Effects of Cobalt on the structure and mechanical behavior of non-equal molar CoxFe50−xCr25Ni25 high entropy alloys

Non-equal molar high entropy alloys (HEAs) are promising to obtain better mechanical properties owing to abundant composition designs compared with single equal molar HEAs point. CoxFe50−xCr25Ni25 HEAs were designed to investigate the effect of Co compositional variation on the structure and mechanical properties of single phase solid solutions. Microstructure evolution at different strain levels was studied by electron backscatter diffraction. The results indicate that lattice parameter tends to decrease and yield strength are enhanced, with the increase of Co content. The ultimate tensile strength and ductility are improved at Co 30-35 at%, especially the ductility, compared to the equal molar CoCrFeNi HEAs. Meanwhile, grain rotation is slower and more difficult in non-equal molar Co35Fe15, and the greater low angle boundary fraction indicates the higher dislocation density. In different deformation stages, the dislocation forest strengthening and twinning-induced plasticity effect result in better strength-ductility combination in Co35Fe15.