Enhanced strength-ductility synergy in a V0.5Nb0.75Zr1.0Ti0.75 refractory high-entropy alloys by engineering heterogeneous microstructure

Abstract

The strength–ductility tradeoff remains a critical bottleneck limiting the practical applications of refractory high-entropy alloys (RHEAs). To address this issue, a novel V_0.5Nb_0.75Zr_1.0Ti_0.75 alloy with a bimodal grain structure was successfully fabricated through severe cold rolling (90 % reduction) followed by short-term annealing. The resultant microstructure comprised heterogeneous coarse grains (35 ± 8 μm) and nanoscale grains (197 ± 10 nm), both exhibiting identical BCC structure and uniform chemical compositions. The designed alloy exhibited exceptional strength–ductility synergy, including a tensile yield stress of 1060 ± 23 MPa and a fracture elongation of 23 ± 5 %, substantially exceeding previously reported results for most RHEAs. Detailed microstructural analysis revealed that the excellent ductility predominantly originated from the activation and accommodation of multiple dislocation slip systems within the coarse grains during initial deformation, while the high density of grain boundaries in the nanoscale grains effectively redistributed localized strain at large strains. Furthermore, pronounced solid-solution strengthening combined with grain-boundary strengthening effects primarily contributed by the nanoscale grains accounted for the superior strength. This work highlights the efficacy of heterogeneous microstructural engineering as a promising strategy to achieve a superior strength-ductility synergy in RHEAs.