Transition from defect-dominated strengthening to grain-controlled softening of cold rolled CrCoNi alloy during annealing

The microstructural evolution of medium-entropy alloys (MEAs) at high temperatures deteriorates their mechanical properties, limiting applications in hot-section components. The initial microstructure critically influences this evolution. In this study, CrCoNi alloys were cold-rolled to tailor their initial microstructures and subsequently annealed at different temperatures. Vickers hardness and microstructure were comprehensively characterized to investigate the effect of cold-rolling on microstructural evolution and mechanical behavior. Two distinct temperature-dependent regimes were observed. Annealing below 400 °C promotes defect rearrangement, recovery, and the formation of substructures and interfaces, leading to a hardness increase that deviates from the classical Hall-Petch relationship. Annealing above 400 °C induces progressive recrystallization and grain growth, resulting in a monotonic hardness decrease consistent with the classical Hall-Petch relationship. These findings reveal a transition from defect-dominated hardening to grain-size-controlled softening, providing guidance for optimizing mechanical properties in CrCoNi alloys for high-temperature applications.