Role of recrystallization and second phases on mechanical properties of a (CoCrFeMnNi)95.2Al3.2Ti1.6 high entropy alloy

Abstract

The present work reports microstructures and mechanical properties of the homogenized and cold-rolled (CoCrFeMnNi)95.2Al3.2Ti1.6 (at. %) high entropy alloy annealed at various temperatures. The material was cold-rolled and annealed in the temperature range from 600 ?C to 1000 ?C for 1 h. The ? phase was observed in the annealing temperature range from 600 ?C to 800 ?C while the B2 phase was observed in the annealing temperature range from 700 ?C to 900 ?C. The fully recrystallized material annealed at 900 ?C shows a considerably lower grain size compared to the reported grain size of the CoCrFeMnNi alloy, due to the presence of second phase particles. With increasing annealing temperature, a fraction of fully-recrystallized grains increases, leading to an increase in ductility and a decrease in strength. The material annealed at 900 ?C and 1000 ?C shows a low strength but large ductility due to fully recrystallized microstructures. Grain size strengthening and precipitation strengthening by B2 particles play a major role in the yield strength of the fullyrecrystallized material annealed at 900 ?C. The deformation mechanism of the material annealed at 900 ?C is mainly dislocation slip with the minor occurrence of deformation twinning. A high density of dislocations near the B2/FCC matrix suggests the strengthening effect of the B2 phase. The material annealed at 800 ?C shows ultimate tensile strength exceeding 1 GPa due to the combined effect of partially recrystallized microstructure and precipitation hardening and shows moderate ductility due to the less brittle character of the B2 phase by Ti alloying.