Solid solution island of the Co-Cr-Fe-Ni high entropy alloy system

Single-phase equiatomic CoCrFeNi high entropy alloy (HEA) is a promising high-entropy base with high tensile ductility and fracture toughness. However, the equal molar fraction of these elements is not a sufficient and necessary condition to obtain a single solid solution with high entropies. Instead, our combination of both calculated phase diagram (CALPHAD) calculations and experimental verifications indicate that the single phase region in the Co-Cr-Fe-Ni HEA system can be extended from a point to a large single phase solid solution island. The significance of this study is that HEAs can be designed with a high design diversity.