Evolution of Substructure of a Non-equiatomic FeMnCrCo High Entropy Alloy Deformed at Ambient Temperature

The present investigation aims at discerning the evolution of microstructure of a Fe₄₀Mn₄₀Cr₁₀Co₁₀ high entropy alloy, under uni-axial loading at room temperature. At the time of quasi-static uni-axial loading, the alloy exhibited an ultimate tensile strength of ~ 514 MPa with fracture strain of ~ 47 pct. Multiple stages of work hardening were observed during the deformation. The initial work hardening of the alloy, for the true strain of ɛ ~ 0.05 to 0.1, was facilitated by the rigorous planar slip of dislocations. Extensive cell formation in the mid-strain levels, i.e., for ɛ ~ 0.1 to 0.29, resulted in overall softening. The onset of microband formation was also observed during the mid-strain level, which further got populated in large numbers during the final stage of deformation. Simultaneous occurrence of twins as well as deformation induced FCC → HCP phase transformation was observed in the grains oriented along TD//〈111〉 in the fractured specimen. Highly dense dislocation walls were also found at strain ɛ ≥ 0.29. The alloy showed an overall increase in work hardening before fracture, which was ascribed to the occurrence of twins, FCC → HCP phase transformation, microbands, and highly dense dislocation walls.