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In the quest to enhance the mechanical properties of CuP alloys, particularly focusing on the Cu3P phase, this study introduces a comprehensive investigation into the effects of various alloying elements on the alloy's performance. In this paper, the first principle of density universal function theory and the projection-enhanced wave method under VASP 5.4.4 software are used to recalculate the lattice constants, evaluate the lattice stability, and explore the mechanical properties of selected doped elements such as In, Si, V, Al, Bi, Nb, Sc, Ta, Ti, Y and Zr, including shear, stiffness, compression, and plasticity. The investigation reveals that strategic doping with In and Si significantly enhances shear resistance and stiffness, while V addition notably augments compressive resistance. Furthermore, incorporating Al, Bi, Nb, Sc, Ta, Ti, V, Y, and Zr has substantially improved plasticity, indicating a broad spectrum of mechanical enhancement through precise alloying. Crucially, the validation of our computational models is demonstrated through hardness experiments on Si and Sn-doped specimens, corroborating the theoretical predictions. Additionally, a meticulous analysis of the states' density further confirms our computational approach's accuracy and reliability. This study highlights the potential of targeted alloying to tailor the mechanical properties of Cu3P alloys and establishes a robust theoretical framework for predicting the effects of doping in metallic alloys. The findings presented herein offer valuable insights and a novel perspective on material design and optimization, marking a significant stride toward developing advanced materials with customized mechanical properties. [ABSTRACT FROM AUTHOR]

High-nitrogen stainless steel (HNSS) has been widely concerned and studied owing to its excellent mechanical, corrosion resistance, and biocompatibility properties. A series of HNSS was prepared by metal injection molding (MIM) using gas atomized Fe–Cr–Mn–Mo–0.3 N duplex stainless steel powders. Both sintering and solution treatments were carried out in an N2 atmosphere. The effects of nitrogen distribution and phase transformation on the mechanical properties of MIM HNSS during sintering and solution were studied. The results show that as the sintering temperature increased, the sample density increased, but the total nitrogen content decreased. Nitrogen and Cr2N concentration gradients along the cross-section of as-sintered samples were formed after cooling. The high nitrogen content promotes the decomposition of γ: γsaturated translated to γ and Cr2N. Meanwhile, the low Mn content in austenite also decomposes γ: γ translated to α and Cr2N. After solution treatment, a single γ phase was obtained for samples sintered at 1200 to 1320 °C. For solution treatment samples sintered at 1320 and 1350 °C, their tensile strength was 988.76 and 1036.12 MPa; yield strength was 615.61 and 636.14 MPa, and elongation was 42.58 and 40.08%, respectively. These values vastly exceeded the published MIM HNSS values. [ABSTRACT FROM AUTHOR]

The thermal stability of the coherent, nanoscale, L1 2 precipitates and fine grains in a strong, ductile medium-entropy alloy (MEA) Ni 43.4 Co 25.3 Cr 25.3 Al 3 Ti 3 were analyzed and related to the room-temperature mechanical properties. Increasing the aging temperature and prolonging the soaking time produced more L1 2 precipitates and reduced the matrix lattice constant. The fine grains exhibit excellent thermal stability with a very low coarsening rate (1.73 × 10−24 m3/s at 700 °C, 4.78 × 10−23 m3/s at 800 °C, and 4.32 × 10−22 m3/s at 900 °C), which mainly results from the strong pinning from the high density of precipitates and high activation energy for grain growth (∼272 kJ/mol). The L1 2 precipitates remain spherical and have a coherent relationship with the matrix during ripening from tens to hundreds of nanometers. They exhibit better thermal stability (6.45 × 10−30 m3/s at 700 °C, 2.03 × 10−28 m3/s at 800 °C, and 7.16 × 10−27 m3/s at 900 °C) than the L1 2 precipitates in nickel-based superalloys by 1–2 orders of magnitude with an activation energy of 341 kJ/mol. The critical size for the transition from dislocation shear of the L1 2 precipitates to dislocation looping is 23.5–30.4 nm. No significant coarsening of either the grain size or L1 2 precipitates caused a small decrease in the YS and UTS of MEA aged at 700 °C. In comparison, both the YS and UTS of MEA aged at 800–900 °C dramatically decreased, which is caused by the coarsening of the L1 2 nanoparticles and the average grain size. This decrease in strength was accompanied by a slight increase in ductility at all three aging temperatures. • Activation energy for L1 2 precipitates growth of 341 kJ/mol caused good thermal stability. • High dense precipitates resulted in strong pinning pressure for fine grains coarsening. • Activation energy for grain growth is as high as 272 kJ/mol. • Transition from dislocation shearing/looping L1 2 precipitates is 23.5–30.4 nm. • Significant coarsening of grains and L1 2 precipitates occurs at 800–900 °C. [ABSTRACT FROM AUTHOR]

The microstructure, room-temperature deformation mechanisms, and weldability of the medium-entropy alloy (MEA) NiCoVAl 0.2 have been investigated. Defect-free welded joints have been produced with good mechanical properties, indicating excellent weldability. The microstructure consists of f.c.c. grains containing many b.c.c. Ni 2 VAl (Ni 26.1 Co 33.5 V 27.8 Al 12.6) and few σ-type precipitates (Ni 15.5 Co 21.3 V 62.7 Al 0.5). Decreasing the aging temperature from 1100 °C to 900 °C, produced a higher area fraction of Ni 2 VAl precipitates (8 → 25%), much smaller L2 1 precipitates (7.2 → 1.4 μm), finer grains (17.1 → 2.4 μm), and presence of σ-type precipitate, resulting in simultaneous improvements in both the strength and ductility for both the thermo-mechanically treated (TMT) and electron beam welded (EBWed) MEA. The TMT MEA shows an excellent combination of strength (YS∼993 MPa, UTS∼1478 MPa) and ductility (30.3%), while the EBWed MEA shows slightly lower strength (YS∼822 MPa, UTS∼1194 MPa) and significantly reduced ductility (12.3%), i.e. a YS, UTS, and ductility of 83%, 81%, and 41%, respectively, of those of the TMT MEA. With increasing strain, both low-angle grain boundaries and geometrically-necessary dislocation (GND) densities increased. The TMT MEA has a higher GND density (1.6 × 1015 m−2) than the 9.1 × 1014 m−2 of EBWed MEA after strained to fracture. For both the TMT and EBWed MEA aged at 900 °C, the deformation was accommodated by dislocation slip, dislocation looping around precipitates, and nano-twinning. However, for both the TMT and EBWed MEA aged at 1100 °C, more abundant deformation twinning and an fcc→hcp shear transformation appeared, which may originate from a lower stacking fault energy due to differences in the f.c.c. matrix composition. [ABSTRACT FROM AUTHOR]

The microstructures and deformation mechanisms of the f.c.c. medium-entropy alloy (MEA) (NiCoCr) 76 (Ni 6 AlTi) 3 has been analyzed after various thermo-mechanical treatments. The solutionized, single-phase MEA, which had a grain size of 93.4 ± 31.9 μm, was cold-rolled (CR) to a 80% thickness reduction after which it showed both a high yield strength (YS) of 1539 MPa and a high ultimate tensile strength (UTS) of 1602 MPa, but an elongation to failure, ε, of only 16%. The CR MEA was then subjected to one of two heat treatments: (1) the CR MEA was recrystallized at 1100oC for 24 h, which produced a single-phase material with 85 ± 61.7 μm grain size that exhibited a much lower YS and UTS of 364 MPa and 747 MPa, respectively, but a much greater ε of 73%; and (2) the MEA was aged at 700oC for 24 h, which produced a fine-grained (1.1 ± 0.9 μm) material and a high volume fraction (0.35) of 12 nm dia. L1 2 nanoparticles that exhibited an excellent combination of strength and ductility, viz., YS∼1501 MPa, UTS∼1651 MPa, elongation ∼26%. The grain boundary strengthening and precipitation strengthening were together estimated to account for ∼58% of the YS in the latter material. After deformation, the recrystallized MEA contained numerous stacking faults and a Taylor lattice structure containing domain boundaries and microbands, while the aged MEA exhibited numerous stacking faults and sheared particles. The density of low-angle grain boundaries (LAGBs) in the recrystallized MEA increased by 100 times to 2.2 × 10−1 μm/μm2 while the density of CSL Σ3n boundaries decreased by 71% to 7.8 × 10−3 μm/μm2 after deformation. In contrast, the density of LAGBs in the aged MEA increased by 5 times to 2.6 μm/μm2 while the density of CSL Σ3n boundaries decreased by 57% to 0.6 μm/μm2 after deformation. [ABSTRACT FROM AUTHOR]

A strong, ductile medium-entropy alloy, MEA, (CoCrNi) 94 Al 3 Ti 3 with few defects was fabricated using the selective electron beam additive manufacturing technique. Due to preheating the substrate at 1173 K, the as-printed MEA showed coherent L1 2 nanoparticles (dia.∼112 nm, volume fractioñ8.9 %) in 68 μm grains with a dual {100}<011> + {100}<001> texture. The as-built alloy exhibited a yield strength (YS) of 612 MPa, an ultimate tensile strength (UTS) of 1020 MPa, and an elongation to failure (ε) of 37 % at 298K. These values increased when testing was at 77 K, i.e. YS of 811 MPa, UTS of 1339 MPa, and an ε of 39 %. After tensile failure, the LAGBs and GND densities sharply increased at both temperatures to accommodate strain gradient along with <111> fiber texture. The lack of annealing twin boundaries led to a relatively low strain hardening rate (SHR) of 2500 MPa at 298 K and 3890 MPa at 77 K (at 5 % strain) as compared to values of thermo-mechanically processed (CoCrNi) 94 Al 3 Ti 3. The SHR curves exhibited three distinct stages, where an abrupt upturn at an intermediate strain level can be attributed to the occurrence of DTs and SFs at 77 K, and the appearance of SFs at 298 K. • A strong, ductile MEA (CoCrNi) 94 Al 3 Ti 3 was fabricated using SEBM additive manufacturing. • As-printed MEA showed L1 2 nanoparticles (dia.∼112 nm, f∼8.9 %) within 68 μm grains with dual textures. • As-printed MEA shows excellent cryogenic mechanical properties with YS of 811 MPa, UTS of 1339 MPa, and ε of 39 %. • Lack of annealing twins led to a relatively low strain hardening rate of 2500 MPa at 298 K and 3890 MPa at 77 K. • Deformation twins and stacking faults caused substantial increase in strain hardening rate at 77 K. [ABSTRACT FROM AUTHOR]

Influences of both aging temperature and vanadium addition on the microstructure and mechanical properties of a nanoparticle-strengthened, partially-recrystallized, medium-entropy alloy (MEA) Ni 43.4 Co 25.3 Cr 25.3 Al 3 Ti 3 were probed in the present work. Aging (700 °C or 900 °C) produced both a high density of nano-sized L1 2 precipitates, and a heterogeneous grain structure, which consisted of fine soft recrystallized grains surrounded by harder relatively large unrecrystallized grains. The volume fraction and size of the nanoparticles were strongly dependent on the heat treatment, as was the partitioning of the V, i.e. , almost evenly distributed between the f.c.c. matrix and L1 2 precipitates at 700 °C but partitioned more to the f.c.c. matrix with a coefficient of 1.9 at 900 °C. The yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (ε) simultaneously increased with decreasing temperature from 298 K to 77 K. The V-doped MEA shows an excellent combination of strength and elongation, viz. YS of 1035∼1637 MPa, UTS of 1587∼1983 MPa, and ε of 17.6–37.7 % for the V-free MEA, and YS of 1274∼1929 MPa, UTS of 1694∼2147 MPa, and ε of 6.6–24.8 % for V-doped MEA. The excellent strength of the MEA resulted from a combination of back-stress hardening (1108–1195 MPa corresponding to 51–60 % of the flow stress), Hall-Petch strengthening, and hardening from pre-existing dislocations (199–355 MPa) at 298 K and 77 K. Increasing the aging temperature promoted a transition in the deformation behavior from heterogeneous to homogeneous, and produced a greater abundance of nanoscale deformation twins, stacking faults, and dislocation networks, leading to the exceptional monotonic decreased strain-hardening rates during tensile tests at 293 K and 77 K. • Vanadium addition could improve friction stress and overall strength of the present MEA. • Vanadium partition behavior between f.c.c. and L1 2 nanoparticles could be significantly influenced by aging temperature. • V-free MEA shows an YS of 1035∼1637 MPa, UTS of 1587∼1983 MPa, and ε of 17.6–37.7 %. • V-doped MEA shows an YS of 1274∼1929 MPa, UTS of 1694∼2147 MPa, and ε of 6.6–24.8 %. • Back-stress hardening of 1108∼1195 MPa corresponding to 51–60 % of the flow stress at 77 K [ABSTRACT FROM AUTHOR]

The weldability, microstructures, and mechanical properties of two L1 2 -nanoparticle-strengthened medium-entropy alloys (MEAs) Ni 43.4 Co 25.3 Cr 25.3 Al 3 Ti 3 and Ni 42.4 Co 24.3 Cr 24.3 Al 3 Ti 3 V 3 (at.%) are explored after electron beam welding (EBW). Strong yet ductile defect-free joints were produced with coarse columnar grains (118–245 μm) in the fusion zones, which were larger than the equiaxed grains in the heat-affected zones (15.6–22.3 μm) and in the base materials (4.6–5.6 μm). Both EBWed MEAs showed high yield strengths (838–858 MPa), high ultimate tensile strengths (1416–1420 MPa), and good fracture strains of 20–21 % at 77 K, which are 66∼83 %, 84–89 %, and 57–81 %, respectively, of those of the respective thermo-mechanically treated (TMT) MEAs. The V-doping improved the cryogenic mechanical properties of the TMT MEA while not influencing those of the EBWed MEA. High back-stress hardening contributes to over 50 % of the cryogenic strength. Both EBWed MEAs exhibited abundant dislocation networks, stacking faults, and nanoscale deformation twins after fracture, producing a high strain hardening rate and good ductility. [ABSTRACT FROM AUTHOR]

A novel f.c.c. (CoCrNi) 94 Al 3 Ti 3 medium-entropy alloy strengthened with an L1 2 phase was designed using CALPHAD. Hot rolling, cold rolling, and heat treatment were used to produce a fine grain size (0.61 μm) and a high volume fraction (0.37) of coherent 23.2 nm diameter L1 2 nanoparticles. This tailored microstructure exhibited an excellent strength-ductility synergy (yield stress∼1203 MPa, ultimate tensile strength∼1577 MPa, elongation ∼24%) and a high working hardening rate (3700 MPa at strain of 5%). The contributions from grain boundary strengthening and precipitation strengthening to the yield strength were estimated to be ∼61%. After the tensile tests, the fraction of LAGBs sharply increased and that of Σ3n coincidence site lattice boundaries decreased: inverse pole figures indicate the formation of a {101}<111> texture. Such an ultrafine grain size suppressed deformation twinning, while applied stress led to a higher density of geometrically-necessary dislocations at the grain boundaries compared to the grain interiors. [Display omitted] [ABSTRACT FROM AUTHOR]

Electron beam welding of the medium-entropy alloy (MEA) (NiCoCr) 94 Al 3 Ti 3 to 304 stainless steel (SS) has been undertaken. Defect-free joints were obtained with coarse columnar grains: the columnar grains on the 304 SS side of the fusion zone (FZ) were finer (94 μm, length-to-width ratio∼2.7) than the grains on the MEA side (204 μm, 2.9), a difference that probably resulted from a higher cooling rate after welding due to the higher thermal conductivity of the 304 SS compared to the MEA. Mixing of the two materials in the FZ led to lower vol.% (14%) and larger diameter (44 nm) of L1 2 nanoparticles compared to the 23 nm dia. and 37% vol.% in the aged MEA, a result consistent with CALPHAD analysis. The joint showed a good combination of yield strength (323 MPa), ultimate tensile strength (670 MPa), and elongation (24%). Failure occurred by ductile fracture in the FZ. [Display omitted] [ABSTRACT FROM AUTHOR]

The weldability and effects of subsequent heat treatment on the microstructure and mechanical properties of the medium-entropy alloy (MEA) (NiCoCr) 94 Al 3 Ti 3 have been explored using electron beam welding (EBW). It was found that EBW joints consist of a supersaturated f.c.c. matrix with coarse, asymmetric columnar grains (17.7–24 μm). The fraction of twins and Σ3n CSL boundaries in weld joints was only 10% of that in the base metal, a value which increased to 30% after aging at 800 °C. The aging also led to improvements in the hardness, tensile strength, and work hardening rate, a result of the precipitation of a high volume fraction (0.29–0.33) of ultrafine (15–17.4 nm dia.) coherent spherical L1 2 -structured particles. The contributions of the L1 2 nanoparticles and Hall-Petch strengthening to the yield strength were estimated to be 537–573 MPa and 105–123 MPa, respectively. The MEA shows excellent weldability and, after aging, good strength (YS∼1098 MPa, UTS∼1368 MPa) and elongation to failure (∼11%) by ductile fracture. • Electron beam weld joints consist of supersaturated f.c.c. phase with asymmetric coarse columnar grains. • Aging treatment following EBW leads to precipitation of L1 2 nanoparticles in the weld joint. • Precipitation of L1 2 nanoparticles results in a dramatic improvement in hardness, strength, and work hardening rate. • EBW MEA shows good weldability and strength-ductility synergy (YS∼1098 MPa, UTS∼1368 MPa, E∼11%). [ABSTRACT FROM AUTHOR]