The mechanisms underlying property degradation in heat-affected recycled powders during directed energy deposition (DED), and their effects on the microstructure and mechanical properties of the final builds, have not been systematically investigated. This knowledge gap hinders sustainable and economically viable feedstock recycling. This study presents a new build-area optimization strategy and quantifies the proportion of heat-affected particles within recycled powder collected from prior DED builds. Furthermore, the influence of recycling-induced oxide inclusions on the microstructural evolution, mechanical properties, and tribological behavior of DED-built 316L stainless steel (SS) is systematically investigated and benchmarked against original powder builds. DED-built 316L SS fabricated from recycled powders exhibited pronounced microstructural degradation, including higher porosity, similar to 32% greater surface roughness, similar to 4.2 & times; larger oxides, similar to 3.6 & times; higher oxide fraction, and similar to 65% coarser grains. Despite these changes, hardness increased with only a marginal influence on compressive strength, whereas ductility decreased by similar to 45% due to oxide inclusions, as confirmed by experiments and finite-element simulations. Fractography revealed crack initiation at oxide-matrix interfaces or within oxides, accelerating crack propagation and producing a more brittle fracture response. TEM confirmed oxide coarsening, dislocation pinning, and microstructural instability as the primary mechanisms impairing plastic deformation in recycled-powder builds. Tribological characterization showed reduced wear rates at early times (reductions of 3.49% at 1 min and 11.36% at 20 min), attributable to work hardening and protective tribo-oxide layers; over longer durations, overall wear resistance remained comparable across conditions. These findings elucidate the link between powder recycling, oxide evolution, and property trade-offs, advancing sustainable feedstock-recycling strategies in metal additive manufacturing.

A core-shell microstructure represents an approach to achieve superior mechanical properties in alloys through its distinctive architecture, typically developed in powder metallurgy processing. In the present study, an integral core-shell structure has achieved in a cast Ni-based high entropy alloy through a straightforward thermo-mechanical processing (TMP) approach, including hot rolling and heat treatment. Inspired by the formation of a necklace structure during the hot deformation, we employed hot rolling to induce bulged grain boundaries in coarse grains. Subsequent heat treatment constrained the growth of these bulged regions through B2 precipitate formation, leading to the stabilization of the integral core-shell structure, where the deformed grains form the core, and the bulged grains form the shell. The significant synergistic hardening from the microstructural heterogeneity of the integral core-shell structure improves strain hardening in the TMP-processed sample. The integrated TMP approach, combined with alloy design, enables the evolution of integral core-shell structures in cast high entropy alloys, significantly improving material properties without the complexities of powder metallurgy. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Recycling non-deposited powders generated during directed energy deposition (DED) is essential for improving the sustainability of metal additive manufacturing, yet the effects of powder collection distance on recyclability remain unexplored. This study investigates the microstructural evolution and oxidation behaviour of 316L stainless steel (SS) powders collected at 10, 15 and 32 cm from the DED melt pool, and quantitatively evaluates their reusability as a function of both collection distance and particle size. Ex situ heat treatments of virgin powders at 650-1000 degrees C were also performed to clarify oxidation pathways and correlate thermally induced oxide formation with that observed in recycled powders. By combining detailed microstructural characterization and phase analysis, this work identifies the distinct oxidation mechanisms active during DED processing and thermal exposure. Within the 50-150 mu m size range, non-deposited powders were classified as heat-affected powders (HAPs) or reusable powders based on their surface characteristics. HAPs collected at 32 cm exhibited significantly coarser surface pores, approximately 61 % and 17 % larger than those collected at 10 and 15 cm, respectively. Recycled powders were enriched in Cr/Fe-rich oxides, consistent with the oxidation behaviour of heat-treated virgin powders. Powder recyclability decreased with increasing collection distance, yielding reuse rates of 86 %, 75 % and 69 % at 10, 15 and 32 cm, respectively, whereas particles smaller than 100 mu m retained comparatively higher reuse potential even at longer distances. These findings establish how collection distance and particle size control powder recyclability and provide a basis for distance and size-selective recovery strategies for sustainable DED powder recycling.

This study investigates the microstructural evolution, cryogenic deformation behavior, and residual stress of butt laser-welded Co17.5Cr12.5Fe55Ni10Mo5 complex concentrated alloy (CCA). Two laser welding parameter sets-15 mm/s at 0.6 kW and 20 mm/s at 0.7 kW-were optimized through preliminary bead-on-plate experiments, achieving full penetration without macroscopic geometric defects, and yielding pore volume percentages of 0.0092% and 0.0677%, respectively, as quantified by X-CT. Both welding conditions resulted in columnar grains in the fusion zone (FZ), exhibiting a pronounced <001> crystallographic texture oriented perpendicular to the welding direction, accompanied by cellular substructures. Quantitative analysis revealed that the 15 mm/s at 0.6 kW condition produced a higher mu-phase area percentage of 7.0% together with finer cellular features, which correlated with higher hardness values of approximately 200-250 HV in the FZ. Additionally, this condition resulted in a similar to 7.3-fold lower total pore volume compared to the 20 mm/s at 0.7 kW condition, as confirmed by micro-computed tomography. Tensile testing revealed reduced joint efficiency relative to the base alloy, with yield strength, ultimate tensile strength, and total elongation efficiencies of 81.1-86.0%, 74.3-92.3%, and 29.6-70.6%, respectively, primarily due to the presence of micropores, coarse grain formation, and suppressed deformation-induced martensitic transformation (DIMT). Moreover, residual stress analysis showed transverse tensile stresses exceeding 200 MPa near the weld center. Nevertheless, the 15 mm/s at 0.6 kW condition demonstrated reasonable cryogenic mechanical performance, attributed to more active DIMT.

In this study, we explored the influence of laser surface treatment on the microstructural evolution and mechanical properties of a Co17.5Cr12.5Fe55Ni10Mo5 medium-entropy alloy. After laser scanning on the cold-rolled alloy, a heterogeneous microstructure with Mo-rich mu-precipitates formed along the depth from the surface. Notably, laser processing parameters, including scanning speed and the number of scans, affected the macroscopic heterogeneity in the microstructure of the alloy, such as the thickness of the columnar, recrystallized, partially-recrystallized, and non-recrystallized layers. Furthermore, the microstructural features of the lasertreated alloys with a heterogeneous distribution of grains, cellular structures, and precipitates, contributed to the mechanical response of the alloys. As the heat input from the laser heat source increases, the grain coarsening and the absence of non-recrystallized layer have a greater impact on the strength of the laser-treated alloys, even if the precipitates distributed deeper from the surface. These microstructural modifications through laser surface treatment are linked to variations in the mechanical performance of the alloys, indicating that it can be an effective method to tailor the mechanical properties of structural materials.

This study investigates the microstructure and mechanical properties of the Al0.5CoCrFeMnNi high-entropy alloy (HEA), Fe60Co15Ni15Cr10 medium-entropy alloy (MEA) and multicomponent alloys with varying HEA/MEA ratios. These alloys were fabricated using a novel approach that combines gas atomization, low-energy ball milling (LBM) and spark plasma sintering (SPS). The primary objective is to optimize the ratio of hard to soft domains by integrating two effective strategies: introducing microstructural heterogeneity and employing an advanced powder metallurgy processing route. Scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) identified Fe-Ni-rich and Cr-rich regions in the sintered specimens, corresponding to Fe60Co15Ni15Cr10 and Al0.5CoCrFeMnNi grains, respectively. The dual-phase HEA, consisting of face-centered cubic (FCC) and body-centered cubic (BCC) phases, exhibited superior mechanical properties. The multicomponent alloy, composed of 70 wt% HEA and 30 wt% MEA, exhibited better mechanical properties than the MEA due to its heterogeneous trimodal microstructure and phase segregation induced by oxidation. The presence of oxide particles at the HEA/MEA interface acted as dislocation barriers, significantly enhancing the hardness and compressive strength of the multicomponent alloys. This study provides valuable insights into the synergistic strengthening mechanisms arising from the interaction of distinct alloy compositions, offering a promising approach for designing advanced structural materials with tailored mechanical properties.

This study demonstrated the potential for customizing the desired properties of the Co18.5Cr12Fe55Ni9Mo3.5C2 (at.%) ferrous medium-entropy alloy by manipulating the deformation-induced martensite transformation (DIMT) behavior at liquid nitrogen temperature. This was achieved by modifying various initial microstructures through annealing at temperatures ranging from 900 to 1200 °C. The variations in DIMT kinetics were analyzed based on two main factors. (1) Inducing carbide precipitation by annealing at 900 and 1000 °C results in changes in the composition within the matrix, which may affect the stability of the face-centered cubic phase. Samples with a higher volume fraction of the carbide precipitates exhibit lower ΔGFCC→BCC and faster DIMT kinetics. (2) The onset and kinetics of DIMT are also affected by the use of martensite nucleation sites, which may vary depending on the presence of non-recrystallized regions or the grain size. In fine-grained structures, martensite primarily nucleated in the non-recrystallized regions and grain boundaries. However, in coarse-grained microstructures, martensite mainly nucleated along the in-grain shear bands and their intersections. This precise control of the microstructure results in superior properties. The samples annealed at 900 and 1000 °C with carbide precipitates and fine grains exhibit ultrahigh ultimate tensile strength, which may reach elevated values up to ∼1.8 GPa, while those annealed at 1100 and 1200 °C with larger grains and no precipitates exhibit a uniform elongation that exceeds 100%.

In this study, the influence of post-processing heat treatment on microstructure and mechanical properties of Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy fabricated by laser powder bed fusion (L-PBF) was investigated. The mechanical properties of the as-built and heat-treated samples with various temperatures (600–850 °C) were evaluated using a tensile test at room temperature. After heat treatments, both yield strength (YS) and ultimate tensile strength (UTS) gradually decreased, while the tensile elongation tended to increase as the heat treatment temperature increased. These variations were closely related to the microstructural evolution caused by heat treatment. Specifically, the decomposition of α′ martensite into the α + β lamellar structure and subsequent coarsening were promoted with increasing temperature, leading to stress relief and improved dislocation storage capability, which resulted in the variation in mechanical properties. Notably, although the mechanical strength was reduced after heat treatment with increasing temperatures, the lowest yield strength and ultimate tensile strength were measured as 1086.4 ± 16.5 and 1135.0 ± 15.0 MPa, respectively, which are comparable to or higher than those of conventionally processed Ti-6242. As a result, the post-processing heat treatment could be an effective approach to achieve desirable performance for targeted applications.

In this work, the influence of different MXene weight percentages (0, 2, 4, 6 & 10 wt%) on the microstructure, wear behavior, and mechanical properties of CrMnFeCoNi High Entropy Alloy (HEA) were investigated. The CrMnFeCoNi HEA powder and Ti3C2Tx MXene phase were prepared by the gas atomization process and selective etching of the aluminum layer of MAX phase (Ti3AlC2), respectively. Bulk samples of CrMnFeCoNi HEA and HEA matrix-MXene composites were prepared by spark plasma sintering (SPS) using a mixture of CrMnFeCoNi HEA powder that contained 2 wt%, 4 wt%, 6 wt%, 10 wt% of MXene phase. The microstructure evolution, phase structure, and compressive mechanical properties of the samples were investigated at room temperature. It was observed that the CrMnFeCoNi HEA forms a single-phase FCC structure after the gas atomization and SPS process, while the microstructure of the HEA-MXene composites consisted of FCC and HCP phases. The fractions of the MXene phase played important roles in the nanostructural evolution and grain refinement of the HEAMXene composites. The results of mechanical tests indicated that the micro-hardness of CrMnFeCoNi increased from 205.8 HV to 617.6 HV and the yield strength increased from 390 MPa to 1403 MPa with the addition of 10 wt% MXene phase. Moreover, the addition of MXene led to a significant increase in wear resistance and a decrease in the coefficient of friction. The attractive mechanical properties of the HEA-MXene composites were attributed to the grain refinement effect induced by the MXene phase.

Liquid metal dealloying (LMD) is a selective extraction method wherein miscible elements are removed from a precursor alloy to obtain a three-dimensional (3D) interconnected structure. This study presents a novel application of this method to fabricate heterostructured materials from a CoCrFeMnNi high-entropy alloy (CoCr-FeMnNi HEA) precursor immersed in molten Cu at 1095 degrees C, and it elucidates complex dealloying and mutual alloying processes. Of 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 resulting heterostructured material, formed under local equilibrium conditions, comprised dual face-centered cubic (fcc) phases that were characterized by refined grain sizes and high interconnectivity. The transformation from precursor fcc grains to CoCrFe-rich fcc ligaments followed uncommon orientation relationships based on non-close-packed planes. Increases of 7 % and 82 % were observed in the hardness and electrical conductivity of the dual fcc heterostructured HEA, respectively, and they are attributed to the HEA's unique 3D interconnected microstructure. Density functional theory calculations indicated that effective multicomponent mixing contributed significantly to the observed electrical performance, which was superior to that of Cu-containing medium-entropy alloys with conventional microstructures. A key structural factor was the continuous Cu-rich fcc phase, which formed an extensive 3D conductive network to provide exceptional conductivity through the synergistic "cocktail effect." These results highlight the potential of LMD to help achieve multifunctionality in HEA systems via the formation of heterogeneous microstructures.

Crack-free nanocellular graphenes are attractive materials with extraordinary mechanical and electrochemical properties, but their homogeneous synthesis on the centimeter scale is challenging. Here, a strong nanocellular graphene film achieved by the self-organization of carbon atoms using liquid metal dealloying and employing a defect-free amorphous precursor is reported. This study demonstrates that a Bi melt strongly catalyzes the self-structuring of graphene layers at low processing temperatures. The robust nanoarchitectured graphene displays a high-genus seamless framework and exhibits remarkable tensile strength (34.8 MPa) and high electrical conductivity (1.6 × 104 S m-1). This unique material has excellent potential for flexible and high-rate sodium-ion battery applications.

Gradient structure can achieve excellent mechanical properties in metallic materials through synergistic effects from heterogeneity. Conventional surface heterostructuring typically develops one single coupling gradient (i.e., hard surface and soft core). In this study, we present a novel approach to attain a dual-gradient structure, characterized by a series of hard surface-soft middle-hard core, through simple laser-scanning on cold-rolled metastable metallic materials. The resultant dual-gradient structure with significant synergistic strengthening improves the yield strength by more than two-fold compared to its annealed counterparts. Notably, the significant improvement in yield strength does not sacrifice ductility due to the unique deformation behavior of the dynamic-spreading phase transformation. The designed dual-gradient structure induces spatial-distinct phase stability along the depth, enabling to spreading phase transformation from the surface to the center during deformation. The inward-propagating phase transformation contributes to sustaining the heterostructure and the transformation-induced plasticity effect over a wide stress range while detouring stress concentration. Our study suggests a promising process design for fabricating a dual-gradient structure that possesses inward-spreading phase transformation to enhance the mechanical properties of heterostructured materials without compromising their ductility.

Metal additive manufacturing (AM), offering high freedom of design, has garnered attention as a cutting-edge manufacturing technology. Commonly, hot isostatic pressing (HIP), as post-processing, is utilized to remove undesirable defects in AM parts to obtain fully dense components. However, excessive heating during HIP can result in the deterioration of mechanical properties, limiting their potential for structural industry applications. Herein, we propose a new strategy to obtain an optimized gradient structure to achieve a substantial synergistic effect through ultrasonic nanocrystal surface modification (UNSM) on the HIP-processed AM substrate. The resulting microstructure shows an extended gradient layer reaching the center of the substrate with significant mechanical incompatibility between adjacent domains, showing an excellent combination of strength and ductility. Our study suggests that the optimized gradient structure with superior mechanical properties can be achieved by strategically exploiting HIP-induced effects, which are generally avoided in structural materials due to their deleterious effect on strength.

Impact toughness at ambient and cryogenic temperatures was investigated with systematic fracture analyses for CuFeMn and Al15(CuFeMn)85 (at%) immiscible medium-entropy alloys. These two types of alloys exhibited different impact toughness behavior at different temperatures, while exhibiting higher impact toughness values than those of dual-phase steels with a similar strength level.

In the present study, the concept of maraging characteristics has been manipulated using a multistep thermomechanical approach involving isothermal aging and reversion treatments. Accordingly, a novel metastable maraging Fe68Ni10Mn10Co10Ti1.5Si0.5 (at%) medium entropy alloy has been designed and microstructurally engineered to achieve a heterogeneous medium entropy alloy decorated by (NiMn)3_xTix and n-Ni3Ti nanoprecipitates. Remarkably, the alloy exhibited an ultra-high yield strength of -1.3 GPa with a total elongation of -25.3% in the partially reversed sample, attributed to several aspects of microstructural heterogeneities, including the dual-phase microstructure, compositional gradient heterogeneity, and nano-precipitates. We proposed a prospective direction for the development of high-performance materials for structural applications through the microstructural engineering of Fe-based medium entropy alloy.

Maraging structural materials have been traditionally indicated as essential metallic alloys for hundreds of years. The highest strength of the aged martensite alloys requires the formation of high nanoprecipitate density; however, it often results in insufficient ductility (<-12%) which limits their application. Here, we describe how these alloys obtain enhanced ductility at high strength by injecting reversion-induced metastable austenite into the brittle microstructure, in which we develop a novel dual-phase medium-entropy Fe68Ni10Mn10Co10Ti1.5Si0.5 (at%) maraging alloys with a strength of 1.6 GPa and ductility of-25%. Generating the large fraction of austenite metastability with a chemical core-shell microstructure during a simple process of reversion drives profuse heterogeneities at chemical and structural states, including additional precipitation strengthening and transformation-induced plasticity effect. The combined metastability and heterogeneity, realized with heat treatment techniques that are accessible processing routes in a wide range of academic and industrial applications, can provide a breakthrough to develop sustainable maraging materials with large ductility.

In this study, the superplastic behavior and microstructural characteristics of the high pressure torsion-processed Al-15(CuFeMn)(85) immiscible medium-entropy alloy (IMMEA) were investigated. The multi-phase structure generated through spinodal-like decomposition in IMMEA played a key role in maintaining the ultra-fine structure and preserving an equiaxed shape during testing at high temperatures, ultimately leading to superplastic behavior. The IMMEA exhibited similar to 460% superplasticity at a strain rate of 10(-3) s(-1) and a temperature of 873 K (0.56 homologous temperature). This study is the first IMMEA superplasticity study and these results contribute to a better comprehension of the phenomenon.

Although Ti-containing medium-entropy alloys (Ti-MEAs) have the benefits of Ti such as low density, high specific strength, and oxidation resistance, their development is slow compared with Fe-based medium -entropy alloys (MEAs). Herein, a new class of Ti-MEAs was designed. Three equiatomic Ti-MEAs (TiVMo, TiZrMo, and TiVZrMo MEAs) were cast by vacuum arc melting. The solid solution formability of the newly designed Ti-MEAs was expected for diverse parameters, and the actual microstructures were systematically investigated. The TiVMo MEA formed a single phase with a body-centered cubic (BCC) structure. The TiZrMo and TiVZrMo MEAs had multiphase with dual BCC and Laves phases. The newly designed Ti-MEAs exhibited yield strengths from-1.1 to-1.6 GPa. In conclusion, a new domain of Ti-MEAs was discovered, and the experimental results could be a milestone for further designing Ti-MEAs. (c) 2022 Elsevier B.V. All rights reserved.

A novel maraging Fe68Ni10Mn10Co10Ti1.5Si0.5 (at%) medium-entropy alloy (MEA) was designed and microstructurally engineered to obtain a superior combination of tensile strength and uniform elongation at liquid nitrogen temperature. To this end, short-time martensite-to-austenite reversion treatment was conducted on an aged specimen to gain a dual-phase microstructure decorated by needle-like (NiMn)(3-x)Ti-x and the ellipticalshaped Ni2SiTi nano-precipitates. The alloy exhibited an ultra-high yield strength of 1.41 GPa and ultimate tensile strength of 1.88 GPa, with a uniform elongation of similar to 14% in the reverted condition. These superior properties are attributed to the transformation-induced plasticity (TRIP)-assisted heterogeneous dual-phase microstructure strengthened by well-distributed nano-precipitates. The metastability-engineering approach to achieve TRIP-assisted maraging MEA can usefully guide design to overcome the strength-ductility trade-off in extreme environments.

Cu–Fe alloys have drawn extensive attraction due to excellent multi-functional properties, including electrical, magnetic, and mechanical properties. However, the immiscible nature of Cu–Fe alloys results in heterogeneous microstructure and unexpected mechanical properties. In this study, a small amount of Zr was added to the cast Cu60Fe40 (wt