Nickel 2, and Nickel/Copper are selected to elucidate the fundamental theories and mechanisms underlying interfacial bonding. In particular, we will share a micronozzle-controlled powder bed layout strategy, inspired by Continuously Variable Transmission (CVT) mechanics, to fabricate heterogeneous gradient interfaces by docking thickness gradients of two dissimilar powder layers. This approach, for the first time worldwide, enables flexible adjustment of composition without pre-mixing powders between two different metals, even within each ~100 μm-thick powder layer, while also allowing programmable vertical spatial arrangement of the two materials within a powder layer. The data and printing experience from these studies would be welcomed and transferable to other metal combinations in MM-LPBF.

Digital light processing offers a promising approach for fabricating Ti-6Al-4V components with high resolution and complex geometries. However, metal photopolymerization remains challenging because highly loaded metal slurries require simultaneous control of curing behavior, suspension stability, layer formation, debinding, and impurity evolution during sintering. In this study, we establish a digital light processing route for Ti-6Al-4V through coordinated control of powder characteristics, resin formulation, layer formation, and debinding behavior. Powder classification improved the curing behavior of the Ti-6Al-4V slurry, while the resin formulation was optimized to provide stable printing and effective debinding. A solvent-debindable polyethylene glycol component was introduced to create interconnected pathways in the green body after extraction, which facilitated gas release during thermal debinding and reduced the required thermal debinding time. Using the optimized process, Ti-6Al-4V components were successfully fabricated with high density, submicrometer as-sintered surface roughness, and tensile strength exceeding 1.1 GPa. Extract-based in vitro testing also indicated no detectable cytotoxicity under the present conditions. These results suggest that reliable Ti-6Al-4V digital light processing requires a coordinated control of powder, resin, layer formation, and debinding behavior. The proposed approach provides a practical route toward high-precision titanium additive manufacturing for biomedical applications

The manufacturing quality of 46XX cylindrical battery cans is strongly governed by process-induced defects and dimensional variations generated during deep drawing, trimming, and riveting. This study investigates several possibilities of quality issues in Ni-plated steel 46XX can manufacturing and proposes process control strategies for improving the quality and reliability of 46XX high-capacity cylindrical battery cans. In the deep drawing process, thickness thinning, fracture risk, wrinkling, earing-related defects, and dimensional deviation are analyzed to optimize the multi-stage forming sequence. In the trimming process, cut-edge defects such as burr, die roll, tear-off, and height deviation are controlled through tool and clearance optimization. In the riveting process, local deformation of the can–rivet–gasket system and potential failure risks are evaluated to ensure robust assembly quality. The results provide an integrated process optimization framework for achieving high dimensional accuracy, stable manufacturability, and reliable structural performance of 46XX cylindrical battery cans.

Heterostructuring is an emerging method for achieving an excellent combination of strength and ductility; however, its usage is often limited in the industry because of poor formability. The high mechanical incompatibility between domains in heterostructured materials facilitates crack initiation and propagation during forming. To broaden the industrial applicability of heterostructured materials, it is necessary to balance their tensile properties and formability. Herein, we propose a new strategy for designing heterostructures that are optimized for forming. Cold-rolled CoCrFeMnNi high-entropy alloy sheets were laser-treated on both sides to fabricate an inverse-gradient structure (soft outer and hard inner regions) for superior strength-ductility synergy. The resultant heterostructure induces excellent strength and ductility combination through significant HDI hardening. Furthermore, the inverse-gradient samples exhibited excellent bendability because the outer coarse-grained region prevented the generation of external cracks, and the decrease in the strength difference between neighboring domains reduced the damage evolution in severe deformation of forming.

This study investigates a cobalt-free Al-V-Cr-Fe-Ni eutectic medium-entropy alloy (EMEA) synthesized via additive manufacturing for nuclear applications, eliminating cobalt to prevent long-term radioactive activation. Elemental analysis shows distinct chemical partitioning across the phases, while transmission electron microscopy (TEM) confirms a complex microstructure consisting of B2, BCC, and FCC phases with defined crystallographic orientation relationships. To optimize the mechanical performance and environmental resistance of the alloy, post-processing heat treatments and radiation tolerance tests are employed to tailor the microstructural evolution and phase stability. This work establishes a baseline for developing high-performance, radiation-tolerant structural materials.

Titanium alloys have attracted considerable attention for aerospace and transportation applications due to their high specific strength and excellent corrosion resistance. However, since titanium alloys exhibit low elastic modulus and poor high-temperature strength compared to conventional alloys, titanium matrix composites (TMCs) reinforced with high-strength particles or whiskers have emerged as a promising solution. Due to the high oxygen affinity of titanium, the fabrication methods of TMCs have been largely restricted to solid-state processing techniques such as powder metallurgy and spark plasma sintering. These methods require additional steps to achieve uniform dispersion of reinforcement prior to sintering, limiting the maximum reinforcement typically up to 20 vol.%. Moreover, they exhibit defects such as high porosity, agglomeration, and weak interfacial bonding due to poor wettability between the metal-ceramic leading to deterioration of mechanical properties. In this study, we fabricated Ti(W)-TiC composites by reacting WC particles with pure titanium melts through arc-plasma melting. This process facilitated a spontaneous reaction between the melt and WC particles, resulting in the in-situ formation and uniform dispersion of thermodynamically stable TiC within the matrix, reaching 70 vol.%. We analyzed microstructural evolution with increasing WC content and evaluated the effects of solid-solution strengthening of W and the increased TiC fraction on the mechanical properties through compression tests at various temperatures.

Enter description hereCold-sprayed Ni and Ti coatings were deposited on sensitized SS304 substrates, representing heat-affected regions of spent nuclear fuel dry storage canisters, to enhance pitting corrosion resistance for CISCC (Chloride-Induced Stress Corrosion Cracking) mitigation and examine microstructural evolution during deposition. FeCl₃ immersion and anodic polarization tests were performed to examine the corrosion behavior, while XRD, EBSD, and TEM were employed for microstructural characterization. Microhardness testing was also conducted to assess the mechanical response associated with powder deformation during cold spray deposition. Both coatings provided improved corrosion resistance compared with bare SS304 and exhibited material-dependent dynamic recrystallization behavior. In the FeCl₃ immersion test, the Ni coating underwent relatively uniform corrosion with localized attack along powder boundaries, whereas the Ti coating remained largely unaffected. Anodic polarization results showed clear passivation in the Ti coating, while the Ni coating exhibited little to no passivation behavior. Galvanic coupling tests conducted on artificially defected coated samples showed that degradation of the Ti-coated specimens was minimal and confined to the exposed substrate region, whereas in both the coating layer and the underlying substrate. The stable passive film formed on the Ti-coated sample was supported by the passive region observed during anodic polarization and the oxide film confirmed by TEM after the immersion test. These results indicate that cold-sprayed Ti coating may be a promising corrosion-resistant barrier for dry storage canister applications..

Amid the global push toward carbon neutrality, nuclear power has re-emerged as a viable low-carbon energy source. Reactor pressure vessel (RPV)-grade low alloy steels are critical structural materials for ensuring the structural integrity and safety of small modular reactors (SMRs). In the present study, we systematically investigated the cleanliness and oxidation behavior of electrode inert gas atomization (EIGA)-produced low-alloy steel powders with different particle-size ranges. The total oxygen (T.O.) content decreases with increasing particle size, primarily governed by the reduced specific surface area of coarser powders. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) show that the powder surface is covered by a continuous oxide layer, mainly composed of Fe2O3 and MnO, with a thickness of approximately 6-8 nm. In addition to surface oxidation, oxide inclusions inherited from the electrode were extracted and characterized, revealing the three-dimensional morphology in the powder state. During HIP consolidation, the surface-derived Mn-Si-O oxides undergo Ostwald ripening or reduction by oxide layer leading to particle coarsening. Charpy V-notch tests demonstrate an inverse correlation between absorbed energy and T.O. content. Large inherited oxide inclusions promote the formation of coarse dimples, whereas thicker surface oxide layers weaken interparticle bonding, facilitate particle-particle boundary formation, and provide preferential paths for crack propagation. This work provides a mechanistic link between powder oxidation, inherited inclusions, particle-particle boundary formation and impact toughness degradation in HIP-consolidated RPV-grade steels.Keywords: EIGA, Surface oxidation, Non-metallic inclusions, PM-HIP, Impact toughness.

Powder metallurgy combined with hot isostatic pressing (PM-HIP) is an emerging manufacturing process for nuclear reactor pressure vessels. Optimizing HIP parameters requires a deep understanding of the microstructural mechanisms governing fracture toughness. In this study, atomized SA508 powder was consolidated at three different HIP temperatures. To isolate temperature effects, the cooling rate was strictly controlled at 10.5±0.3 ℃/min, and a subsequent normalizing heat treatment was applied to equalize the prior austenite grain size (PAGS).   Despite the identical PAGS and cooling histories, Charpy V-notch tests revealed that the impact toughness deteriorated significantly with increasing HIP temperature, dropping from ~150 J at the lowest temperature to ~118 J at the highest temperature. The area fraction of cementite consistently observed under all evaluated conditions. However, the standard deviation of cementite area fraction increased notably at higher temperatures, indicating coarser phase and severe microstructural heterogeneity.   Elevated HIP temperatures intensified localized cementite precipitation and clustering. These heterogeneous, carbide-dense regions acted as stress concentrators, facilitating early cleavage crack initiation and inducing premature brittle fracture. These findings confirm that microstructural homogeneity—specifically uniform cementite dispersion—governs the impact toughness of SA508 steel more profoundly than the absolute carbide area fraction or PAGS. Consequently, employing relatively lower HIP temperatures within the processing window is critical to suppress localized cementite clustering and secure the superior fracture toughness required for nuclear applications.

For high-density high-bandwidth memory stacking, low-temperature Cu–Cu diffusion bonding is required to reduce the bonding thickness between Cu interconnects while maintaining sufficient strength and reliability. This study proposes a Hybrid Copper Bonding -based bonding strategy using micro-cone arrayed Cu surfaces. The micro-cone features are designed to locally penetrate the opposing Cu interface, inducing mechanical interlocking and promoting atomic diffusion during subsequent heat treatment. Firstly, (111)-oriented Cu films were deposited by rotating disk electrodeposition, followed by chemical-mechanical polishing to prepare flat bonding surfaces. Micro-cone-arrayed Cu layers were then fabricated by controlling the additive composition and electrodeposition conditions. Before bonding, hydrazine treatment was performed to suppress native Cu oxide formation and activate the Cu surface. Bonding was conducted in air using a flip-chip bonder, with one side having a micro-cone array and the other side having a polished (111)-oriented Cu surface, followed by thermal annealing.The micro-cone arrayed Cu layer formed nano-twin structures, which are expected to enhance Cu diffusion and interfacial bonding. The micro-cone-bonded specimens showed higher bonding strength than planar (111)-Cu bonded specimens. SEM analysis also confirmed that interfacial voids were significantly reduced after annealing, indicating effective diffusion bonding. Therefore, this approach can enable thin, reliable Cu interconnects for future HBM stacking while relaxing process constraints associated with conventional high temperature bonding and supporting higher stack integration with improved interfacial integrity and overall thermal stability.

Efficient and safe hydrogen storage materials are essential for advancing hydrogen energy systems and supporting global decarbonization. Solid-state hydrogen storage using metal hydrides offers high volumetric hydrogen density, operational safety, and reversible hydrogen absorption–desorption characteristics. In this study, a heterostructured TiZrCrMnFeNi high-entropy alloy (HEA) is proposed as a novel material for hydrogen storage applications. The heterostructured architecture, consisting of microstructural domains with varying grain sizes and phase distributions, is designed to enhance hydrogen diffusion kinetics, increase active adsorption sites, and improve structural stability during repeated hydrogenation–dehydrogenation cycles. The interaction between heterogeneous interfaces and lattice distortions promotes faster hydrogen transport and better strain accommodation, thereby reducing performance degradation during cycling. Furthermore, the heterostructured design is expected to improve heat transfer during hydrogen absorption and desorption. The proposed alloy shows significant potential for application in metal hydride reactors, hydrogen compressors, heat pumps, and thermal energy storage systems, offering a promising pathway toward next-generation hydrogen storage technologies.

While it is well-know how the mechanical properties of polycrystalline materials depend on texture and grain size, it is also strongly influenced by the properties of grain boundaries. Grain boundary structure affects whether dislocations from within the matrix will be blocked (giving rise to Hall-Petch strengthening), absorbed, transmitted into the adjoining grain, grain boundary sliding or a combination of these. Such effects control the back-stress created within grains; a key feature of the design philosophy of heterostructured materials for optimizing strength and ductility. We propose a rigorous interface boundary condition built upon the defect structure of grain boundaries and Burgers vector reaction kinetics. We then demonstrate how this effects dislocation plasticity within the grains. We then show how this provides a predictive framework for dislocation dynamics – including dislocation transmission, blocking, absorption and grain boundary sliding as well as their influence on plasticity in the adjoining grains.

Understanding the atomistic mechanisms of inelastic deformation in metallic glasses (MGs) remains challenging due to their amorphous structure, in which local carriers of plasticity cannot be easily defined. Using molecular dynamics (MD) simulations, we analyzed the onset of inelastic deformation in CuZr/NiNb MGs, specifically the temperature dependence of the elastic limit, in terms of localized shear transformation (ST) events. We find that although the ST events initiate at lower strain with increasing temperature, the elastic limit increases with temperature in certain temperature ranges. We explain this anomalous behavior through the framework of an energy-strain landscape, revealing that the anomalous temperature dependence of the elastic limit is caused by the transition of ST events from irreversible to reversible with increasing temperature. To achieve MGs with unique atomic packing structures for more reversible STs, we fabricate monolithic Ni-Nb metallic glass films, experimentally demonstrated 6.6% elastic strain limit by in-situ transmission electron microscopy observations. The origin of high elastic strain limit may link with high free volume in the film, causing the rearrangement of loosely bonded atomic clusters (or atoms) upon elastic deformation. This high elastic limit of metallic glass films will shed light on new application fields for metallic glasses, and also trigger more studies for deformation mechanism of amorphous materials in general.

One of the defining features of fusion-based additive manufacturing (AM) processes is the localised melting of the metal by a high-energy source, which sequentially fuses the material together to form a 3-D object.By varying the AM parameters point by point throughout the build (e.g., the power of the energy source or the velocity it moves at), it is possible to change the local solidification conditions to manipulate the resulting material’s microstructure.This strategy opens the path to producing 3-D metal components that integrate controlled distributions of multiple, dissimilar microstructures. When designed with a purpose, these heterogeneous microstructures unlock new properties and functionalities in metal components.In this presentation, I will give a few examples of microstructure control and design using AM, focusing on different types of steels. I will review their unique behaviour and discuss the challenges and opportunities that this new materials design paradigm has to offer.

Under the growing demands of higher strength on structural materials, microstructures of advanced high-strength metallic alloys have become more and more complicated. The microstructures are in many cases composed of multi-phases having different mechanical properties. In the present study, we tackled to quantitatively evaluate stress/strain partitioning between hard phase and soft phase in multi-phased alloys using state-of-the-art experimental techniques. The micro-DIC (digital image correlation) analysis and in-situ neutron/synchrotron X-ray diffraction during tensile deformation were applied to the dual-phase steels composed of soft ferrite and hard martensite phases for analysing strain and stress partitioning, respectively, between the phases during deformation. From the average strain and stress amount in each of two phases obtained from the DIC and diffraction methods, we could reconstruct the stress-strain curves of ferrite and martensite separately for the first time. It was interestingly found that the stress-strain behaviour of two phases, especially that of the hard phase (martensite), greatly changed with increasing the density of inter-phase boundaries between two phases, leading to excellent strength-ductility synergy of the whole material having the particular morphology of the dual-phase microstructures. The result indicates that the deformation constraint through inter-phase boundaries plays a critical role to maximize deformation ability of hard phase(s) in alloys with multi-phase microstructures Reference:  Acta Materialia 292 (2025) 121061

Chemical heterogeneity across multiple length scales is a characteristic feature of additively manufactured high-strength steels. This heterogeneity can profoundly affect phase transformation behavior, microstructural evolution, and mechanical performance, presenting both challenges and opportunities for alloy design. This talk will focus on representative additively manufactured high-strength steels, including maraging steels and hot-work tool steels, to elucidate the formation mechanisms of chemical heterogeneity during additive manufacturing. Particular emphasis will be placed on strategies for harnessing chemical heterogeneity to tailor microstructures and improve strength–ductility synergy. The presentation aims to highlight chemical heterogeneity as an active microstructural design parameter for developing next-generation additively manufactured high-performance steels.

Laser powder bed fusion (LPBF) is a key technology for fabricating complex, high-precision components for aerospace and biomedical applications, yet its sustainability depends strongly on maximizing the reusability of residual feedstock powder. Since repeated thermal exposure during reuse affects build microstructure and mechanical performance is essential. Here, we systematically investigate the microstructure and 77 K tensile properties of LPBF 316L stainless steel fabricated using powders reused for up to 15 cycles. Contrary to the common assumption that oxygen and nitrogen uptake inevitably degrades structural integrity, the cryogenic yield strength increases markedly with reuse, rising from 600 MPa for virgin powder to 857 MPa after 15 reuse cycles, while the ultimate tensile strength remains comparable. Multiscale characterization reveals that powder reuse increases oxygen and nitrogen contents and raises the effective stacking-fault energy, thereby suppressing deformation-induced martensitic transformation that otherwise initiates along deformation-twin boundaries during 77 K deformation. In addition, reuse promotes the formation of fine oxide/nitride nano-dispersoids within the builds, which impede dislocation glide and enhance the initial resistance to plastic deformation, providing an oxide-dispersion-strengthening-like contribution. Overall, this study reframes powder reuse-induced chemical evolution from a degradation concern into a controllable design variable for in-situ dispersion strengthening, enabling more sustainable additive manufacturing while improving cryogenic structural performance.

This presentation introduces a novel class of compositionally complex steels (CCSs) developed by integrating high-entropy alloy (HEA) design principles into iron-based systems. These alloys utilize five major components (each >5 at. %), with iron as the primary constituent, to access previously unexplored phase regions. This design strategy facilitates a unique dual-nanoprecipitation microstructure consisting of simultaneously formed shearable carbides and non-shearable B2 particles. Utilizing atomic-scale characterization through Scanning Transmission Electron Microscopy (STEM) and Atom Probe Tomography (APT), we elucidate the complex precipitation kinetics and spatial distribution of these phases. The resulting CCSs exhibit an extraordinary mechanical properties, achieving ultrahigh specific tensile strengths of up to 260 MPa·cm³ g⁻¹ and exceptional ductility ranging from 13% to 38%. This performance synergy significantly outperforms conventional advanced lightweight steels and high-strength HEAs. Our analysis of dislocation-precipitate interactions reveals that the dual-nanoprecipitation drives flow stress to a critical threshold, triggering mechanical twinning. This activation of secondary hardening mechanisms provides sustained strain hardening and enhanced toughness. These findings provide a transformative framework for designing next-generation structural materials that require an excellent combination of density, strength, and formability.

Nanostructured metals typically suffer from catastrophic ductility loss, while gradient nanostructures, although promising, are often limited by thermal instability and poor scalability. Here, we overcome these challenges by introducing a thermomechanical-coupled incremental sheet forming strategy to engineer an oxide-mediated dual-gradient structure in a face-centered-cubic (FCC) nanostructured 316L stainless steel. The process imposes cyclic through-thickness thermomechanical gradients, generating a hierarchical structure with grain sizes spanning from ~40 nm at the surface to ~20 µm in the core. Concurrently, ultrahigh compressive stress and intense thermal input transform the inherent Cr-passivation film into dispersed nano-oxides penetrating ~30 µm in depth. These nano-oxides act as stabilizing skeleton that suppress thermal coarsening of nanograins while, counterintuitively, enhancing strain hardening within the strongest surface layer. In parallel, the cyclic thermomechanical loading induces dense dislocation dipoles in the mid-layers, which mitigate strain concentration in the soft regions. The resulting dual-gradient structure enables an unprecedented strain-hardening capability in GPa-level stable austenitic steel, overwhelming the regime dominated by hetero-deformation-induced (HDI) strengthening, while maintaining tensile ductility exceeding 40%. This work establishes a scalable pathway for designing nanostructured austenitic steels that simultaneously achieve high strength, sustained strain hardening, and large ductility.

Pure cobalt generally exhibits a hexagonal close-packed (HCP) structure at room temperature and is therefore known for its limited ductility and toughness. In the present study, we demonstrate that ultra-grain refinement can strongly stabilize the high-temperature face-centered cubic (FCC) phase, leading to the formation of metastable FCC pure cobalt with exceptional mechanical properties. By systematically refining the prior FCC grain size from 85 μm to 0.64 μm, the retained FCC phase fraction at room temperature increased dramatically from ~10% to ~89%.The ultrafine-grained (UFG) FCC cobalt exhibited a unique hierarchical microstructure consisting of ultrafine FCC grains containing dense stacking-fault (SF) networks together with HCP martensite plates containing numerous SFs and thin FCC layers. This heterogeneous defect architecture provided simultaneous strengthening and strain-hardening capability, resulting in a tensile strength exceeding 1 GPa together with tensile elongation above 35%, thereby overcoming the conventional strength–ductility trade-off of pure metals.In-situ synchrotron X-ray diffraction during tensile deformation revealed that grain refinement markedly promoted deformation-induced FCC→HCP martensitic transformation, leading to sustained transformation-induced plasticity (TRIP) hardening. Furthermore, ultra-grain refinement strongly suppressed premature void and crack formation, causing a transition in fracture behavior from brittle cleavage-dominated fracture to ductile void-coalescence fracture.These findings demonstrate that hierarchical ultrafine-grained microstructures and metastable phase heterogeneity can be effectively utilized to achieve outstanding strength–ductility synergy even in elemental metals, offering new insights into heterostructure design and TRIP-assisted deformation mechanisms in cobalt-based materials.

Achieving strength-ductility synergy remains a major challenge in magnesium (Mg) alloys. Conventional precipitation strengthening often improves strength but severely degrades ductility due to stress concentration caused by excessive precipitates. In this study, we introduced a high density of spherical dual-phase (DP) nanoprecipitates—consisting of coherent Mg₃Bi₂ and Mg₂Sn phases enveloped by an Ag/Zn segregation layer—into a dilute Mg-Bi-Sn-Ag alloy. Compared to the Ag-free alloy (which contains few DP nanoprecipitates), the Ag-containing alloy with abundant DP nanoprecipitates simultaneously achieves an 89% increase in elongation and a 26 MPa improvement in strength. The high density of DP nanoprecipitates arises from Ag-assisted precipitation of Mg₃Bi₂, followed by heterogeneous nucleation of Mg₂Sn on Mg₃Bi₂ substrates with an orientation relationship of {0001}Mg₃Bi₂∥{111}Mg₂Sn during thermomechanical processing. Beyond the conventional strengthening effect of precipitates blocking dislocations, in-situ TEM reveals that these high-density DP nanoprecipitates promote the activation of pyramidal dislocations at tri-phase interfaces. This activation is attributed to high stress concentration, terrace-ledge structures, and solute segregation at the heterogeneous interfaces. The dense DP nanoprecipitates also enhance dislocation interactions and entanglement, thereby improving the strain-hardening capacity of the Mg-Bi-Sn-Ag alloy and enabling simultaneous gains in tensile strength and elongation. This heterogeneous phase regulation strategy offers a feasible pathway for developing low-cost, high-performance Mg alloys.

Powder metallurgy (PM) provides a powerful route for designing heterogeneous and hierarchical material architectures, enabling the integrated control of feedstock characteristics, microstructural evolution, manufacturing behavior, and final properties. In particular, architecturally engineered powders allow interfaces, phase distributions, grain structures, surface chemistry, and reinforcement networks to be tailored across multiple length scales, expanding the design space for both conventional PM and advanced additive manufacturing.In this work, gas atomization was employed as a scalable rapid-solidification process to fabricate high-quality metallic powders for structural material systems, including high- and medium-entropy alloys, Al–Si alloys, super duplex stainless steels, Haynes 214, and NiCrAl-based alloys. The resulting powder characteristics, such as morphology, particle size distribution, sphericity, flowability, packing behavior, surface oxidation, and oxygen/moisture sensitivity, were systematically evaluated and correlated with subsequent spark plasma sintering, directed energy deposition, and powder bed fusion behavior. These powder-level characteristics strongly affected densification, powder feeding, laser–powder interaction, melt-pool stability, defect formation, and the structural and mechanical properties of the processed materials.Several heterogeneous structural concepts were demonstrated, including compositionally graded high-/medium-entropy alloy mixtures, layered architectures, harmonic structures, and B4C-reinforced CoCrFeMnNi high-entropy alloy composite powders for directed energy deposition. These approaches highlight how powder design and post-processing can be combined to improve microstructural uniformity, interfacial stability, and mechanical performance. In functional materials, Bi2Te3-based thermoelectric powders were also processed into textured multiscale microstructures for enhanced transport performance. Collectively, this work emphasizes heterogeneous and hierarchical powder architectures as a general PM framework for next-generation structural and functional materials.

To overcome the trade-off between strength and ductility, "heterostructure control" has emerged as a breakthrough strategy. This presentation outlines next-generation heterostructured materials fabricated via Liquid Metal Dealloying (LMD) and Liquid Metal Phase Replacement (LMPR). By thermodynamically controlling the heat of mixing, this unique metallurgical process achieves self-organized, nano- to micrometer-scale bicontinuous composite structures comprising phase-separating soft and hard phases. These materials exhibit unique mechanical properties, including upper-bound rule of mixtures compliance and anomalously low Young's moduli. We present our latest research results and discuss the scientific potential of bicontinuous composites.

Friction and wear, long regarded as unavoidable penalties in mechanical systems, consume nearly a quarter of global primary energy. Metallic components in engines, turbines, and bearings therefore present both the greatest challenge and the greatest opportunity for efficiency gains. This talk will show how heterostructured (HS) metals—encompassing gradient, laminate, and nanotwinned (NT) architectures—enable adaptive and self-stabilizing responses under diverse tribological conditions. Through engineered gradients in strength, periodic stacking of layers with distinct mechanical responses, and the incorporation of dense nano-twin populations, HS metals redistribute contact stresses, promote compatible heterogeneous plasticity, and delay the onset of surface degradation, leading to substantial reductions in friction and wear. Building on these mechanistic insights, we discuss a full-scaling tribological framework that links architectural descriptors to operational variables and to friction–wear responses from nano- to macro-scales. The convergence of heterostructure design with advanced fabrication routes is expected to yield microstructures that are not only strong and wear-resistant but also adaptive and robust under service-relevant conditions, pointing toward low-energy, long-life metallic friction interfaces. References: X. Chen* et al., Physical Review Letters 134, 166201 (2025). X. Chen* et al., Materials Research Letters 12, 8 (2024).

Shot peening was applied to Ti-Ni shape memory alloys, and its effects on corrosion resistance and strengthening were evaluated. The shot-peened specimens exhibited a heterogeneous microstructure near the surface, where an amorphous phase was formed, differing from the internal microstructure. This surface amorphization improved the corrosion resistance of the alloy. In addition, the formation of the amorphous layer and the increase in hardness near the surface contributed to enhanced resistance to functional degradation. In cyclic tests involving plastic deformation followed by recovery to the initial shape, the shot-peened specimens showed a tendency to maintain the shape memory effect even after an increased number of cycles. These results indicate that shot peening is an effective surface modification technique for improving both the corrosion resistance and functional durability of Ti-Ni shape memory alloys.

Nanocrystalline (NC) metals and alloys promise extraordinary properties, yet their instability and poor ductility have long impeded practical deployment. Here we employ Ultrasonic Shot Peening (USP) to create heterostructured surface layer in bulk 316L stainless steel (SS). Nanoindentation and micropillar compression tests reveal nanohardness of 6.2 GPa and yield strength of 2.1 GPa, which is nearly an order of magnitude above coarse-grained counterparts. The canonical strength-ductility trade-off and thermal instability of NC-316L SS are overcome by introducing uniformly dispersed nanoscale precipitates. These precipitates pin grain boundaries and interfaces, enabling ultrahigh strength, substantial room-temperature compressive ductility, and exceptional thermal stability. This combined stabilization and gradient heterostructure strategy offers a practical route to scalable, lightweight, and mechanically robust NC steels. Beyond fundamental insight into structure-property design, the approach opens opportunities for applications in advanced mechanical systems, bio-related devices, and radiation-tolerant components for nuclear engineering.

Carburizing and quenching is widely used for automotive components such as gears made of AISI 4120 steel because it improves surface hardness and fatigue strength. However, distortion generated during the quenching process often causes dimensional changes in components. To achieve high dimensional accuracy, additional finishing processes such as grinding are generally required after heat treatment, which increases manufacturing steps and production costs.To address these issues, this study proposes a heterogeneous surface-controlled carburizing and quenching process that combines anti-carburizing treatment with conventional carburizing and quenching. In this method, carburized regions on the surface are locally controlled using masking techniques to create a designed hardness distribution, aiming to reduce heat-treatment distortion.Experimental results showed that the proposed process successfully produced the intended hardness distribution on the specimen surface. The hardness distribution could be controlled by adjusting the geometry of the anti-carburizing mask. Furthermore, wear tests confirmed that sufficient wear resistance was maintained even when a heterogeneous hardness distribution was introduced.These results demonstrate that the proposed process is a promising approach for reducing distortion while maintaining required surface properties.

Multi-material additive manufacturing (MMAM) enables spatially controlled material composition within complex parts, thereby offering a powerful route to fabricate heterostructures. Additive manufacturing (AM), also known as three-dimensional (3D) printing, encompasses a family of fabrication techniques in which complex geometries can be built directly on a platform from a computer-aided design (CAD) file. These processes construct components point by point, line by line, or layer by layer, without the need for moulds or subtractive machining. Nevertheless, most commercially available AM systems are designed for single-material processing. MMAM is emerging as the next generation of additive manufacturing, capable of controlling both geometry and material composition, and represents a promising approach to realise heterostructures. In this talk, I will review the current state of the art in multi-material additive manufacturing, present our dry powder micro-dispensing technology developed for laser powder bed fusion (LPBF)-based AM, and discuss recent progress in fabricating heterostructures using MMAM.

The high-temperature applications of aluminum alloys are constrained by their poor thermal stability, high creep susceptibility, and limited strength at elevated temperatures. Traditional dispersion strengthening has encountered inherent limitations in overcoming these challenges. Here, we introduce a bioinspired nanoscale confinement strategy realized by engineering a continuous three-dimensional crystalline-amorphous interpenetrating network structure, reminiscent of those found in natural biological materials. This strategy is implemented in an additively manufactured aluminum alloy, providing stringent spatial confinement that effectively impedes dislocation motion, grain-boundary migration, and atomic diffusion. In addition to good printability, the as-printed alloy achieves ultrahigh strength at room temperature to elevated temperatures, superior creep resistance, and outstanding thermal stability – a synergistic combination of properties that markedly outperforms previously reported materials. This paper demonstrates the concept of strengthening materials by utilizing a continuous nanoscale amorphous network, rather than dispersed particles, through harnessing the nanoscale confinement effect inspired by Nature.

Laser additive manufacturing involves intrinsic rapid solidification rate and elemental segregation, which induce thermal residual stress and metastable microstructures, potentially leading to mechanical performance degradation. To address this, we evaluated stacking fault energy (SFE) and hierarchical precipitation to enable near-full recrystallization in a Ni-based multi-principal element alloy. Guided by phase diagram calculation and density functional theory, a heterostructured Ni-Cr-Fe-Co matrix with Al/Ti/V additions was designed and fabricated to stabilize a medium-level intrinsic SFE while forming hierarchical precipitates (primary BCC/B2 and secondary nanoscale acicular phases) via direct energy deposition in-situ alloying. Uniformly distributed precipitates nucleate preferentially within the grains, with limited formation at the boundaries. Consequently, the as-deposited alloy exhibited a yield strength of 790 MPa, ultimate tensile strength of 1164 MPa, and uniform elongation of 24.6 %, while multiscale characterizations confirmed plastic deformation interaction of precipitation within the recrystallized grains. This study demonstrates that engineering SFE and hierarchical heterostructures promote dynamic recrystallization and synergetic mechanical properties, offering a generalizable strategy for additively manufactured Ni-based alloys.

Aluminum alloys has become important for reduction of CO2 emissions and improvement of fuel efficiency. Among several types of aluminum alloys, Al-Mg-Si alloys used for body panels due to its good bake-hardening response. The age-hardening behavior is affected by the competitively formed nanoclusters during low temperature since heterogeneously formed nanoclusters are considered as the nuclei of the strengthening phase in Al-Mg-Si alloys. Nanolusters in Al-Mg-Si alloys are difficult to be characterized by the conventional transmission electron microscopy (TEM) since the atomic size is quite similar between Mg, Al and Si atoms. Atom probe tomography (APT), one of the useful techniques, was utilized to clarify the internal structure of nanoclusters, enabling quantitative analysis of cluster size, morphology, and chemical composition. Also, Monte Carlo simulation was carried out to understand the clustering behavior since the experimental approach provides the limited information. The age-hardening behavior during two-stet and multi-step heat treatment was studied. The precipitates formed with the different heat treatment histories were quantitively analyzed by the both TEM and APT.

Ferrite–martensite dual-phase (DP) steels exhibit an excellent balance between strength and ductility owing to their hetero-structures consisting of soft ferrite and hard martensite phases.  Although grain refinement is known to furthermore improve the strength–ductility balance of DP steels, the microstructural origin of the enhanced post-uniform elongation has not yet been fully clarified.  In the present study, the effect of grain refinement on local deformation behavior and damage evolution was systematically investigated using high-resolution digital image correlation (HR-DIC) technique combined with microstructural characterization for micro-void formation and growth.  DP steels with two different average ferrite grain sizes of 28.9 μm and 11.8 μm were prepared and tensile-deformed.  The DIC analysis clarified that the fine-grained DP steel exhibited more homogeneous strain distributions during tensile deformation, accompanied by larger plastic strains within martensite.  Although many micro-voids formed in the fine-grained specimen, most remained small even at fracture stage.  In contrast, the coarse-grained DP steel exhibited fewer micro-voids, but some of them underwent pronounced growth, leading to macroscopic fracture.  Strain mapping near the fracture region revealed that voids and cracks preferentially developed in regions exhibiting steep strain gradients.  The results indicate that the grain refinement suppresses severe strain localization and damage evolution by preventing void growth, thereby contributing to the improved post-uniform elongation.

The highly tunable properties of multi-principal element alloys, commonly known as high-entropy alloys (HEAs), provide a remarkable potential for the development of superior materials for critical structural applications that involve extreme conditions. In this talk, the effect of heterogeneous microstructure on mechanical properties of face-centered cubic (FCC) and body-centered cubic (BCC) HEAs at both cryogenic and elevated temperatures will be evaluated. Moreover, the speaker’s latest work for searching both FCC and BCC HEAs that possess superb mechanical properties across a broad range of temperatures will be presented. For FCC HEAs, multifunctional applications accompanying with various deformation and strengthening mechanisms over a broad temperature range will be discussed. For BCC refractory HEAs, the strategy of alloy design for super formability at ambient temperature and hetero-deformation induced strengthening for this alloy at both low and high temperatures will be shown. In the end, guidance for future development of hetero-structured HEAs at cryogenic-to-elevated temperatures will be provided. Enter description here.

This research aims to examine the effect of high-pressure heat treatment (HPHT) on additively manufactured IN625. The goal was to regulate the precipitation behavior and evolution of the microstructures under HPHT. The results obtained from HPHT were compared with those from conventional heat treatment. Unlike conventional hot isostatic pressing (HIP), HPHT maintains pressure throughout the cooling and aging stages. The samples were subjected to various pressure and temperature conditions following HIP to study the precipitation behavior. This allowed the study of pressure in suppressing the carbide precipitation and its effects on material properties. All treatments were completed in a single HIP cycle, reducing processing time while enabling effective microstructure control and property enhancement. Furthermore, the microstructure and properties of nickel-based superalloys fabricated by additive manufacturing, alloy modification, and advanced post-processing methods are also studied. The study starts with the investigation of a modified CM247 alloy, the CW247, with enhanced processability for laser powder bed fusion. Cracking susceptibility was mitigated with the compositional changes, but there was still a considerable amount of porosity and surface-connected cracking in the as-built material. With a conventional HIP process, pressures of 100 MPa and 150 MPa were not sufficient to completely remove the defects. With further processing parameters, the cracks were reduced, and subsequent HIP and HPHT resulted in densification and structural integrity of the treated material, with most of the remaining porosity being eliminated.

Face-centered cubic (FCC) high entropy alloys (HEAs) are increasingly recognized for their outstanding mechanical performance, yet their behavior under extreme dynamic loading conditions remains a frontier of research. Here we reveal that a select group of FCC HEAs exhibit an exceptional combination of strain hardening and strain-rate hardening that persists to very large strains and ultrahigh strain rates, rendering them ultrastrong under impact. High-strain-rate compression tests show that the flow stress rises dramatically with increasing strain and strain rate, far exceeding the quasi-static strength, while pronounced positive strain-rate sensitivity suppresses plastic instability. This sustained hardening response delays localization and enables the material to absorb substantial energy before failure. Laser-driven spall experiments demonstrate that these alloys possess a remarkably high damage tolerance under shock loading. The measured spall strength reaches values that surpass those of conventional high-performance structural alloys, approaching a substantial fraction of the ideal tensile strength. Post-mortem microstructural analysis indicates that homogeneous and extensive plastic deformation distributed throughout the microstructure effectively disperses tensile stress waves, inhibiting void nucleation and coalescence. More importantly, heterogeneous microstructure engineering enhance the impact resistance by providing additional strengthening effect. The combined attributes, ultrahigh dynamic flow stress, exceptional spall resistance, and suppressed localized failure, position FCC HEAs as prime candidates for applications in armor, blast mitigation, and aerospace components subjected to extreme impulsive loads.

An austenitic stainless steel AISI 304 plate was functionally graded by interstitial alloying with nitrogen by high-temperature solution nitriding, resulting in a symmetrical nitrogen concentration profile over the plate thickness. This leads to a depth-gradient in the austenite stability. The responses to plastic deformation and austenite stability were investigated by applying cold rolling up to 70 pct overall thickness reduction of the plate. The evolutions of nitrogen concentration profile, phase distribution, deformation microstructure, and hardness developing upon plastic deformation were revealed. In addition, the functionally graded steel enables the elucidation of the correlation between nitrogen content and corrosion resistance over a continuous range of nitrogen contents by means of electrochemical analysis, i.e. starting from different depths on the graded steel as realized by successively removing thin layers by gentle polishing. The results demonstrate that the critical nitrogen content necessary to prevent deformation-induced martensite formation increases in the low-to-medium strain range, while it dramatically increases at high strain levels. With increasing nitrogen content, the dominant deformation mode evolves from deformation-induced martensite formation to a mixture of martensite and twin formation, and, eventually twinning and dislocation glide. Depth-dependent corrosion resistance depends strongly on nitrogen content and the associated plastic deformation regimes.

The transition toward a hydrogen energy society has heightened the importance of alloys for hydrogen storage. Liquid hydrogen, stored at extremely low temperatures (~20 K), requires alloys that retain reliable mechanical performance in cryogenic environments, where properties can change markedly. Understanding the deformation and fracture behavior of materials under these conditions—together with advances in the analytical techniques used to characterize them—is therefore critical to ensuring the stability of hydrogen storage systems.In tensile testing of Al alloy at room temperature, however, they exhibit flow instability associated with the Portevin–Le Chatelier (PLC) effect, which degrades elongation. At liquid nitrogen temperature (77 K), serration is markedly suppressed, yielding higher strength and ductility. This behavior points to the potential of aluminum alloys for cryogenic service, including at 20 K.Digital image correlation (DIC) is a powerful method for visualizing and quantifying deformation by tracking speckle patterns applied to the specimen surface. In cryogenic environments, however, phenomena such as adiabatic heating can generate bubbles that disrupt accurate pattern tracking.We designed a cryogenic chamber that enables DIC under such extreme conditions. Using liquid nitrogen, we performed DIC and mitigated these technical challenges by integrating machine learning. The deformation and fracture behavior of Al 5182 alloy was examined from room temperature to cryogenic temperatures. Complementary microstructural observations were carried out to clarify the governing mechanisms. These findings are expected to deepen understanding of material behavior under extreme cryogenic conditions.

In this study, multiple-phases AlCoCrFeNi multi-principal element alloys were synthesized by spark plasma sintering (SPS) to investigate the effect of microstructure on creep properties. To obtain different microstructure, SPS were conducted at 1000℃, 1100℃ and 1200℃. In addition, three powders with mean particle diameters of 14.6, 41.9 and 82.4 μm were used to examine the influence of powder particles size on creep properties. Creep tests were conducted at 700℃ in air. The specimen SPS at 1000℃ consisted of a B2 matrix, BCC precipitates, σ phase and irregularly shaped FCC phase. In contrast, the specimens SPS at 1100℃ and 1200℃ consisted of a B2 matrix containing fine BCC precipitates and FCC phase along the grain boundaries, although the FCC morphology differed between the two specimens. The creep test results indicated that creep life increased with increasing of SPS temperature at the same applied stress, whereas the mean powder particle size had little effect on the creep life. Microstructural observation results for crept specimens demonstrated that creep crack initiated and propagated along prior particle boundaries for 1000℃ SPS specimens, because low sintered temperature led to weak interparticle bonding. In contrast, for 1100℃ and 1200℃ SPS specimens, crack initiated at FCC/B2 matrix interfaces. For 1200℃ SPS specimens tested under 150 and 100 MPa, creep-assisted B2 precipitates were observed within the FCC phase. The creep life of 1200℃ SPS specimens were comparable to that of AlCoCrFeNi2.1.

Additively manufactured (AM) metallic lattice structures provide significant opportunities for the lightweight design of components with complex geometries, owing to their excellent mechanical performance and energy absorption capacity. The compressive mechanical behaviours of lattice structures have been extensively investigated with cubic specimens containing various unit cell topologies. The tensile mechanical responses of lattice structures remain not well understood, as the traditional design of tensile specimens with solid heads and uniform lattice-structured gauge sections usually causes damage and fracture adjacent to the clamped heads due to stress localisation. Furthermore, the effects of AM microstructures on the mechanical performance of different lattice structures have not yet been fully revealed.In this work, gradient lattice structures of 316L stainless steel with spatially varying porosity were manufactured by laser powder bed fusion, incorporating four distinct unit cell topologies of face-centred cubic (FCC), body-centred cubic (BCC), triply periodic minimal surface (TPMS) diamond, and TPMS gyroid. The mechanical performance, the structural deformation, and the microstructural evolution of the gradient lattice structures were investigated under uniaxial tensile loading. An anisotropic plasticity and damage model was developed to capture the stress-strain responses of the gradient lattice structures during the deformation. The results reveal that dislocation cells within the lattice structures play a crucial role in strengthening during deformation. Compared to the gradient FCC and BCC lattices, the gradient TPMS diamond and gyroid lattices with smooth surface transitions significantly alleviated stress localisation and enhanced the mechanical performance, offering valuable insights for innovative design of high performance and lightweight components.

Electropulsing (EP) treatment, as an ultrafast and non-equilibrium processing technique, has demonstrated unique capabilities in tailoring the microstructures of metallic materials in a manner different from conventional thermomechanical routes. In this study, 75% cold-rolled CoCrNi-based medium-entropy alloys (MEAs) were selected as model materials to investigate the effects of EP parameters on the evolution of heterogeneous microstructures and mechanical properties. Through the coupling of EP-induced ultrafast precipitation and recrystallization processes, heterostructure design was successfully realized. With a relatively low current density (510 A/mm2), σ phase precipitation within shear bands introduced significant microstructural heterogeneity, enabling the CoCrNi-based MEA to achieve a tensile strength of 1629 MPa; whereas with a higher current density (700 A/mm2), pronounced recrystallization occurred in the alloy. Based on this experimental finding, a two-step treatment strategy was developed for the CoCrNi-based MEA. In the first step, continuous pulses with a low current density were employed to promote σ phase precipitation, while in the second step, cyclic pulses with a high current density were applied to induce recrystallization. This process constructed a heterostructure composed of recrystallized grains, deformed grains, and heterogeneously distributed σ precipitates. Such a heterogeneous architecture promoted strain partitioning and synergistic deformation, while the σ phase provided strengthening and stabilized the heterostructure through grain boundary pinning. The resulting alloy exhibited an enhanced strength-ductility balance. This work demonstrates that precipitation-assisted heterogeneous structural design offers a promising pathway for mechanical property optimization in MEAs.

Non-oriented silicon steel is a representative soft magnetic material used in electric motor cores because of its high magnetic flux density, low iron loss, and relatively isotropic magnetization behavior in the sheet plane. Silicon addition increases electrical resistivity and reduces energy loss (iron loss), while favorable crystallographic textures such as //ND contribute to improved magnetic performance. Nevertheless, iron loss is inevitably generated during motor operation due to microstructural and dimensional factors that obstruct magnetization and demagnetization. Iron loss consists of hysteresis loss and eddy current loss, including classical and anomalous components. To reduce eddy current loss, thin-gauge electrical steels with thicknesses below 250 μm have been actively developed. As the sheet thickness decreases, however, the influence of the surface and subsurface regions on the overall magnetic properties becomes increasingly important. Since the surface microstructure is strongly affected by the final annealing atmosphere, investigating surface microstructural effect on iron loss is essential for further improving thin-gauge non-oriented silicon steel.In this study, non-oriented silicon steels with different surface and subsurface microstructures were prepared by varying the fraction of nitrogen and hydrogen during final annealing. The surface layer, interfacial roughness, and near-surface inclusions were analyzed, and their relationship with iron loss was investigated. The results provide insight into how final annealing atmosphere controls surface microstructural evolution and, consequently, the magnetic performance of thin-gauge non-oriented silicon steel.

Collaboratively improving surface wear and corrosion resistance has long been a core issue in metallic protection. This work utilized laser cladding to fabricate a TiN-reinforced MHEA composite coating on 17-4PH stainless steel, aiming to simultaneously enhance its service performance. Microstructure analysis shows that the introduction of nano TiN not only significantly refines the coating grains, but also promotes the in-situ formation of heterostructure (MnTi₂O₄+9R) @TiN core-shell precipitates in the coating when added in moderation. Compared to the substrate, the optimal content of 2TiN coating reduces the corrosioncurrent density and wear rate by 54.9% and 81.8%, respectively. The enhanced corrosion resistance is attributed to improvement of the uniformity and stability of the passive film induced by grain refinement, as well as the immobilization of Mn within stable core–shell nanoprecipitates. Meanwhile, the improved wear resistance arises from grain refinement, contact stress dispersion by the precipitates, and phase-transition-induced hardening.   Key words: Laser cladding, TiN, Heterostructure precipitates, Corrosion, Wear.

The slow kinetics and rapid degradation of oxygen reduction reaction (ORR) activity at polymer electrolyte membrane fuel cell (PEMFC) cathodes remain major barriers to the large-scale deployment of fuel cell electric vehicles. Developing electrocatalysts that combine high activity with long-term durability is therefore crucial for practical fuel cell applications. In this study, we introduce a new class of highly ordered platinum–cobalt (PtCo) alloy nanoparticles with well-defined cobalt nitride decorated in the L10-PtCo intermetallics. The resulting intermetallic core-shell catalyst exhibits an outstanding initial mass activity of 0.88 A mgPt–1 at 0.9 V, retaining 71% of its activity after 30,000 potential cycles, along with only a 9% loss in electrochemical active surface area, surpassing the US Department of Energy 2025 targets, demonstrating exceptional durability under realistic operating conditions. We reveal that precise control of atomic ordering within the core produces an optimized lattice structure that markedly enhances ORR kinetics. Furthermore, strong interactions between cobalt and incorporated nitrogen increase the energy barrier for cobalt dissolution, thereby ensuring superior catalyst stability. Overall, this work presents a comprehensive structural engineering strategy for Pt-based electrocatalysts, offering a viable pathway toward highly efficient, low Pt-loading PEMFC cathodes suitable for practical applications. .

Few-walled carbon nanotubes (FWCNTs), typically comprising three concentricgraphene walls, combine the high electrical conductivity of single-walled (SWCNTs)with the mechanical robustness of multi-walled CNTs (MWCNTs). They exhibitintermediate structural and electrical properties between those of SWCNTs andMWCNTs, while maintaining tunable porosity and structural stability. In this study, wesystematically investigated the electrochemical performance of high-purity, submillimeter-long SWCNTs and FWCNTs, synthesized via fluidized-bed chemical vapordeposition, and employed as conductive agents in Si/graphene oxide (Si/GO)composite anodes for Li-ion batteries (LIBs). Acid-assisted oxidation followed by mildbath-type sonication was optimized to enhance aqueous dispersibility without inducingsignificant tube shortening or crystallinity loss. This controlled treatment enabled theformation of continuous, low-resistance conductive networks within the Si/GOcomposite anodes. Among all tested conductive agents—including probe-sonicatedFWCNTs, SWCNT-based analogues, and commercial carbon black (Super P)—bathsonicatedFWCNTs exhibited the optimal electrochemical performance, achieving thehighest initial Coulombic efficiency (70.7%), high rate capability (452.8 mAh/g at 0.2A/g), excellent long-term cycling stability over 200 cycles, and lowest charge-transferresistance (15.4 Ω) after extended operation. The enhanced performance originatesfrom the long-tube morphology and multi-walled structure of the FWCNTs, whichpreserve their inner-wall crystallinity even after acid oxidation, ensuring durable anduniformly dispersed conductive networks. These findings establish sub-millimeter-long

Designing heterogeneous structures in functional materials often leads to significant enhancement of their functional properties. These heterogeneous structures span multiple length scales, ranging from the micrometer scale to the nanoscale. Among them, nanoscale heterogeneity has a particularly strong influence on functional properties because local variations in composition, strain, interfaces, and atomic ordering can critically affect functional properties such as electronic, magnetic, thermal and catalytic behaviors. Therefore, understanding these nanoscale variations is essential for establishing structure-property relationships and improving overall material performance. In this context, atom probe tomography (APT) has emerged as a highly effective characterization tool for probing nanoscale heterogeneity through three-dimensional (3D) atomic-scale imaging and quantitative compositional analysis. With its sub-nanometer spatial resolution and ultra-high chemical sensitivity at the parts-per-million (ppm) level, APT is particularly well suited for analyzing local chemical fluctuations and interfacial features in complex materials. Owing to these unique capabilities, APT has been extensively utilized in a wide range of material systems, including metallic alloys, semiconductors, oxides, and biomaterials, to elucidate structure-property correlations. In this presentation, representative case studies demonstrating the application of APT in functional materials research will be introduced.

The photocatalytic conversion of renewable resources into green energy carriers, including hydrogen (H2) and methane (CH4), offers a promising approach for mitigating energy shortages and environmental challenges. In this study, a highly efficient photocatalyst was developed by constructing a P/N heterojunction based on a high-entropy oxide (HEO) using high-pressure torsion (HPT) and annealing (Fig. 1). The P-type semiconductor CuO was combined with an N-type HEO composed of d0 metal cations (Ti, Zr, Nb, and Ta) and a d10 cation (Zn) to promote charge separation and transfer.The resulting heterostructure exhibited improved photo-response characteristics, including enhanced visible-light absorption, accelerated carrier migration, and suppressed electron–hole recombination. By integrating atomic-level d0/d10 electronic interactions with microscale P/N heterojunction engineering, the photocatalytic activity for both water splitting and CO2 methanation was significantly improved. After optimizing the vacancy concentration within the heterojunction, the catalyst achieved an H2 evolution rate of 0.71 mmol.g⁻1.h⁻1 via photocatalytic water splitting (Fig. 2) and a CH4 production rate of 2.40 μmol.g⁻1.h⁻1 via CO2 reduction (Fig. 3), with a methanation selectivity of 72%.This work, published in [2], demonstrates an effective materials design strategy for constructing advanced heterostructured photocatalysts for sustainable fuel generation

The development of non‑precious metal electrocatalysts for the oxygen evolution reaction is critical for water electrolysis technologies. In this work, we demonstrate a combined strategy of thermomechanical processing and dealloying to enhance the OER performance of FeMnCrNi high‑entropy alloys. Specifically, thermomechanical treatment consisting of cold rolling followed by annealing at 800 °C was applied to construct a heterogeneous microstructure comprising a primary matrix and uniformly dispersed Cr‑rich secondary phases. This compositional and structural heterogeneity enables the fabrication of a hierarchically porous architecture with abundant exposed active sites and an optimized electronic structure. Electrochemical tests reveal that the resulting catalyst exhibits exceptional OER activity, delivering a low overpotential of 290 mV at 10 mA cm⁻² and a small Tafel slope of 48 mV dec⁻¹ in alkaline electrolyte, outperforming commercial noble‑metal oxide electrocatalysts. To gain deeper insight into the origin of the enhanced OER performance, density functional theory calculations were performed to investigate the surface reconstruction induced by dealloying. The theoretical overpotentials for oxygen-containing intermediate adsorption on the reconstructed active sites were calculated, revealing a significantly reduced energy barrier compared to the pristine alloy surface. Furthermore, crystal orbital Hamilton population analysis was employed to evaluate the bond strength between surface active sites and the key intermediates. The results demonstrate that dealloying‑induced surface reconstruction optimizes the adsorption energetics. The experimental and computational findings elucidate the synergy of thermomechanical and dealloying enhancing catalytic activity effectively. This work highlights the potential of this scalable pathway for developing advanced high entropy alloy OER electrocatalysts.

Lithium–sulfur (Li–S) batteries promise high energy density, but parasitic reactions between the lithium anode and dissolved polysulfides drive severe interfacial corrosion that limits cycle life. Here we show, using atomistic simulation, that lithium-alloy anodes counter this degradation by spontaneously organizing the electrode–electrolyte boundary into composition-dependent heterostructured interphases — heterogeneous nanoscale zones whose strong chemical and structural gradients passivate the interface. Combining density functional theory with molecular dynamics driven by an M3GNet machine-learning potential, we sampled over 400 alloy–electrolyte configurations for each Li1−xMx (M = Mg, Al, Zn) solid solution built from special quasi-random structures, in contact with polysulfides, solvent, and salt. Interphase chemistry was resolved through DDEC6 bond-order analysis, lithium-displacement statistics, and S–S bond retention. A pure lithium anode develops a porous, unstable layer with facile Li migration and severe polysulfide decomposition. Alloying instead generates two distinct heterostructure types: in Li–Mg, magnesium co-migrates with lithium to assemble a chemically robust, Mg-enriched solid-electrolyte interphase (a chemical heterolayer), most effective at dilute substitution (x = 0.05); in Li–Al and Li–Zn, strong metal–metal interactions drive surface segregation into dense, few-atomic-layer gradient barriers (a physical heterostructure) that block polysulfide transport and arrest Li migration, optimal at higher alloying (x ≥ 0.5). Both mechanisms synergistically suppress lithium loss and preserve S–S bonding, yet through fundamentally different gradient architectures. These results establish atomistic design rules linking alloy composition to self-assembled hetero-interphase function, offering a route to interface-engineered, corrosion-tolerant anodes for durable Li–S batteries.

Harmonic structured (HS) multi-materials are characterized by a unique heterogeneous microstructure consisting of a continuous three-dimensional network (shell) of one metallic phase surrounding dispersed major regions (cores) of another. This architectural design enables the strategic spatial distribution of dissimilar metals to achieve synergistic properties. In this study, various HS multi-materials were fabricated via mechanical milling (MM) followed by spark plasma sintering (SPS). The microstructural evolution, as well as the mechanical and thermal properties, were investigated in detail. In Mo/Cu HS multi-materials designed for thermal management, a significantly lower coefficient of thermal expansion (CTE) was achieved while maintaining superior thermal conductivity compared to conventional particle-dispersed Mo/Cu composites. The continuous Mo-rich shell effectively provides a mechanical constraint against the thermal expansion of the Cu-rich core, successfully overcoming the inherent trade-off between low CTE and high thermal conductivity. Furthermore, the HS strategy was applied to high-performance tool materials, where a WC-Co shell provides high wear resistance while the high speed steel (HSS) cores enhance toughness. This material exhibits excellent wear resistance that surpasses the linear rule of mixtures. Notably, the impact energy density to fracture of the HS multi-material was approximately twice that of a monolithic WC-Co. Such improvements are attributed to the effective crack deflection induced by the heterogeneous HS architecture. In summary, harmonic structure control is a versatile and powerful strategy for tailoring multi-material systems, offering a new paradigm for overcoming performance trade-offs in advanced engineering materials.

Metallic alloys with optimal strength-ductility synergy, wear resistance, and corrosion resistance are essential for extreme service conditions to ensure enhanced safety and longevity. Traditionally, crystalline metals are known for their ductility but suffer from low strength and wear resistance, whereas amorphous metals exhibit high strength but are prone to brittleness. This study introduces a novel crystalline-amorphous dual-phase heteronanostructure, synergistically combining these contrasting properties to produce ultra-strong metals without sacrificing ductility. The advanced heteronanostructure encapsulates nanocrystals within thick amorphous grain boundaries, promoting cooperative co-deformation and reducing the risk of localized or galvanic corrosion. Employing state-of-the-art additive manufacturing techniques such as laser surface processing and magnetron sputtering, we have fabricated these unique heteronanostructured metals. Their mechanical behaviors, including deformation and wear mechanisms, were thoroughly examined through in situ SEM micropillar compression tests, mechanical wear testing at varying temperatures, and comprehensive atomic-scale characterizations. Furthermore, this study utilized atomistic simulations and theoretical modeling to elucidate the underlying plasticity and wear pathways, offering insights into the enhanced performance of these materials. These combined properties make the developed materials highly suitable for applications requiring robust, durable, and corrosion-resistant materials, setting a new standard for the design of next-generation metallic materials. Acknowledgements: HK RGC grants (PolyU15210123 and PolyU15201424), Hong Kong Innovation and Technology Commission (ITC) Guangdong-Hong Kong Technology Cooperation Funding Scheme (Nos. GHP/267/22GD and GHP/088/23GD), and Lai Yun Yin Second Charitable Foundation (N-ZHBK).

Heterostructure engineering has emerged as a powerful strategy to bypass the fundamental limits of conventional homogeneous materials. In fields such as aerospace, electric vehicles, and defense, there is an urgent demand for advanced metal matrix composites (MMCs) that simultaneously possess exceptional mechanical strength, high conductivity, and thermal stability. However, traditional MMCs are severely constrained by the classic strength-ductility trade-off and high-temperature degradation driven by uncontrolled intermetallic diffusion. To address these challenges, this study introduces a novel multi-layered heterostructural design that integrates axially continuous graphene (ACG) as a functional interstitial layer between disparate metallic matrices. By leveraging heterostructural synergy and effective interfacial control, the fabricated ACG-Ni wires successfully break the conventional strength-ductility trade-off, achieving a remarkable 71.76% increase in ultimate tensile strength along with a 58.24% enhancement in failure strain compared to pure nickel. Furthermore, the unique Ni-G-Cu heterostructure acts as an effective diffusion barrier, yielding a 307.6% higher electrical conductivity and a 61.2% higher current density limit than conventional Ni-coated copper after annealing at 650°C. Demonstrating extreme thermal resilience, an expanded Ni-Ag-G-Cu multi-layered heterostructure maintains its electrical integrity up to 850°C. These findings demonstrate that graphene-metal heterostructure engineering provides a highly scalable and robust platform for developing next-generation multifunctional materials capable of enduring extreme structural and thermal loads.

Gradient nanostructured (GNS) metals are emerging as promising candidates to overcome the persistent strength-ductility trade-off in structural materials. Despite their potential, systematic guidelines for microstructure design remain limited. In this work, a crystal plasticity finite element method is employed to quantitatively elucidate the effects of critical microstructural parameters on the mechanical behavior of GNS metals. The investigated parameters include the gradient ratio, the thickness ratio between the gradient and coarse-grained layers, and grain morphology (equiaxed versus lamellar). Comprehensive simulations enable quantitative assessment of how these parameters govern the synergy between strength and ductility. Results reveal that an intermediate gradient ratio and a well-balanced thickness ratio yield an optimal combination of strength and ductility. In terms of grain morphology, lamellar grains display increased strength, whereas equiaxed grains achieve superior overall mechanical performance. The mechanisms underlying these enhancements are elucidated through analyses of stress-strain gradient distribution, shear texture-induced stress redistribution, the evolution of stress states as characterized by the Lode parameter, and the mitigation of surface roughening. This study establishes a theoretical framework to guide microstructural design and process optimization in gradient nanostructured metals, advancing their application in high-performance engineering systems.

Heterogeneous microstructural design has been proven to be an effective strategy in breaking the strength–ductility dilemma in nanostructured metals. However, the precise control of heterogeneous microstructures to achieve strength–ductility synergy remains challenging. Here, we demonstrate a novel powder metallurgy approach for creating three-dimensional (3D) core–shell nanostructures with highly tunable shell thickness and grain size distributions. These 3D nanostructures enable superior strength–ductility synergy in metals, pushing the boundary of the Ashby map to unchartered territory. A combination of microstructural characterization, atomistic simulations and crystal plasticity modeling reveals that the generation and accumulation of geometrically necessary dislocations near the core–shell interface play a pivotal role in accommodating the strain gradient and sustaining a high strain-hardening rate during plastic deformation. Our work provides a viable approach for designing bulk nanostructured materials with 3D heterogeneous ingredients and demonstrates a promising pathway for the development of strong and ductile materials. Keywords: Harmonic structure; Three-dimensional core-shell nanostructures; Strength-ductility synergy; Geometrically necessary dislocations

Atherosclerosis, which narrows coronary arteries and reduces blood flow, is mostly treated with percutaneous coronary intervention (PC) using coronary stents. However, conventional polymer coatings used in drug-eluting stents (DES) are unsuitable for biodegradable DES systems due to poor elasticity and adaptability to damage during PCI and long-term application. In this study, we developed a biodegradable self-healing polyurethane (PU) elastomer for biodegradable coronary stent coatings. The PU elastomer exhibited excellent elastic recovery under large deformation (~ 300 % tensile strain), enabling structural integrity during stent crimping and balloon expansion. Additionally, it demonstrated autonomous self-healing under a blood-rich environment ( ≈ 81 % within 4 h and complete healing within 24 h), thus allowing the recovery of fatigue-induced defects. When applied to biodegradable magnesium (Mg) stents, the PU coating maintained coating integrity during crimping-expansion and exposure to physiological environment, while effectively suppressing hydrogen evolution, indicating controlled degradation behavior. Moreover, the PU coating serve as a drug-delivery platform by incorporating therapeutic nanoparticles (NPs), which were released from the matrix and maintained the ROS scavenging activation. Therefore, the biodegradable self-healing PU can function as a degradation-controllable functional coating material for biodegradable coronary stents.  *This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (Grant No. RS-2022-NR068191).

WC-Co cemented carbides are dominant cutting tool materials. Their hardness-toughness trade-off has been a long-standing dilemma that limits their performance. Here we report a heterostructuring strategy that simultaneously enhances their hardness and toughness, as demonstrated in a heterostructured WC-8 wt.% Co cemented carbide with a bimodal Co distribution, consisting of microscale soft Co domains embedded in WC-rich hard domains. Compared with conventional cemented carbides of the same composition, the heterostructured sample achieves simultaneous improvements in Vickers hardness, fracture toughness and transverse rupture strength. The WC-rich hard domains provide ultrahigh hardness, while the microscale soft Co domains plastically deform by partial dislocation slip and facilitate FCC to HCP phase transformation to release local stresses. Furthermore, the microscale soft Co domains developed back stress to maintain high strength, and also deflect, arrest and bridge cracks to increase the fracture toughness. Consequently, the heterostructured cemented carbide promoted high-energy trans-binder ductile tearing and transgranular WC fracture, which significantly enhanced the toughness without sacrificing the hardness and strength.

Grain boundaries (GBs) are usually in a metastable state and contain various types of ledges in heterostructured materials. The presence of these structural features may lead to heterogeneous solute segregation at nearly flat GBs in Al alloys and affect the mechanical properties of materials. In this study, the effects of GB structural features on solute segregation and dislocation nucleation are investigated by hybrid Monte Carlo and molecular dynamics simulations. The results demonstrate that local GB structural transitions and GB ledges result in the heterogeneous segregation of solutes Cu and Mg. The solute density at the GB is determined by the average segregation energy in different regions. Local structural transitions and ledges at GBs intensify strain localization, and result in a lower nucleation stress for dislocations compared to the ground-state GBs. A low concentration of the solute Cu tends to promote dislocation nucleation when it segregates at ground-state GBs, but inhibits it in other types of GBs. Conversely, the segregation of solute Mg promotes dislocation nucleation at all GBs. This difference is attributed to the effect of solute segregation on GB disorder. Increased GB disorder generates a stress gradient that provides an additional driving force for the atomic shuffling and free volume migration required for dislocation nucleation. Therefore, a negative correlation has been identified between GB disorder and dislocation nucleation stress.

Precipitation hardening plays a key role in strengthening Cu-Ni-Si alloys, where homogenization followed by cooling promotes the formation of Ni2Si precipitates in the Cu matrix. While a high density of fine precipitates improves strength, heterogeneous nucleation at grain boundaries (GBs) can produce irregularly shaped particles that degrade performance. In contrast, recent experiments by Han et al. showed that Mn addition changes the GB precipitation behavior, leading to improved mechanical properties with film-shaped Mn6Ni16Si7 (G-phase) precipitates at GBs instead of Ni2Si.Here, we combine first-principles density-functional theory (DFT) and machine-learning interatomic potential (MLIPs) calculations to understand the distinct precipitation behaviors of Ni2Si and G-phase in Cu-Ni-Si alloys without and with Mn addition. The irregular morphology of Ni2Si precipitates at grain boundaries (GBs) can be well explained by orientation- and position-dependent interfacial energetics. For Ni2Si, fully strained particles form a coherent Cu(110)//Ni2Si(100) interface, whereas partial strain relaxation leads to semi-coherent structures. Upon further strain release, out-of-phase atomic matching across the interface can generate repulsive zones and open-boundary-like structures at GBs. In contrast, Cu/Mn6Ni16Si7 interfaces are incoherent but show weak orientation dependence of interface energy, consistent with the experimentally observed film-shaped G-phase precipitates bridging differently oriented Cu grains. These results demonstrate that MLIP-based large-scale modeling provides a predictive framework for linking interphase-boundary structure to grain-boundary precipitation morphology in Cu alloys.

In response to the urgent demand for advanced aluminum alloys with high strength and high toughness in high-end equipment fields such as aerospace, this study establishes a high-throughput database of aluminum alloy precipitate structures based on the concept of materials genome engineering. Combining multi-scale simulation and machine learning methods, the intelligent design and mechanical behavior of novel advanced aluminum alloys are systematically investigated. Multi-model comparison and screening reveal that the XGBoost algorithm delivers the optimal prediction performance for alloy mechanical properties, which can accurately correlate heterogeneous structural characteristics including the morphology and distribution of the second phase as well as grain boundary features with macroscopic mechanical properties such as tensile strength and elongation. Aiming at the coordinated improvement of strength and toughness, a high-performance heterostructured aluminum alloy system is obtained through inverse design by integrating the machine learning prediction model with the particle swarm optimization (PSO) algorithm. Mechanical mechanism analysis indicates that the optimized alloy achieves synergistic strengthening and toughening via controllable dispersed precipitation of the second phase and grain boundary structure optimization. It effectively hinders dislocation movement, improves grain boundary bearing capacity, significantly restrains brittle fracture, and realizes the synchronous enhancement of strength and toughness. By integrating artificial intelligence algorithms, heterostructure regulation and grain boundary engineering technology, this work provides a theoretical basis and an innovative research paradigm for the rapid research and development as well as engineering application of advanced metallic materials in high-end fields.

Heterogeneous metal materials have excellent mechanical properties and great application potential in key engineering fields. Among them, grain size heterogeneous materials have become a research focus in this field. Such materials exhibit a bimodal grain size distribution, including fine-grained hard regions and coarse-grained soft regions, and the heterogeneity of these materials directly regulates their mechanical responses. . Thus, revealing grain size strengthening mechanisms is crucial for their optimization. The Hall-Petch relationship (1950s) quantifies this strength increment, with its applicability verified by extensive research. A large number of models (including pile-up, step, and sliding models) have been developed to explain and elucidate the form of this relationship, and recent studies have focused on the physical nature of the fitting constants in these models. However, despite extensive research on these models, their applicability varies significantly, with disparate fitting results lacking a unified comparable standard. Considering diverse experimental conditions and alloy types, accurate prediction of the Hall-Petch relationship remains challenging. To tackle this issue, the present study integrated data from over 20 pure metals/alloys to conduct data-driven modification of the Hall-Petch relationship via machine learning combined with dimensional analysis, providing references for its improvement and the development of new heterogeneous material constitutive models.

The hot deformation behavior of eutectic heterostructured multicomponent alloys is critical for optimizing thermomechanical processing and workability. In this study, the flow behavior of a eutectic heterostructured Ni–Cu–Co–Ti–Ta alloy was investigated using hot compression experiments, constitutive modeling, artificial neural network (ANN) prediction, and finite element analysis (FEA). The alloy exhibited an activation energy of approximately 257 kJ mol⁻¹ at a true strain of 0.65, indicating favorable hot workability. A strain-compensated constitutive model and an ANN model were developed to predict flow stress under different deformation conditions, with the ANN demonstrating superior predictive accuracy. Furthermore, FEA was employed to analyze stress, strain, and temperature distributions during deformation. The integrated experimental–computational framework provides valuable insight into the hot deformation behavior and processing optimization of eutectic heterostructured multicomponent alloys.

Understanding the relationship between microstructure and mechanical properties is essential for the design and optimization of structural materials. In recent years, deep learning approaches have been increasingly applied to predict material properties directly from microstructure images. However, image-only models often provide limited physical interpretability.In this study, a hybrid deep learning framework was developed for hardness prediction of forged Ti-6Al-4V alloy using optical microstructure images and lamellar spacing information. To quantitatively characterize the lamellar microstructure, an automated measurement program was developed to determine lamellar spacing from microstructure images. The measured spacing values were then incorporated as additional input features together with image data.Microstructure images acquired at ×200, ×500, and ×1000 magnifications were used to construct the dataset. Image features were extracted using a ResNet-50-based CNN model and combined with lamellar spacing information to predict hardness.Furthermore, SmoothGrad was employed to identify the microstructural regions contributing to hardness prediction. The visualization results indicated that the model focused on lamellar boundaries, orientation patterns, and spacing-related characteristics, demonstrating that physically meaningful microstructural information was incorporated into the learning process.The proposed approach provides a framework for integrating quantitative microstructural parameters with image-based deep learning and offers a practical strategy for investigating microstructure–property relationships in Ti-6Al-4V alloys.

We systematically investigate the solidification microstructure and elemental segregation behavior of Inconel 738LC fabricated by laser-based powder bed fusion of metals (PBF-LB/M) under three representative processing conditions. Microstructural characterization reveals a strong correlation among thermal input, solidification behavior, and microstructural anisotropy. Among the investigated conditions, the combination of high laser power and high scan speed results in reduced porosity, fewer microcracks, and minimized lack-of-fusion defects. Three-dimensional finite element method (FEM) simulations combined with phase-field modeling (PFM) are used to quantify the thermal gradients and cooling rates and to predict dendritic growth behavior. The optimized high-power and high-scan-speed condition produces a relatively low thermal gradient, promoting dendrite impingement. This impingement reduces undercooling and consequently decreases the solute partitioning between the cell core and cell boundary. In addition, the high-laser-power condition induces a relatively low interface velocity and a larger dendrite tip radius, thereby suppressing the segregation of γ′-forming elements through the Gibbs–Thomson effect. As a result, this condition leads to a relatively low volume fraction of MC carbides, which may enhance γ′ precipitation strengthening during post-heat treatment. This study provides new insights into the process–structure–property relationships in PBF-LB/M-processed IN738LC and establishes an integrated modeling framework for predicting microstructure evolution and elemental segregation in Ni-based superalloys.

Inconel 939 (IN939) is a nickel-based superalloy known for its excellent mechanical properties and oxidation resistance at high temperatures, making it suitable for hot-section components in industrial gas turbines. However, when fabricated by additive manufacturing (AM), IN939 is prone to process-induced defects and microcracking, and its creep properties are inferior to those of conventionally cast materials. These limitations have restricted the broader application of AM-fabricated IN939 in gas turbines.This study aims to develop optimized laser powder bed fusion (L-PBF) process parameters to suppress defects and micro-crack formation during fabrication, and to establish heat treatment cycles that enhance creep performance compared to previously reported AM-fabricated IN939. In the basic stage, a stable process window achieving a relative density above 99.9% was identified while meeting room-temperature tensile property targets. Subsequently, heat treatment conditions were systematically investigated to obtain required high-temperature mechanical properties, including tensile strength, low-cycle fatigue, and creep resistance. In the advanced stage, AM process parameters were refined to enable fabrication of complex geometries while improving part quality, particularly surface roughness. Mechanical properties at elevated temperatures were evaluated, and high-temperature behavior was analyzed to clarify correlations between AM process parameters, heat treatment, and mechanical properties.The results demonstrate that the optimized L-PBF parameters and heat treatment cycles satisfy targeted mechanical properties within the investigated range and improve high-temperature performance. This study provides a foundation for AM processing parameters for gas turbine hot-section parts and supports the expansion of AM technologies to other nickel-based superalloys for high-temperature applications.

In this study, a crack-free Al94Fe2.5Cr2.5Ti alloy was successfully fabricated by significantly increasing the scanning speed while moderately enhancing the laser power in laser powder bed fusion (L-PBF) technology. The alloy exhibits exceptional mechanical properties from room temperature to elevated temperatures (up to 500 ◦C). Notably, the alloy demonstrates an optimal combination of ultimate tensile strength (547.17 ± 10.13 MPa) and elongation (7.00 ± 1.12 %) at room temperature, maintaining 271.47 ± 12.08 MPa at 400 ◦C and 111.53 ± 6.71 MPa at 500 ◦C, much higher than the currently reported heat-resistance aluminum alloys. The excellent mechanical behavior of the alloy primarily originates from two synergistic mechanisms: (1) Dispersion strengthening by high-density ultrafine icosahedral quasicrystalline (i-QC) particles (about 20~300 nm) with exceptional thermal stability within the bimodal composite microstructure, and (2) grain boundary strengthening provided by grain refinement. This study reveals that the synergistic "low-power/high-scan-speed" strategy in additive manufacturing effectively promotes grain/phase refinement while facilitating the formation of highdensity nanoscale i-QC dispersoids through nonequilibrium solidification. This approach enhances the mechanical properties of aluminum alloys across wide temperature ranges, establishing a novel paradigm for heatresistant alloy design.

AlSi10Mg alloy is widely used in aerospace and defense industries, and its application has expanded with the adoption of additive manufacturing processes such as selective laser melting (SLM). However, the as-built microstructure formed under rapid cooling consists of fine cellular α-Al grains and non-equilibrium microstructural features, leading to limited mechanical performance due to brittleness and crack susceptibility. In this study, the microstructural evolution and room-temperature tensile properties of SLM-fabricated AlSi10Mg alloy subjected to conventional T6 and annealing heat treatments were investigated, and a new heat-treatment strategy was proposed to mitigate strength degradation while maintaining adequate ductility. The as-built alloy exhibited cellular α-Al grains (5.6–13.8 μm) surrounded by a continuous Si-eutectic network (~380 nm). Under T6 treatment, the Si network collapsed during solution treatment with Si particle coarsening, followed by the precipitation of nanoscale β'' (2–5 nm) during aging. Annealing led to partial network collapse and the formation of intragranular Si nanoparticles (≥20 nm). While both treatments reduced strength compared to the as-built condition, the annealed alloy showed more favorable plastic deformation behavior. The newly designed heat-treatment condition exhibited enhanced tensile strength and Vickers hardness compared to conventional treatments, suggesting an optimized heat-treatment strategy for additively manufactured Al alloys.

Mechanical properties anisotropy and coarse columnar grains commonly form in additively manufactured austenitic stainless steel, particularly in arc additive manufacturing with high heat input. In this study, we demonstrate a strategy to achieve uniform and enhanced mechanical properties in plasma powder arc additive manufacturing. We show that alloying Ni, Al and Ti into the 316L stainless steel enables the introduction of a small amount of δ-ferrite phase, thereby homogenizing and refining the subsequently formed austenite phase. The alloying elements also promote high density precipitation within the δ-ferrite grains and along the grain boundaries. Thus, uniform and strong austenite stainless steel is obtained directly from printing. Aging treatment results in a decrease of precipitate density in δ-ferrite and introduces high density of precipitates in austenite phase, further enhancing the strength almost without a compromise in ductility. This strategy provides a pathway to achieve uniform and strong additively manufactured alloys.

This study investigates the micromechanical behavior of additively manufactured multilayer samples composed of alternating hard CoCrNi and soft CoCrNi₂ medium-entropy alloy (MEA) layers fabricated by laser powder bed fusion (L-PBF). Macro- and micro-scale mechanical testing and digital image correlation (DIC) analysis, together with finite element simulations, reveal coupled global–local deformation behavior and complex strain interactions within individual layers and interfacial regions. In addition, we developed a new quantitative approach that combines nanoindentation experiments and micro-DIC analysis to simultaneously probe local strength and strain distribution. From all above results, we explored the micromechanical role of a compositionally graded zone between the layers and the underlying deformation mechanisms in the examined multi-layered MEA systems.

Fe-12Mn alloy possesses one of the most interesting microstructures: a blocky α′-martensitic structure with twinning relationships and a sub-micrometer grain size. Although these indicate the possibility of a highly desirable grain-refinement effect, this alloy exhibits low yield stress and is inherently brittle; its ductile-to-brittle transition temperature (DBTT) occurs near ambient temperature, leading to poor impact toughness at subzero temperatures. Here, we fabricated a composite-like Fe-12Mn alloy that exhibits an ultrahigh yield strength (~ 1 GPa) and a DBTT of - 50 oC. Such an excellent strength-impact toughness combination is achieved by utilizing the synergistic effect of chemical heterogeneity and metastability engineering concepts, e.g., the transformation-induced plasticity effect from a unique two-step γ→ε→α′ martensitic transformation. The feasibility of this newly designed alloy lies in its sustainability, i.e., containing an impurity amount of carbon yet exhibiting exceptional properties, and its economic potential as an alternative to other high-cost alloys for extreme environments.

Laves phases are important high-temperature structural materials, yet their widespread applications are severely limited by intrinsic room-temperature brittleness. Although considerable efforts have been devoted to understanding their deformation mechanisms and phase stability, the atomic-scale nature of complex crystal defects and their roles in microstructural evolution and fracture remain poorly understood.In this work, a NbCr₂ Laves phase alloy was employed as a model system. We systematically investigated the atomic structures and formation mechanisms of complex defects associated with polymorphic transformation and dislocation interactions.For the C36→C15 polymorphic transformation, the atomic-scale structure of the incoherent phase boundary was resolved. The interface was found to consist of multiple periodically repeated structural motifs rather than a single uniform configuration. Distinct defect features, including Nb antisite columns and Cr vacancy-like columns, were identified at the interface In addition, four types of dislocation lock structures formed through stacking-fault interactions were identified in the C15 phase, including Lomer–Cottrell-type and Hirth-type locks. Atomic-resolution characterization revealed the existence of Nb antisite and Cr vacancy-like columns within the lock cores. . Meanwhile, pronounced stress accumulation was observed around the lock structures, suggesting that they can act as preferential crack initiation sites.These findings establish atomic-scale correlations among complex defect structures, polymorphic transformation behavior, and mechanical response in Laves phases. The present work provides new insights into defect-controlled embrittlement mechanisms in intermetallic compounds and offers guidance for the defect engineering of advanced high-temperature structural materials.

Additive manufacturing (AM) alloys exhibit complex, hierarchical microstructures, typically characterized by bimodal grain size distributions and sub-micron dislocation cellular structures. To elucidate the role of these features in fatigue damage accumulation, this study utilizes in-situ electron channeling contrast imaging (ECCI) to establish a quantitative characterization framework for investigating the cyclic deformation behavior of a CrCoNi alloy. An in-situ characterization and analysis system was developed to track the dislocation substructure evolution within individual grains. This methodology offers multi-scale advantages, effectively balancing high-resolution microscopic characterization with macroscopic statistical significance. Leveraging the high-resolution capabilities of in-situ ECCI allows for the systematic characterization of dislocation substructure features at the sub-micron scale. Simultaneously, the large field-of-view (FOV) capability of the scanning electron microscope (SEM) enables statistical analysis across hundreds of micrometers, allowing for the differentiation of deformation behaviors between various grain populations within the AM-induced bimodal structure. This research focuses on the analysis of dislocation substructure evolution and the deformation of heterostructured grains under cyclic loading, including the formation of persistent slip bands (PSBs) and the evolution of AM-induced dislocation cells. By integrating local crystallographic parameters with real-time microstructural observations, the fatigue damage accumulation process in complex heterostructured material systems can be precisely assessed. These methodological advancements provide a robust data and theoretical foundation for the targeted optimization of fatigue resistance in additively manufactured alloys.

Controlling brittle intermetallic compounds (IMCs) at reactive bimetallic interfaces remains a key challenge in materials design. Here, we use in-situ synchrotron X-ray radiography to reveal an oscillatory redistribution of Sn-rich liquid at the Al–Sn/steel solidification front — a transient phenomenon hidden from post-mortem analysis. Coupled phase-field and Navier–Stokes simulations identify solutocapillary Marangoni convection as the governing mechanism: concentration-dependent surface-tension gradients at the immiscible liquid–liquid interface drive microscale vortices (Pe ≈ 5) that, once activated by sufficient intermetallic growth, disperse the Fe-enriched boundary layer and redistribute solute across the reaction front. While this convection attenuates individual particle growth, it creates Al-rich conditions at new locations that promote widespread nucleation of the tougher θ-Fe₄Al₁₃ phase over the brittle η-Fe₂Al₅ phase. Our findings demonstrate that the strategic introduction of an immiscible, surface-active liquid phase can tune interfacial reaction kinetics, offering a design principle for tailoring microstructural evolution in immiscible alloy systems and multi-material joints.

Scanning Electron Microscopy (SEM) is widely used for quantitative microstructural analysis of metals and alloys. However, SEM-based image analysis can be influenced by several imaging and processing factors, such as focus and defocus conditions, image noise, local contrast variation, and threshold sensitivity. These factors may introduce uncertainty in the quantitative evaluation of precipitate fraction, precipitate size, and inter-precipitate distance.In this study, Atomic Force Microscopy (AFM) was applied as a complementary approach to evaluate the reliability of SEM-based precipitate quantification. The same region of the same specimen was analyzed using both SEM and AFM, and the measured precipitate characteristics were compared in terms of fraction, size, and spatial distribution. Because AFM provides surface topography and height information, it can help distinguish precipitates more clearly in regions where SEM images show low contrast or local imaging variation.The comparative SEM–AFM analysis suggests that AFM-based topographical data can support more reliable precipitate identification and reduce uncertainty in SEM-based quantitative analysis. This approach provides a useful strategy for improving the reliability of precipitate characterization in microstructure-based materials evaluation.

Deformation twinning offers a versatile route to such architectures, partitioning a single-phase matrix into twinned and untwinned domains whose orientations, and thus properties, diverge sharply. In this study, pre-twinned AZ31 is treated as a model twin–matrix heterostructure to examine how its internal heterogeneity steers the coupled electrical, thermal, and microstructural response under electropulsing. Rolling-direction pre-compression converted about 75% of the volume into reoriented extension-twin domains. Electropulses were then applied along two orthogonal directions, with durations tuned to equalize peak temperature and isolate non-thermal contributions. As the twin and matrix domains present different crystallographic axes to the current, the heterostructure displays a direction-dependent effective resistivity that a simple rule-of-mixtures reproduces quantitatively. Quasi-in-situ electron backscatter diffraction tracked identical regions across successive pulses. Early evolution proceeded by strain-induced boundary migration, with nucleation and growth emerging only in later cycles, while thermally activated twin-boundary motion stayed suppressed under sub-second heating. Contradicting expectations from texture and grain morphology, one pulsing direction markedly accelerated boundary migration and twin annihilation. This is attributed to current crowding within low-resistivity twin domains, which locally intensifies the athermal driving force—an interaction intrinsic to the heterostructure. The accelerated, heterogeneity-driven evolution delayed plastic instability and achieved a 71% ductility recovery for that pulsing geometry, compared to 19% for the orthogonal case. These results position deformation twins as designable heterostructures that turn multi-physics coupling into mechanical benefit.

Generally, nanosized materials benefit from high strength, but suffer from low plasticity. Heterostructures including laminate show a great potential of achieving high strength and high plasticity simultaneously. In this study, the metallic laminated composites were selected as models to reveal the interface dominated high strength and high plasticity.Laminated composites were prepared by two methods, accumulative roll bonding (ARB) and physical vapor deposition (PVD). Firstly, a multilayer Cu-Nb composite sheet consisted of 10 nm monolayers was prepared by ARB. High-resolution transmission electron microscopy characterization showed that after large plastic deformation, most of the Cu-Nb interface become stable with a definite orientation relationship and ordered atomic structure. This structure determines that this kind of nano-laminated metal composites have high strength, high thermal stability, and excellent radiation resistance. Secondly, in order to expand the understanding of interface effects in laminated materials, we have also modified the atomic interface structure of nano-laminated materials, and revealed the regulation mechanism of interface amorphous on the enhancement of the strength and plasticity. Finally, to reduce the effect of the strong anisotropy and insufficient plasticity of laminated metals and alloys, we have proposed a route that introducing three-dimensional interfaces to improve the strength and plasticity simultaneously.

The Liquid Metal Dealloying (LMD) process selectively removes desired alloying elements from a precursor alloy in the metallic melt. Concurrently, 3D interconnected ligament structure was remained within the precursor alloy. In this study, a CoCrFeMnNi high-entropy alloy (HEA) precursor was examined in pure Cu and Cu–Ag melts, revealing distinct differences in dealloying, phase evolution, and properties. Among the five constituent elements of the HEA precursor, Mn and Ni preferentially dissolved in the Cu melt, and interconnected Cu-rich melt channels were formed in the precursor. Simultaneously, Cu diffused into the CoCrFe-rich solid ligaments. The heterostructured material comprised dual face-centered cubic (fcc) phases with refined grain sizes and high interconnectivity. Increases of 7 % and 82 % were observed in the hardness and electrical conductivity of the dual fcc heterostructured HEA, and these improvements are attributed to the HEA's unique 3D interconnected microstructure. In Cu–Ag melts, Ag addition suppressed the dissolution of precursor elements, except for Mn, owing to their low solubility and immiscibility in Ag. Notably, the heterostructure material processed in Cu-Ag melt exhibited a slight decrease in hardness (∼4.7 %) while achieving a 3.2-fold increase in electrical conductivity compared to the precursor. This work demonstrates that tailoring melt composition suppresses excessive precursor dissolution. It further enables the design of 3D interconnected heterostructured HEA composites with controlled architectures.

This study investigated the oxidation behavior of Nb-controlled AlVCrZr system refractory high-entropy alloys (RHEAs), with particular emphasize on the role of heterophase microstructures. Owing to the large melting-point differences among the constituent elements, the alloys were processed powder metallurgy consisting of mechanical alloying, spark plasma sintering, and heat treatment. The Nb content altered distribution of element-rich phases and phase boundary within the alloys, which directly affected oxygen penetration pathways and oxide formation. Isothermal oxidation tests revealed that the oxidation rate, scale continuity, cracking behavior, and internal oxidation response changed markedly depending on the Nb content. In the low-Nb content alloys, phase separation and selective oxidation associated with specific enriched constituent phases were observed. With increasing Nb content, the oxidation behavior shifted toward diffusion-dependent behavior accompanied by cracking. As a result, the high-Nb alloys exhibited poor oxidation resistance. Atomic scale analysis clearly showed oxygen penetration beneath the oxide scale along grain boundaries and phase boundaries. These findings highlight the significance of heterophase microstructures as a critical design factor for controlling interfacial oxygen transport, internal oxidation, and oxide stability in RHEAs.

Magnetic refrigeration based on the magnetocaloric effect (MCE) is attracting increasing attention as an environmentally friendly alternative to conventional vapor-compression cooling technologies. The performance of active magnetic regeneration (AMR) systems depends not only on the intrinsic properties of magnetocaloric materials but also on the design of magnetocaloric beds operating over a broad temperature range. Since the MCE reaches its maximum near the magnetic transition temperature (Tc), AMR beds typically require multiple materials with different Tc values. Such multilayered or compositionally graded assemblies can be regarded as functional heterostructures. Among room-temperature magnetocaloric materials, La(Fe,Si)13-based alloys are promising candidates due to their large MCE associated with itinerant-electron metamagnetism (IEM). Their Tc can be effectively tuned through hydrogenation and Mn substitution, making La–Fe–Mn–Si alloys suitable for constructing Tc-graded magnetocaloric regenerator beds. In this study, Mn-controlled La–Fe–Mn–Si alloys are investigated to tailor Tc and optimize processing conditions for the formation of the NaZn13-type 1:13 phase. For practical AMR operation, surface and interface stability must also be considered because repeated exposure to heat-transfer fluids may induce corrosion, oxidation, particle degradation, and thermal-contact issues. Therefore, magnetocaloric beds should be designed not only as compositionally graded structures but also as coating-integrated functional heterostructures that balance magnetocaloric performance, durability, corrosion resistance, and thermal transport. This presentation discusses materials design and processing strategies for developing La–Fe–Mn–Si-based functional heterostructures for AMR applications, with emphasis on Tc tuning, 1:13 phase formation, graded-bed design, and surface/interface engineering.

Gradient-structured materials have emerged as a promising approach to overcoming the long-standing strength-ductility trade-off in metallic materials. However, most previous studies have mainly focused on their behavior under quasi-static loading, and their mechanical response under high-strain-rate conditions remains insufficiently understood. In this work, the fabrication of gradient structures and their dynamic mechanical behavior were systematically investigated in order to identify the key material attributes required for gradient-structure formation and to clarify the deformation mechanisms of heterogeneous regions under dynamic loading. Gradient structures were first introduced into low-carbon steel and TWIP steel by cyclic torsion. The results show that the gradient effect and mechanical performance of low-carbon steel are significantly weaker than those of TWIP steel. This difference is primarily related to the extensive activation of deformation twinning in TWIP steel, which provides favorable pathways for dislocation glide and promotes dislocation pile-up at twin boundaries, thereby generating a dynamic Hall-Petch effect that enhances strain hardening while preserving ductility. These findings demonstrate that strong strain-hardening capability is a crucial prerequisite for effective gradient-structure fabrication. Furthermore, a high-entropy alloy with high strain-hardening capacity was selected to construct a gradient structure, and its compressive behavior was studied over strain rates from 10-4 to 3×103 s-1, revealing pronounced positive strain-rate sensitivity and clear regional deformation heterogeneity. This study provides a theoretical basis for the design and fabrication of gradient-structured materials and for the regulation of their dynamic service performance.

Al-based coated hot-press-forming (HPF) steels comprise a coating/steel heterostructure consisting of brittle intermetallic layers and a ferritic interlayer on a martensitic substrate. Under hydrogen (H) conditions, cracks can initiate in the brittle coating and propagate into the substrate. In prior studies, coating microstructure and diffusible H content often varied simultaneously among specimens. This made it difficult to distinguish the effect of the coating microstructure from that of H content on crack initiation and propagation. Here, we decouple these effects by controlling the dew point during austenitization to tune H absorption and by comparing Al–Si- and Al–Fe-coated 31MnB5 steels under both identical dew point and comparable diffusible H content. Interrupted slow strain rate tensile tests combined with cross-sectional SEM-EBSD tracked strain localization and crack-path evolution. In the Al–Si-coated steel, vertical cracks formed in the intermetallic layer were arrested at an interfacial Kirkendall void band and preferentially deflected along the interface, while localized deformation developed in the underlying ferritic interlayer. At higher strain, this localized deformation in the ferritic interlayer was associated with subsequent cracking into the substrate. In contrast, in the Al–Fe-coated steel where the Kirkendall void band was absent, vertical cracks were more readily penetrated through the ferritic interlayer into the substrate, leading to more extensive brittle cracking despite comparable diffusible H content. These results highlight that crack-path transition in coated HPF steels is governed not only by diffusible H content but also by heterostructure-specific interfacial defects and the deformation response of the ferritic interlayer.

Heterostructured metals derive their exceptional strength and damage tolerance from internal interfaces, yet their dynamic stability under extreme surface loading remains poorly understood. Here we report the scale-dependent frictional and wear response of electrodeposited nanotwinned Ni with controlled twin lamella spacing, providing a mechanistic framework for how nanotwinned architectures accommodate severe tribological deformation. Under nanoscale contact, the coefficient of friction exhibits a non-monotonic dependence on twin spacing, governed by a transition from dislocation–twin-boundary interactions to detwinning-mediated interfacial softening. Under microscale scratching, both friction and wear decrease systematically with decreasing twin spacing. This improvement arises from an unexpected friction-induced FCC-to-HCP phase transformation in the near-surface layer, enabled by ultrafine nanotwins that reduce the energetic barrier for stacking-sequence rearrangement. In contrast, under macroscale reciprocating sliding, friction becomes nearly insensitive to twin spacing, while wear resistance is optimized at relatively larger twin spacings. This regime is controlled by the formation of a durable nanocrystalline oxide film and a stable gradient nanostructured subsurface layer, which together suppress cracking, delamination, and catastrophic material removal. These results reveal that heterostructured materials do not obey a universal strengthening–wear relationship under dynamic contact. Instead, their performance is dictated by the interplay among interface-mediated plasticity, phase transformation, oxidation, and gradient structural evolution across loading scales. The work establishes nanotwin spacing as a critical architectural parameter for designing metallic surfaces capable of maintaining low friction, high wear resistance, and structural stability in demanding aerospace, nuclear, and defense environments.

 Ni-based FCC alloys are promising cryogenic structural materials due to their ductility retention and plastic deformation stability at low temperatures. However, the Ni-C alloy in this study exhibited anomalous behavior inconsistent with conventional Hall–Petch and ductile-brittle transition theories, including strength enhancement with increasing grain size and improved ductility at cryogenic temperatures, motivating a deeper investigation into the underlying deformation mechanisms.Ni-C alloys were fabricated by induction melting and casting, cold-rolled to 85% thickness reduction, and heat-treated at 650°C, 850°C, and 1000°C for 4 hours with water quenching, yielding fully recrystallized microstructures. Tensile tests were conducted at 298 K and 77 K at a strain rate of 1×10⁻³ s⁻¹, and local deformation behavior was characterized using DIC, EBSD, and nanoindentation.Despite grain coarsening, strength and elongation improved simultaneously at room temperature, and serration was observed in specimens heat-treated at higher temperatures. At 77 K, all specimens exhibited higher strength and ductility compared to room temperature, with distinct fracture characteristics confirmed by fractographic analysis. These results indicate that carbon behavior, local deformation stability, and fracture characteristics collectively govern the mechanical response of Ni-C alloys beyond grain size effects.

Fusion energy offers a clean and sustainable power source capable of mitigating global warming. ITER, the largest international fusion program, aims to demonstrate the scientific feasibility of nuclear fusion. In DEMO reactors, structural materials will occupy the majority of the in-vessel regions, and several blanket concepts will be tested. Reduced activation ferritic/martensitic (RAFM) steels, based on 9Cr alloys, are considered key candidates due to their excellent resistance to swelling, favorable thermal properties, and low activation characteristics.However, fusion environments contain significant amounts of deuterium and tritium, which diffuse into plasma-facing and structural components. Neutron irradiation generates defects that trap hydrogen isotopes, increasing susceptibility to hydrogen-induced degradation. High operating temperatures further accelerate hydrogen diffusion and trapping, potentially leading to degradation of structural integrity.In this study, creep tests at 550 °C were performed under Ar and H2 atmospheres to evaluate hydrogen effects. Hydrogen exposure drastically reduced creep life and increased steady-state creep rates, while the total creep strain remained unchanged. These results suggest enhanced dislocation mobility and accelerated recovery. Microstructural observations—including lath boundary evolution, dislocation structures, and carbide stability—were used to clarify hydrogen’s role in high-temperature creep mechanisms under fusion-relevant conditions.

Thermal barrier coatings (TBCs) are intrinsically heterostructured materials, integrating a superalloy substrate, a metallic bond coat, a thermally grown oxide (TGO), and a ceramic top coat into a single multilayered architecture whose performance is governed by the stability of its buried hetero-interfaces. As gas-turbine inlet temperatures continue to rise, conventional MCrAlY bond coats and yttria-stabilized zirconia (YSZ) top coats approach their limits, motivating new design strategies. Here we demonstrate that high-entropy materials provide a powerful route to engineer each layer and its interfaces simultaneously. On the metallic side, NiCoCrAlY bond coats were compositionally complexified with Nb, Ti, Mo, and Ta and oxidized at 1000 °C for up to 500 h. Niobium-bearing high-entropy alloys formed a dense, uniform TGO with markedly improved bond-coat/TGO interfacial stability and suppressed oxide growth, and cross-sectional analysis confirmed the thinnest TGO layers for Ti- and Nb-containing compositions. On the ceramic side, single-phase high-entropy oxides were synthesized through three strategies—maximizing atomic-mass mismatch, incorporating divalent cations to generate oxygen vacancies, and a TGO-driven spinel design—yielding defective-fluorite and spinel structures with thermal conductivities as low as 1.27 W/m·K, roughly 50% below YSZ, while retaining comparable thermal expansion and mechanical properties. A poorly sinterable high-entropy silicate further showed promising CMAS resistance for environmental barrier coatings. Collectively, these proof-of-concept results show that entropy stabilization enables tailored, defect-rich heterostructures and robust hetero-interfaces across the entire coating stack, offering a unified materials platform for higher-temperature, longer-lived gas-turbine TBCs deposited by plasma-spray processes well suited to entropy stabilization.

Three-dimensional lattice structures have been actively studied because they enable the tailoring of mechanical and thermal properties through geometric design. In this study, the effects of lattice volume fraction on the microstructure and thermal transport properties of 316L stainless steel–copper composites were investigated to improve their thermal properties. To achieve this, three types of octet-truss structures with different volume fractions were fabricated using Selective Laser Melting (SLM), and copper-filled composites were subsequently produced using Spark Plasma Sintering (SPS). During the SPS process, different local current density distributions were formed within the composites depending on the lattice volume fraction, resulting in variations in interfacial diffusion behavior and microstructural evolution. As a result, current density variations induced by the lattice volume fraction affected the interfacial microstructure and elemental diffusion behavior, leading to changes in thermal contact conductance and effective thermal conductivity. This study suggests that lattice structure design can be utilized to control current density during SPS processing and thereby improve the thermal performance of metal composites.

This study aimed to improve the poor cryogenic ductility and high susceptibility to hydrogen embrittlement of as-deposited SAF 3207 hyper-duplex stainless steel through a laminated composite design. A multi-material directed energy deposition additive manufacturing strategy was used to fabricate a SAF 3207/AISI 316L laminated composite with a heterogeneous architecture of alternating austenitic and austenitic–ferritic duplex layers. The laminated structure promoted strong hetero-deformation-induced back-stress hardening, in-situ twin formation, and strain-induced martensitic transformation. The architected microstructure significantly enhanced tensile behavior at cryogenic temperatures compared with that of monolithic SAF 3207. Under hydrogen-charging conditions, the laminated composite retained high strength and ductility with limited susceptibility to embrittlement, whereas monolithic SAF 3207 suffered severe hydrogen-assisted cracking. These findings provide new insights into the additive manufacturing of heterostructured materials for extreme-environment applications.

The development of heat-resistant aluminum alloys for additive manufacturing has long been constrained by near-eutectic compositions to avoid solidification cracking, while conventional eutectic designs typically suffer from insufficient strength. Here we introduce a printable hypereutectic Al–Ce–Mg–Sc–Zr alloy enabled by laser powder bed fusion. Unlike conventional LPBF near-eutectic aluminum alloys that generally form discontinuous worm-like eutectic structures, the present alloy develops a unique three-dimensional continuous cellular heterostructures throughout the as-printed microstructure. This cellular architecture delivers an outstanding tensile strength of ~330 MPa at 300 °C, which is 3–5 times higher than conventional aluminum alloys and surpasses state-of-the-art eutectic Al–Ce and Al–La systems. Remarkably, after ultra-long-term thermal exposure at 350 °C for 2000 h, the initial cellular heterostructures completely transform into a high-density dispersion of ultrafine Al₁₁Ce₃ nanospheres, with L12-Al₃(Sc,Zr) nanoprecipitates segregated at the interface of α-Al/Al₁₁Ce₃. This hierarchical heterogeneous microstructure effectively suppresses coarsening and maintains a short dislocation length scale, resulting in a retained room-temperature strength of ~400 MPa. These findings highlight the potential of architected heterogeneous microstructures enabled by additive manufacturing for the development of next-generation heat-resistant aluminum alloys operating under extreme thermal conditions.

High-strength 7075 aluminum alloy is attractive for lightweight structural applications owing to its excellent precipitation-hardening capability. However, its application in directed energy deposition (DED) remains limited by solidification cracking, Zn/Mg volatilization, and severe solute segregation during rapid solidification. In particular, Cu-, Zn-, and Mg-enriched residual liquid films can form along interdendritic or grain-boundary regions, promoting crack formation and reducing the effective solute content available for subsequent precipitation strengthening. In addition, conventional Zn–Mg–Cu precipitates may coarsen during elevated-temperature exposure, resulting in limited high-temperature stability.In this study, reaction-phase-forming ceramic particles are explored as potential modifiers for improving the printability and elevated-temperature stability of DED 7075 aluminum alloy. CeO₂ and BN are selected as representative oxide- and nitride/boride-based particles, respectively. CeO₂ may partially react with molten aluminum to form thermally stable Al₂O₃ and Al–Ce intermetallic phases, while BN may form AlN or AlB₂-type phases during laser processing. These reaction products are expected to act as heterogeneous nucleation sites or high-temperature stable dispersoids, potentially refining the solidification structure and disrupting continuous solute-rich liquid films.Powder processability and particle dispersion are first examined, followed by single-track and bulk deposition trials. Crack formation, melt-pool morphology, Cu-rich segregation, phase formation, heat-treatment response, and hardness retention after elevated-temperature exposure are then evaluated. This study aims to clarify the feasibility of using reaction-phase-forming ceramic particles to mitigate cracking, solute segregation, and high-temperature property degradation in DED 7075 aluminum alloy.

High-γ′ Ni-based superalloys exhibit limited printability during additive manufacturing (AM) due to steep thermal gradients that promote cracking. Most conventional alloys exhibit a negative γ/γ′ lattice misfit, where the superposition of residual stresses and precipitation-induced stresses drives strain-aging cracking (SAC). A positive (=reverse) γ/γ′ lattice misfit was introduced as an alloy-design strategy to induce compressive residual stresses in the γ matrix, thereby mitigating precipitation-induced cracking. To enhance AM reliability while preserving γ′ strengthening, a modified IN738LC-based composition with a tailored positive misfit was developed for L-PBF. The developed alloy achieved near crack-free fabrication and retained a bimodal γ′ microstructure comparable to IN738LC. HRXRD at room temperature revealed a lattice misfit of δ=+0.31% in the developed alloy (CWAM), significantly higher than in IN738LC (δ=+0.02%). In-situ HRXRD confirmed that the positive misfit persisted up to 700℃ without significant change from the RT value. Beyond 700℃, the misfit progressively decreased but remained above +0.15% even at 800–900℃. To assess SAC resistance, direct aging was applied under four different thermal conditions (850℃ and 1100℃ with water quenching) to as-built V-notch specimens. After aging at 1100℃ for 1 hr, GND density increased in IN738LC but decreased in CWAM despite comparable precipitation behavior. The maximum crack density decreased from 2.87% in IN738LC to 0.14% in CWAM, demonstrating the effectiveness of misfit-driven residual stress control as an alloy-design strategy for additive manufacturing.