Effect of temperature and strain rate on the deformation behaviour and microstructure of Al0.7CoCrFeNi high entropy alloy

The high-temperature deformation behaviour of Al0.7CoCrFeNi alloy was studied at 800-1100 degrees C and 0.01-10 s 1. The alloy exhibited extensive softening via recrystallization and recovery with the examined temperature and strain rate domains. The recrystallization mechanism in the FCC phase was geometric dynamic recrystallization, and that in the BCC/B2 phase was continuous dynamic recrystallization. Further, the BCC/B2 lamellae underwent fragmentation via boundary splitting and termination migration. The amount of softening and subgrain morphology were dependent on the crystallographic orientation of the grains prior to deformation. Apart from lamellar fragmentation, dynamic globularization of BCC/B2 phase was found in certain grain colonies. Compared to heat treatment, hot deformation improved the globularization kinetics. Further, BCC/B2 precipitation occurred along the grain boundaries and at the triple points of the recrystallized FCC phase. However, the overall BCC/B2 phase fraction remained constant. Post-deformed alloy was also characterized by preferential cracking along the allotriomorphic FCC phase boundaries. The difference in strength between the idiomorphic and allotriomorphic regions was attributed to this grain boundary cracking. The activation energy for deformation showed a direct dependency on temperature and strain rate but an inverse relationship with strain.