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

The present work reports microstructures and mechanical properties of the homogenized and cold-rolled (CoCrFeMnNi)_95.2Al_3.2Ti_1.6 (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 σ 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 fully-recrystallized 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.