Influence of V and Al in enhancing the strength and ductility of Co-rich high-entropy alloys

Since the proposal of face-centered cubic (fcc)-structured high entropy alloys (HEAs) almost two decades ago, multiple compositional combinations have been significantly developed, exhibiting exceptional mechanical properties. In this study, we propose a strategy for developing an fcc-structured Co-rich Co40Fe25V20Ni15 HEA by incorporating V instead of Cr to take advantage of its efficient strengthening effect. The newly developed HEA possesses solid-solution strength (σo) and Hall-Petch coefficient (ky) of 204 ± 13 MPa and 955 ± 60 MPa·µm1/2. The estimated ky is the highest amongst all fcc-structured HEAs and indicates a high grain boundary strengthening effect. Additional minor alloying with Al further enhances the mechanical performance of the alloy via precipitation-strengthening effects which exhibit comparable mechanical properties as Ni-based superalloys. Microstructural analyses of the deformation microstructures for the Al-free and Al-containing Co-rich samples reveal that deformation twinning is prevalent at 298 K and 77 K. The present study further demonstrates the importance of utilizing V and Al in developing high-performance alloys.