Twin-mediated microstructural stability and grain-growth stagnation in FeMnCoCrN high-entropy alloy

Abstract

The microstructural and mechanical evolution of a FeMnCoCrN high-entropy alloy subjected to cold rolling followed by isothermal annealing at 900°C was systematically investigated. The homogenized alloy exhibited a single-phase FCC structure with coarse equiaxed grains and a high density of annealing twins, consistent with its low stacking-fault energy. Cold rolling introduced severe lattice distortion and deformation substructures, providing sufficient stored energy for rapid recrystallization. Full recrystallization occurred during the early stage of annealing, followed by normal grain coarsening. With further annealing, grain growth entered a stagnation regime in which the average grain size remained nearly unchanged despite chemical homogeneity. Kinetic analysis and compositional mapping suggest that classical solute- or particle-drag mechanisms are unlikely to dominate this behavior. Instead, the stagnation coincided with the progressive formation of coherent Σ3 annealing twins, which may reduce boundary mobility by replacing high-energy interfaces with low-energy segments. This microstructural state was associated with a favorable strength–ductility balance. Upon prolonged annealing, normal grain growth resumed as the twin network coarsened. These results suggest that twin-mediated grain-boundary evolution plays an important role in controlling thermal stability and mechanical performance in this low-stacking-fault-energy interstitial high-entropy alloy.