Temperature-dependence of phase-selective recrystallization in eutectic high-entropy alloy and its mechanical effects

Abstract

Phase-selective recrystallization (PSR) is an effective strategy for improving the mechanical properties of eutectic high-entropy alloys (EHEAs). Via PSR treatment, the recovered hard phase and the recrystallized soft phase work together to fully release the strain-hardening capacity of EHEAs. However, few studies have focused on optimizing the PSR structures in EHEAs. In this study, we systematically investigated the effect of annealing temperature and rolling times on the PSR of Ni₄₄Co₁₀Cr₁₂Fe₁₅Al₁₇W₂ EHEA and obtained the processing window in PSR. At a lower annealing temperature of 800 °C, the annealed sample maintained a lamellar structure with both FCC and B2 phases recovered. As the annealing temperature increased to 1000 °C, the fully recrystallized FCC phase and the recovered B2 phase, that is, the PSR structure, were obtained after the second cold rolling and subsequent annealing. At 1200 °C, both FCC and B2 phases recrystallized into equiaxed grains. The PSR sample showed a doubled ductility of 27 % and a similar yield strength of 868 MPa compared to the as-cast sample. Our strengthening and fracture mechanisms analysis showed that the high strength of PSR EHEA mainly came from the boundary-strengthening of the lamellar structure, and the reduced crack nucleation sites caused by the PSR structure ensured its excellent ductility. These findings indicated that the properties of the EHEA could be further improved using PSR treatment for a wide range of engineering applications.