Strengthening mechanism of CrCoNi medium-entropy alloy from the partially recrystallized structure to the fully recrystallized heterogeneous structure

Abstract

Vast amounts of strengthening methods towards the single phase face-centered cubic CrCoNi medium-entropy alloy have been carried out in recent years. In this study, a partially recrystallized structure, as well as the fully recrystallized heterogeneous structure, were introduced in CrCoNi medium-entropy alloy through cold-rolling and subsequent annealing that purposely deployed under gradient temperatures. The annealed specimens were subjected to tensile tests, from which detailed parameters of the mechanical properties were derived. Strengthening from grain boundaries, dislocations, solid solutions are quantified, suggesting the existence of other strengthening mechanisms. We attribute the increased strength to the appearance of extensive shear bands, nanograins, nanotwins, HCP lamellas. In addition, the dual-heterogenous structure is believed to contribute to similar ultimate tensile strengths among the annealed specimens. More importantly, dislocations, stacking faults, twins appeared in this alloy as the deformation modes, contribute to the extraordinary fracture elongation.