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The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well as typical deformation characteristics. The RHEAs with low density (7.41~7.51 g/cm3) have excellent compressive-specific yield strength ( σ YS / ρ) at 1023 K (~131 MPa·cm3/g) and 1123 K (~104.2 MPa·cm3/g), respectively, which are far superior to most typical RHEAs. And, they still keep appropriate plastic deformability at room temperature (ε > 0.35). The superior specific yield strengths are mainly attributed to the solid solution strengthening induced by the Zr element. The formation of the dislocation slip bands with [111](10 1 _ ) and [111](11 2 _ ) directions and their interaction provide considerable plastic deformation capability. Meanwhile, dynamic recrystallization and dislocation annihilation accelerate the continuous softening after yielding at 1123 K. [ABSTRACT FROM AUTHOR]

It remains challenging to develop low-cost body-centered cubic (BCC) high-entropy alloys (HEAs) with superior mechanical properties. In this work, we investigated the microstructure and mechanical properties of BCC FexCrNiAl0.5Ti0.5 HEAs containing L21 nanocrystals. With increasing the Fe content from Fe2 to Fe4 and Fe6, the formation of a big blocky L21 phase and a σ phase can be fully suppressed, and the size and fraction of the L21 crystals also decrease. Fe4 and Fe6 HEAs exhibit an optimized dual-phase microstructure with high-density L21 nanocrystals homogeneously distributed in the BCC matrix. Fe4 and Fe6 HEAs show high strength and do not fracture even at a large compressive strain of 70%, exhibiting the best combination of strength and fracture strain among all the reported BCC HEAs with nanocrystals. The superior mechanical properties of Fe4 and Fe6 HEAs are attributed to the optimized microstructure. These findings promote the development of low-cost HEAs with superior mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, heterogeneous L1 2 particles were successfully introduced into Ni 38 Co 25 Fe 13 Cr 10 Al 7 Ti 7 MPEA by two-stage aging treatment. Compared with the homogeneous particles, the heterogeneous L1 2 particles strengthened alloy exhibits enhanced strength-plasticity synergy. The tensile elongation is 23.2%, which is higher than all samples with the homogeneous particles, and the yield strength remains at 942 MPa, which is equivalent to the micro particles (972 MPa) with the highest yield strength in the homogeneous particles. Further analysis of the strengthening and deformation mechanisms revealed that precipitation hardening, and heterogeneous deformation-induced hardening were the main factors for the enhanced strength. The deformation-induced layered fracture networks, high-density Lomo-Cottrell locks, and heterogeneous L1 2 particles microstructure characteristics significantly improve the strain hardening ability; GNDs accumulate at the heterogeneous interface to alleviate the stress concentration at the GBs and improve the tensile plasticity of the MPEA with heterogeneous L1 2 particle structure. The heterogeneous L1 2 particle structure obtained through two-stage aging treatment without severe mechanical deformation has attractive engineering application potential. These properties of Ni 38 Co 25 Fe 13 Cr 10 Al 7 Ti 7 MPEA with heterogeneous L1 2 particle structure have important enlightening and practical value. • Designed and prepared Ni 38 Co 25 Fe 13 Cr 10 Al 7 Ti 7 MPEA with heterogeneous L1 2 particles. • Heterogeneous L1 2 particle structure obtained through simple two-stage heat treatment process. • The heterogeneous L1 2 particle reinforced alloy exhibits superior mechanical properties. [ABSTRACT FROM AUTHOR]

Solving the intermediate-temperature brittleness (ITB) of traditional superalloys and multi-principal element alloys (MPEAs) is a serious challenge. In this paper, a novel MPEA with superior mechanical performance is prepared and successfully overcomes the ITB by simple heat treatment. The effects of different solution treatments on the microstructure and mechanical properties of the alloy are studied. This work shows that the dendrite structure with trimodal γʹ structure is preserved by the subsolvus heat treatment. The heterogeneously distributed trimodal γʹ structure with high volume fraction primary γʹ phases in the interdendritic region effectively prevents the localized slip and enhances the pinning effect of grain boundaries, which inhibits the generation of ITB. The yield strengths of the MPEA with trimodal γʹ structure are 802 ± 17 MPa at 973 K, 814 ± 20.7 MPa at 1023 K and 776 ± 9 MPa at 1073 K, respectively, which are superior than that of most cast superalloys and MPEAs. Moreover, the elongations of the MPEA at 973 K, 1023 K and 1073 K are 10.6 ± 1.3 %, 14.2 ± 1.4 % and 11.0 ± 1.5 %, respectively, which increase by 214.9 %, 510 % and 219.4 %, respectively, compared with the MPEA with uniformly distributed bimodal γʹ structure. Meanwhile, the MPEA shows the best intermediate temperature plasticity (14.2 ± 1.4 %) at 1023 K due to the microstwinning. The scheme of combining MPEAs with the trimodal γʹ structure and microtwinning opens up a new avenue for the development and manufacture of advanced high-temperature structural materials. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) with superior mechanical properties have been considered as a potential next-generation candidate for high-temperature structural materials. However, the structural stability of RHEAs at high temperatures is still noncommittal so far. Especially, the Al containing RHEAs with coherent BCC/B2 microstructure usually form intermetallic phases following short/long term aging at elevated temperatures, which deteriorate the mechanical performance. In this work, we systematically determine the microstructural evolution, including intergranular precipitates, BCC/B2 morphology, and corresponding mechanical properties changes of the Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 RHEA from 923 K to 1123 K. The density of antiphase domain boundaries (APBs) in the RHEA after aging at 923 K is significantly higher than at 1023 K and 1123 K. Only a low volume fraction of tetragonal (Nb, Hf) 2 Al phase precipitates along grain boundaries after aging at 1123 K. However, the microhardness and yield strengths of the RHEA after aging at 923 K - 1123 K are close to those of the as-cast RHEA, which proves that the APBs and low-density (Nb, Hf) 2 Al precipitates have a negligible effect on the mechanical performance of the RHEA. Therefore, the Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 RHEA exhibits superior structural stability from 923 K to 1123 K, which also imparts the mechanical stability. This work guides towards tailoring the composition and microstructure of RHEAs for even better high-temperature mechanical performance. • The microstructural evolution of Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 has been explored. • APBs have a negligible effect on the mechanical performance of the RHEA. • Hf-rich segregations appear along GBs and in the matrix after aging at 1123 K. • Tetragonal (Nb, Hf) 2 Al phase precipitates along GBs after aging at 1123 K. • The RHEA shows superior structural and mechanical stability from 923 K to 1123 K. [ABSTRACT FROM AUTHOR]

Refractory high entropy alloys (RHEAs) with good high-temperature softening resistance have been revealed as promising candidates for high-temperature structural materials. In this work, a low-density ductile RHEA, Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 , has been developed. The RHEA with a BCC matrix and B2 nanoprecipitates exhibits excellent specific yield strength. The compressive specific yield strength (σ 0.2 /ρ) at 1073 K is as high as 83.2 MPa g−1 cm3. The different deformation behaviors during compression at 1073 K and 1273 K are also identified. The dislocation-dominated deformation provides the initial strain hardening capability, and then microcracks and dynamic recovery accelerate the transition from strain hardening to softening at 1073 K. While the diffusion-controlled dislocation annihilation and continuous dynamic recrystallization (DRX) are the dominant reasons for persistent strain softening at 1273 K. Our work not only reports a promising RHEA with excellent high-temperature properties, but also promotes the development of RHEAs for high-temperature applications. • A low-density ductile RHEA, Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 , has been developed. • The RHEA has BCC matrix and B2 nanoprecipitates. • The RHEA possesses the superior SYS (σ 0.2 /ρ = 83.2 MPa g−1 cm3) at 1073 K. [ABSTRACT FROM AUTHOR]

• The MIC of TiZrNb medium-entropy alloys (MEAs) was studied for the first time. • D. desulfuricans can induce the pitting of TiZrNb MEA underneath the biofilm. • Corrosion current density of MEA with D. desulfuricans was 12 times larger than that without D. desulfuricans. • D. desulfuricans prefer to acquire the electrons from Ti in MEA via an EET mechanism. The microbiologically influenced corrosion of TiZrNb medium-entropy alloys (MEAs) by Desulfovibrio desulfuricans was investigated. Pitting corrosion was found on coupon surface after 14-day immersion in the inoculated medium. Electrochemical tests demonstrated that the corrosion of coupon was enhanced by the D. desulfuricans. The corrosion current density (i corr) in the inoculated medium is approximately 12 times as much as that in the abiotic medium. In the presence of biofilms, the selective dissolution of Ti occurred, particularly when the organic nutrients were insufficient. Ti0 can be used as an electron donor by microbes in their energy metabolism once other donors are not readily available. [ABSTRACT FROM AUTHOR]

• A novel high specific strength plastic Ti 1.5 ZrNbAl 0.3 RHEAs was developed. • The tensile specific yield strength of this alloy is up to 145.5 MPa g−1 cm3. • The tensile fracture elongation of this alloy is up to 23.0%. • The specific yield strength-plasticity synergy is the best among all other RHEAs. • Short-rang orderings and cross-slip generate the strength-plasticity synergy. The ambient temperature brittleness and high density of refractory high entropy alloys (RHEAs) are the obstacles for their applications as structural materials. A novel ductile body-centered cubic Ti 1.5 ZrNbAl 0.3 RHEA with high specific strength was developed. The tensile specific yield strength and fracture elongation of this alloy are 145.5 MPa · g−1 · cm3 and 23.0%, respectively. The specific yield strength is the highest among all other reported RHEAs. The superior mechanical properties of the Ti 1.5 ZrNbAl 0.3 RHEA arise from the solid solution strength and cross-slip of dislocations. The ultrahigh specific yield strength and superior strength-plasticity synergy may promote the applications of RHEAs. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) have displayed numerous unique features, however, high strength and high ductility are still the urgently desired mechanical property. The current study reports an outstanding combination of high strength and excellent ductility achieved in a eutectic high-entropy alloy (EHEA) AlCoCrFeNi 2.1. The great achievement relays on a dual-phase heterogeneous structure strengthened with nano-precipitates. The heterogeneous structure provides the alloy a good combination of strength and ductility, and nano-precipitates in both of the face-centered cubic (FCC) and B2 phases generate an extra significant contribution to strength. Image, graphical abstract [ABSTRACT FROM AUTHOR]

One of the crucial issues in rechargeable zinc-air batteries is to explore low-cost, highly efficient bifunctional electrocatalysts for the oxygen reduction/evolution reaction. Here, the unique NiCo alloy nanoparticles encapsulated in the multi-dimensional nitrogen-doped carbon architecture (NiCo/MNC) is reported as an effective bifunctional catalyst for rechargeable zinc-air batteries. The multi-dimensional nitrogen-doped carbon architecture was synthesized through the rapid calcination of two-dimensional graphitic carbon nitride (g-C 3 N 4) and one-dimensional multi-walled carbon nanotubes (MWCNTs). The g-C 3 N 4 serves as the nitrogen source and the precursor for N-doped carbon nanosheets (NCSs). Simultaneously, NCSs can intertwine with MWCNTs to further obtain the multi-dimensional architecture with a large specific surface area. The synergistic effect between multi-dimensional nitrogen-doped carbon architectures and NiCo alloy nanoparticles endowed the NiCo/MNC with a positive half-wave potential of 0.83 V (vs. RHE: Reversible Hydrogen Electrode) for oxygen reduction reaction and a low potential of 1.61 V (vs. RHE) at the current density of 10 mA cm−2 for oxygen evolution reaction. Moreover, the zinc-air battery assembled with NiCo/MNC as the air-cathode exhibited a high-power density of 135.2 mW cm−2, a specific capacity of 701.7 mAh g−1, and an excellent stability in charging/discharging cycle test (over 115 h). The prepared catalyst could potentially serve to take the place of precious metal catalysts in rechargeable zinc-air batteries. Image 1 • NiCo alloy nanoparticles encapsulated in the multi-dimensional N-doped carbon (MNC) architecture was designed. • The synergistic effect between MNC and NiCo alloy nanoparticles can facilitate ORR/OER activities. • NiCo/MNC serves as an efficient ORR/OER catalyst for rechargeable zinc−air batteries. [ABSTRACT FROM AUTHOR]