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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]

Investigating the strength–plasticity synergy of metal structural materials is a crucial scientific challenge. This study focuses on preparing high-entropy alloys (HEAs) comprising Fe–Ni–Cr–Al, which exhibit a heterostructural coexistence of several phases through cold rolling and aging (CRA). Above 600 °C CRA, the average grain size of the HEA was refined from 260 to 1.64 μm, and numerous annealing twins were formed. Concurrently, two forms of irregularly ordered body-centred cubic (B2) phases and nanoscale ordered face-centred cubic (L1 2) phases were precipitated. Large B2 particles precipitated along the grain boundary, whereas small B2 and L1 2 particles precipitated within the grains. The average sizes of the B2 and L1 2 particles were 510 and 2.21 nm, respectively. The fine grain and precipitation strengthening enhanced the HEA yield strength (from 254 to 710 MPa). The difference in plastic strain between the matrix and precipitate causes long-range back-stress strengthening and heterodeformation-induced hardening, enhancing the strain-hardening ability and maintaining the superior plasticity of the HEA. This study provides an effective approach for obtaining metal structural materials with strength–plasticity synergy. • A FCC/L1 2 /B2 phases co-existed heterostructure HEA was designed. • The aging temperature changed the precipitation type of the second phase. • The mothod of deformation and thermal treatment obtained HEA of matching strength and plasticity. [ABSTRACT FROM AUTHOR]

The effect of Ti content on the microstructure and mechanical properties regulation for Fe 45 Ni 30−x Cr 15 Al 10 Ti x high entropy alloys (HEAs) with a duplex FCC/BCC structure is investigated. The as-cast Fe 45 Ni 30−x Cr 15 Al 10 Ti x HEAs have typical dendrite and inter-dendrite structure, where dendric and inter-dendric regions are FCC and BCC phases, respectively. After introducing Ti, the inter-dendric structure transforms into coexistence of disordered BCC and ordered B2/L2 1 phases. And the morphology of B2/L2 1 precipitates gradually changes from a regular maze-like mesh and cuboidal structure to elliptical structures due to the increase of the lattice mismatch. The change of precipitate type and volume fraction lead to that the ultimate tensile strength of the HEAs increases from 540 MPa to 1292 MPa. Meanwhile, it keeps the uniform elongation of 13.29%, showing outstanding strength-plasticity synergy. • A multi-phase coexistence HEA with superior mechanical property was designed. • The addition of Ti led to precipitation of hierarchical B2/L2 1 phase from BCC phase. • As the Ti content increased, the morphology of precipitates changed. [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]

• 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]