Impact of different Cr contents on microstructural evolution and mechanical behaviour of CoCrxCuFeMnNiV high-entropy alloys

The CoCrxCuFeMnNiV (x = 0, 0.25, 0.5, 0.75, 1) high-entropy alloy was prepared via vacuum arc smelting, and the effect of different Cr contents on the microstructure evolution and mechanical properties of it was evaluated. The results show that the CoCuFeMnNiV alloy is composed of FCC1+FCC2 phases, while Cr-added CoCrxCuFeMnNiV alloy is composed of FCC1+FCC2+sigma phases; moreover, the amount of sigma phase increases with the Cr content. Through calculations, a phase formation criterion suitable for the CoCrxCuFeMnNiV alloy was established. It was observed that adding Cr does not affect the early solidification behaviour of the FCC1 and FCC2 phases; however, it affects the stability of the FCC1 phase and promotes the transformation of this phase into the sigma phase, as well as secondary precipitation of a nanoscale copper-rich phase on this phase. The formation of sigma phase has a significant strengthening effect on the alloy but reduces its plasticity. The CoCr0.5CuFeMnNiV alloy has favourable comprehensive properties; specifically, its yield strength, compressive strength, microhardness, and fracture strain are 820 MPa, 1050 MPa, 320 HV, and 22.5%, respectively. With an increase in Cr content, the alloy fracture mode changes from ductile to brittle