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TiAl alloys possess excellent properties, such as low density, high specific strength, high elastic modulus, and high-temperature creep resistance, which allows their use to replace Ni-based superalloys in some high-temperature applications. In this work, the traditional TiAl alloy Ti-48Al-2Nb-2Cr (Ti4822) was alloyed with additional Nb and fabricated using laser metal deposition (LMD), and the impacts of this additional Nb on the microstructure and mechanical and tribological properties of the as-fabricated alloys were investigated. The resulting alloys mainly consisted of the γ phase, trace β0 and α2 phases. Nb was well distributed throughout the alloys, while Cr segregation resulted in the residual β0 phase. Increasing the amount of Nb content increased the amount of the γ phase and reduced the amount of the β0 phase. The alloy Ti4822-2Nb exhibited a room-temperature (RT) fracture strength under a tensile of 568 ± 7.8 MPa, which was nearly 100 MPa higher than that of the Ti4822-1Nb alloy. A further increase in Nb to an additional 4 at.% Nb had little effect on the fracture strength. Both the friction coefficient and the wear rate increased with the increasing Nb content. The wear mechanisms for all samples were abrasive wear with local plastic deformation and oxidative wear, resulting in the formation of metal oxide particles. [ABSTRACT FROM AUTHOR]

Based on the advantage of rapid net-shape fabrication, laser powder bed fusion (LPBF) is utilized to process B4C-reinforced Ti composites. The effect of volumetric energy density (VED) on the relative density, microstructural evolution, tensile properties and wear behaviors of B4C-reinforced Ti composites were systematically investigated. The LPBF-ed samples with high relative density (>99%) can be achieved, while the pores and un-melted powders can be observed in the sample owing to the low energy input (33 J/mm3). The additive particulates B4C were transformed into needle-like TiB whiskers with nano-scale while C dissolved in the Ti matrix. Fine-scale grains (<10 μm) with random crystallographic orientation can be achieved and the residual stress shows a downtrend as the VED increases. Through the analysis of the tensile and wear tests, the sample at 61 J/mm3VED showed a good combination of strength and wear performance, with an ultimate tensile strength of 951 MPa and a wear rate of 3.91 × 10−4 mm3·N−1m−1. The microstructural evolution in VED changes and the corresponding underlying strengthening mechanisms of LPBF-ed Ti + B4C composites are conducted in detail. [ABSTRACT FROM AUTHOR]

Two different thermo-mechanical treatments (TMT) were performed on an alumina-forming austenitic (AFA) stainless steel, DAFA 29, which was recently developed at Oak Ridge National Laboratory for application in advanced ultra supercritical power plants. The resulting fine-grained TMT materials showed yield stresses more than double the yield stress of the as-received material at room temperature and more than 50% higher at 600 ºC, but lower yield stresses (but greater elongations) at 700 ºC and above. Strain rate jump tests performed at both 600 ºC and 700 ºC showed that the TMT materials have greater strain rate sensitivity and lower activation volumes at both temperatures. The strain rate has a power law relationship with the flow stress with a stress exponent of ~5. The as-received AFA alloy showed serrated stress–strain curves at 600 ºC suggesting the occurrence of dynamic strain aging. [ABSTRACT FROM AUTHOR]

As-cast nanostructured eutectoid Fe 28 Ni 18 Mn 33 Al 21 , which consists of ∼50 nm wide (Ni, Al)-rich B2 and (Fe, Mn)-rich fcc aligned phases, was annealed at 1173 K for various times up to 250 h in order to produce a wide range of phase widths (up to 2.5 μm) over which to evaluate the mechanical properties. The coarsening kinetics over these two orders of magnitude change could be described by r 2 − r o 2 = kt , where r is the phase width after time t at 1173 K, r o is initial phase width, and k is a constant. The yield strength, σ y , was found to follow a Hall–Petch-type relationship, i.e. σ y = σ o + k y λ −1/2 , where λ is the fcc phase width, σ o is the strength of the single-phase material, and k y is a constant. Interestingly, the work-hardening rate also roughly followed a λ −1/2 relationship, while the elongation to failure increased as λ increased from failure before yielding in the as-cast material to ∼7% for the material with the largest λ values. [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]

A high-N austenitic stainless steel (HNASS) was fabricated using a novel approach, in which duplex stainless steel powders were firstly gas nitrided in the temperature range of 700–900 °C and then consolidated using spark plasma sintering, resulting in an FCC matrix with average grain sizes of 1.6–8.2 μm. The Cr 2 N precipitates transformed from cellular precipitates (lamellar within the grains) to intergranular precipitation (equiaxed along the grain boundaries) as the nitriding temperature rose from 700 °C to 750 °C, and the N content rose from 0.68 wt% to 1.71 wt%. The 700 °C-treated alloy exhibits a yield strength of 783 MPa, a high tensile strength of 1091 MPa, and an elongation of 41% while the 900 °C-treated alloy exhibits an ultra-high compressive strength of 3017 MPa, and hardness of 520 HV. These values dramatically exceed the published values of similar HNASSs. Quantitative calculations showed that these superior mechanical properties could be attributed to increased solid solution and grain boundary strengthening. Furthermore, it can be inferred that while the equiaxed Cr 2 N phase increased the yield strength, it greatly degraded the fracture toughness. • A novel method, nitriding and followed spark plasma sintering, was used to fabricate HNASS. • The morphology of Cr 2 N phase changed from lamellar (within the grains) to equiaxed (along the grain boundaries). • The alloy features superior mechanical properties of yield strength (783 MPa) and ultimate tensile strength (1091 MPa). • Solid solution and grain boundary strengthening are dominant strengthening mechanisms. [ABSTRACT FROM AUTHOR]

• A phase-selective precipitation strategy is proposed to design a strong and ductile MEA. • Unique sequential deformation of L2 1 precipitates enables the strength-ductility synergy of MEA. • Deformation-induced L2 1 phase transformation reduces stress concentration, further stabilizing refinement of microbands. • Comprehensive simulations are employed to uncover the deformation mechanisms. • New insights into microstructural evolution and strain hardening guide the design of high-performance MEAs. Precipitation strengthening is paramount in the development of high-performance medium/high entropy alloys (M/HEAs). In this work, we showcase a phase-selective precipitation design applied to a (Ni 67.2 V 32.8) 90 Ti 5 Al 5 MEA to enable enhanced strength-ductility synergy. Upon annealing at 950 °C, multiple precipitates form in this MEA, including L2 1 , σ and hexagonal close packed (HCP) phases. However, an increase of 50 °C in annealing temperature removes most of the aforementioned precipitates except for the L2 1 phase. Density functional theory calculations are conducted to elucidate the formation mechanisms of phase-selective precipitation. Such selective approach to precipitation induces a brittle to ductile transition, increasing tensile elongation from 4 % to 43 % in our MEAs. Remarkably, the ultimate tensile strength of 1000 °C annealing MEA is maintained at ∼1.4 GPa, surpassing that of the precipitation-free Ni 67.2 V 32.8 base alloy (∼1.1 GPa), but with a comparable tensile elongation. Analytical models suggest that the increase in strength is attributed to both precipitation strengthening and grain refinement strengthening due to the pinning effect of precipitates. In particular, we investigate the complex deformation response of the L2 1 phase, which includes the formation of slip steps and a phase transformation from body-centered cubic (BCC) to body-centered tetragonal (BCT) structures, with the underlying mechanisms revealed through experimental characterization and molecular dynamics simulations. This co-deformation of matrix and L2 1 precipitates alleviates stress concentration at phase boundaries during straining and further maintains the microband-induced plasticity in the matrix till later deformation stage. All these result in the excellent strain hardening and thus, markedly enhancing ductility. Our findings pave new ways to craft strong and ductile M/HEAs by selecting hard-yet-deformable intermetallic precipitates. [Display omitted] [ABSTRACT FROM AUTHOR]

Titanium alloys produced by additive manufacturing show excellent mechanical properties at room temperature. However, their deformation behavior at low temperature is still not fully understood. In this study, the microstructural evolution and tensile behavior of the near-α titanium alloy Ti-6.5Al-2Zr-Mo-V (TA15), fabricated via laser powder bed fusion (LPBF), were determined at both 25 °C and −196 °C. The LPBFed TA15 alloy shows the microstructure of α laths and acicular α′ martensite due to the rapid cooling rate during LPBF processing. Pyramidal slip and numerous twins, including nano-twins and triple twins, were activated at cryogenic temperature, leading to the high ultimate tensile strength (UTS) up to 1750±8 MPa and yield strength (YS) up to 1548±25 MPa, which is higher than the strength at room temperature (YS∼1103 MPa, UTS∼1281 MPa). The dominant deformation mechanism changes from dislocation slip to twinning with decreasing temperature, leading to uniform deformation with an elongation of 5.2±0.1 %. The results can guide the control of the microstructure of LPBFed near-α titanium alloys at cryogenic temperature. • The LPBFed TA15 showed excellent tensile strength (YS∼1548 MPa, UTS∼ 1750 MPa, elongation∼5.2±0.1 %) at −196 °C. • A large number of 10 1 ̅ 1 < 10 1 ̅ 2 > nano-twins, including the nanotwins and triple twins, were activated at cryogenic temperature. • The dominant strengthening mechanism varies from dislocation strengthening to twin boundary strengthening. [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]

Abstract: The effects of different additions of chromium (≤8at. %) on both the microstructure and room-temperature flow and fracture behavior of as-cast Fe30Ni20Mn35Al15 have been investigated. For ≤6at. % Cr, the microstructure was lamellar consisting of (Ni, Al)-rich B2 and (Fe, Mn)-rich f.c.c. phases with most of the Cr residing in the f.c.c. phase, whilst the addition of 8at. % Cr produced a more complex microstructure. The room-temperature elongation to failure at a strain rate of 5×10−4 s-1 increased with increasing Cr from 6.5% for the Cr-free material to ~18% at 6at. % Cr, and then decreased dramatically for 8at. % Cr to 6.3%. Concomitantly, the yield stress decreased slightly from 820 to 679MPa as the Cr content increased to 6at. %, and then increased to 819MPa for 8at. % Cr. The addition of 6at. % Cr also resulted in the complete suppression of the environmental embrittlement that is observed at slow strain rate at room temperature in the Cr-free alloy [1], i.e. at a strain rate of 3×10−6 s−1 unalloyed Fe30Ni20Mn35Al15 showed only 0.7% elongation, whereas the alloy with 6at. % Cr exhibited 18% elongation. The 6at. % Cr modified alloy showed a similar temperature dependence of the yield strength as the Cr-free alloy [2], with the yield strength decreasing steadily to 150MPa at 1000K. Interestingly, the elongation to failure was largely independent of temperature for this alloy. [Copyright &y& Elsevier]

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]

Abstract This work systematically investigates the effect of carbon on the phase stability and room- temperature tensile performance of an annealed Fe 40.4 Ni 11.3 Mn 34.8 Al 7.5 Cr 6 (at%) high entropy alloy without (HEA) and with 1.1% carbon (CHEA). Four annealing conditions were investigated: 773 K for 13 d and 42 d, 973 K for 20 d, and 1073 K and 1423 K for 24 h. The resulting microstructures were analyzed using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and atom probe tomography (APT). Vickers hardness testing and room- temperature tensile testing were used to determine the mechanical properties of the annealed HEA and the CHEA. APT composition profiles revealed fine Ni,Mn,Al-enriched matrix precipitates in the CHEA annealed at 773 K for 13 d. After ageing at 773 K for 42 d, colonies of (Ni,Fe) 2 MnAl- enriched Heusler phase lamellae were observed at the grain boundaries (GBs) and in the matrix for the HEA, while GB lamellar colonies of Mn,Cr-enriched M 23 C 6 carbides were observed for the CHEA. Due to the presence of the GB carbides, the resulting room-temperature elongation to fracture for the CHEA annealed at 773 K for 42 d was ~1% compared to ~11% for the HEA given the same anneal. At higher annealing temperatures, the microstructure contains Ni,Al-rich and Mn,Cr,C-rich precipitates that alternate along the GBs and appear to be associated with each other in the matrix. Electron diffraction analysis indicates the aforementioned Ni,Al-precipitates and Mn,Cr-carbides have b.c.c. and f.c.c. crystal structures, respectively. Once again, a low elongation to fracture (2%) was seen for the carbon-containing material compared to its un-doped counterpart (23%) which solely contained Ni,Al-rich b.c.c. precipitates. [ABSTRACT FROM AUTHOR]

A novel vanadium-doped f.c.c. medium-entropy alloy (MEA) Ni 42.4 Co 24.3 Cr 24.3 Al 3 Ti 3 V 3 was designed to achieve excellent cryogenic mechanical properties. The vanadium was added in order to increase the temperature-dependent friction stress, and aging of the MEA, which had been given a homogenization anneal at 1150 °C followed by cold-rolling to 80% reduction, at 700–900 °C was used both to produce partial recrystallization and precipitate L1 2 nanoparticles. Aging produced a heterogeneous microstructure composed of fine, soft recrystallized grains surrounded by harder, relatively-large non-recrystallized grains, containing L1 2 -precipitates. Increasing the aging temperature from 700 °C to 900 °C promoted V partitioning into the f.c.c. matrix with the partitioning coefficient increasing from 0.8 to 1.9; the grain size increasing from 2.3 μm to 4.6 μm; an increase in the precipitate size from 10.5 nm to 80.0 nm; a reduction in the residual geometrically-necessary dislocation (GND) density from 9.0 × 1014 m−2 to 2.8 × 1014 m−2; and a decrease in the volume fraction of precipitates fraction from 28% to 14%. All three aged MEAs showed extraordinary cryogenic mechanical properties with an increase in the aging temperature resulting in an increase in strength but a decrease in ductility, viz, a yield strength (YS) of 1929 MPa, an ultimate tensile strength (UTS) of 2147 MPa, and an elongation to failure (ε) of 6.6% at 700 °C, YS ∼ 1735 MPa, UTS ∼ 1976 MPa, ε ∼ 9.0% at 800 °C, and YS ∼ 1274 MPa, UTS ∼ 1694 MPa, ε ∼ 24.8% at 900 °C. The dislocation back stress rose progressively with increasing strain and was invariably higher than the effective stress, accounting for 51–59% of the flow stress i.e. the back stress played a dominant role in the ultrahigh flow stress. Increasing the aging temperature also produced a greater abundance of nanoscale deformation twins, stacking faults, and dislocation networks, which are responsible for excellent strain hardening capacity and greater ductility. After deformation, the density of low-angle grain boundaries increased by 3–6 times to 0.6–1.3 μm/μm2, and the GND density increased by 4–6 times to 1.2–2.0 × 1015 m−2. • V addition enhanced the cryogenic strength by 240–290 MPa and dcreased elongation. • V partitioned to the f.c.c. matrix instead of L1 2 -precipitates and thus improved friction stress. • MEA shows exceptional YS of 1274–1929 MPa, UTS of 1694–2147 MPa, and elongation of 6.6–24.8% at 77 K. • Increasing aging temperature produced more deformation twins, stacking faults, and dislocation networks. • Back-stress account for 51–59% of flow stress and was invariably higher than effective stress. [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]

The strength-ductility trade-off has always been a difficult issue in the development of highperformance structural materials. In this work, a new non-equiatomic Fe 37.5 Ni 30 Co 22.5 Al 5 Ti 5 (at%) high entropy alloy (HEA) was developed, which shows both excellent strength and ductility. The yield strength of the aged HEA reached 1094 MPa, which is more than twice that of the solid-solution HEA, while the ultimate tensile strength was 1275 MPa, and the elongation to failure was ∼38%. The high yield strength resulted from precipitation strengthening provided by a high number density of L1 2 -Ni 3 (Al, Ti) nanoprecipitates. Both a small grain size and the nanoprecipitates can induce high local stresses, enhancing the phase transformation from face-centered cubic (FCC) to martensite that occurs in this HEA, and which can lead to the good ductility. As much as possible to keep strength-ductility through the coupling between precipitation strengthening and TRIP effect is a suitable strategy to overcome the strength and ductility trade-off. • The yield strength of the aged HEA is more than twice that of the solid-solution HEA with the elongation loss of only ∼19 %. • Under the coupling between precipitation strengthening and TRIP effect, the AG HEA shows excellent mechanical properties. • The nanoprecipitates change the SFE of the matrix and promote the occurrence of phase transformation to some extent. [ABSTRACT FROM AUTHOR]

Both a novel Ti-5Cu alloy (in wt%) and a Ti-5Cu in situ composite containing 1 wt% B 4 C were fabricated by laser powder bed fusion, and their microstructures, mechanical and tribological properties were systematically investigated. The microstructure of the Ti-5Cu was mainly composed of α Ti laths, Ti 2 Cu and retained β phases, while the B 4 C/Ti-5Cu composite was composed of α Ti laths, Ti 2 Cu, TiC, TiB and TiB 2 phases. Both the Cu and B 4 C additions promoted a transition from columnar to equiaxed grains for prior-β and α phases. The B 4 C/Ti-5Cu composite was found to have a higher hardness (467 HV) than the Ti-5Cu (417 HV). Further, the composite exhibits a yield strength of 1100 MPa and an ultimate tensile strength of 1250 MPa. Values which are higher than those of the Ti-5Cu that exhibits a yield strength of 750 MPa and an ultimate tensile strength of 900 MPa. However, this strength increase comes at the expense of a reduction in elongation to failure from 6.2% to 1.5%. Even though the composite is significantly stronger, the two materials exhibited very similar wear rates (ω B4C/Ti-5Cu = 4.95 × 10−4 mm3 N−1 m−1 and ω Ti-5Cu = 4.85 × 10−4 mm3 N−1 m−1). • The LPBFed Ti-5Cu was mainly composed of α Ti laths, Ti 2 Cu and retained β phases. • The LPBFed B 4 C/Ti-5Cu composite was composed of α Ti laths, Ti 2 Cu, TiC, TiB and TiB 2 phases. • Both the addition of Cu and B 4 C can refine the grain and promote columnar to equiaxed transition of prior-β phase. • The LPBFed Ti-5Cu exhibit a strong combination of hardness, tensile properties and wear resistance. • Although the composite is significantly stronger, the two materials exhibited very similar wear rates. [ABSTRACT FROM AUTHOR]

In this paper, we describe the effects of different scanning speeds (600–900 mm/s) on the microstructure, mechanical properties and corrosion behavior of biodegradable bone-substitution alloys produced from 80:20 (by wt.) Fe:Mn powders using laser powder bed fusion (LPBF). Both the Mn content (18.9–15.1 wt% Mn) and density (7920–7730 kg/m3) of the LPBFed samples decreased slightly with increasing laser scanning speed, while the oxygen content increased (0.12–0.40 wt%). Increasing scanning speed also led to increased porosity (from 0.27% to 2.5%) and increased cracking. The specimen produced at the lowest scanning speed of 600 mm/s, which consisted of only the HCP ε-martensite phase, showed by far the highest yield strength (YS) at 644 MPa and the highest ultimate tensile strength (UTS) at 857 MPa, but the lowest elongation to failure (El) of only 13.7%. Specimens produced at higher scanning rates consisted of both BCC α′-martensite and ε-martensite phases. The sample fabricated at a scanning speed of 700 mm/s showed the best balance of mechanical properties with a YS of 330 MPa, a UTS of 839 MPa, and an El of 36.1%. Electrochemical testing showed corrosion rates from 0.09 mm/yr (600 mm/s specimen) to 0.22 mm/yr (700 mm/s specimen), which are higher than those of both pure Fe and most Fe–30Mn and Fe–35Mn alloys reported in the literature. The work demonstrates that the meso-/micro-scale structure, and, hence, the mechanical properties and corrosion rates of Fe–Mn alloys can be tailored by varying the scanning speed during LPBF processing. It also demonstrates the potential of LPBFed Fe–Mn alloys with low Mn content for use as biodegradable bone substitutes. [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]

• AlSi10Mg components were fabricated by SLM under different VED ranges, i.e. conduction, transitional, and keyhole modes. • The KDP was consisted of α-Al, with less than 15 μm grain size, and enclosed by ~200 nm eutectic Si cellular networks. • No preferential crystallographic orientation could be observed within the KDP. • The high-stress exponents indicate that the creep behavior is controlled by dislocation-particle interactions. • The SLM AlSi10Mg fabricated in the transition mode exhibits a high tensile strength combined with reasonable ductility. The effect of the volumetric energy density (VED) on the keyhole formation, microstructural evolution and associated mechanical properties of AlSi10Mg fabricated by selective laser melting (SLM) has been systematically investigated. The results indicated that three melting modes could be distinguished during the laser melting process, corresponding to different VED ranges, i.e. conduction mode (<50 J mm-3), transitional mode (~50–65 J mm-3), and keyhole mode (>65 J mm-3). A high VED not only produced keyhole defects and hydrogen pores, but also generated two types of molten pool, i.e. a general shallow molten pool (GSP) and a keyhole-induced deep molten pool (KDP). The GSP was mainly consisted of an α-Al matrix, with ~30 µm grains size, and enclosed by a ~500 nm eutectic Si cellular network. The grain size of the KDP was less than 15 µm, and it has both a finer Si network (~200 nm) and nano-scale Si particles. No preferential crystallographic orientation could be observed within the KDP, while a strong texture along<111>orientation was exhibited in the GSP. These were responsible for the different mechanical properties of the SLM parts under different melting modes. The related mechanisms of the GSP and the KDP formation are comprehensively discussed and a correlation between the microstructure and the mechanical properties is also outlined. [ABSTRACT FROM AUTHOR]