Metastability-driven room temperature strain hardening in a nitrogen added FeMnCoCrN high-entropy alloy

This study deals with the strain hardening capability of a nitrogen added FeMnCoCr high-entropy alloy during room temperature tensile deformation with an emphasize on the mechanical stability of FCC phase. The heightened metastability of the FCC phase provides a proper condition for hierarchical evolution of dual-phase FCC-HCP structure which finally promotes the formation of 63 % HCP martensite. Initially favoring slip mechanisms, the texture of the FCC phase transitions to geometrically hard orientations, thereby reducing its deformation accommodation capacity. This transition prompts the involvement of the HCP phase, initially evidenced by the emergence of new FCC phase and ε-twins at HCP martensite intersections. Subsequently, the formation of thickened ε-twins within the primary HCP lathes further contributes to deformation accommodation, explaining the observed excellent hardening behavior in the as-cast structure.