Effects of Cold Rolling and Annealing Treatment on Microstructure and Properties of Cofenimnv High-Entropy Alloy

In this study, a combination of cold rolling (CR) and annealing treatment is used to investigate the evolution of the microstructure and mechanical properties of CoFeNiMnV high-entropy alloys (HEAs) fabricated by powder plasma arc additive manufacturing (PPA-AM). The as-deposited CoFeNiMnV HEAs exhibit a single-phase face-centered cubic (FCC) structure with a small amount of accompanying V-Mn-rich precipitates. After 50% cold rolling, the microstructure of CoFeNiMnV HEAs is severely deformed along the rolling direction, which the crystal structure is obviously refined, and the hardness and strength of the alloy are significantly improved (compared to the PPA-AM deposited sample, the hardness is about 1.9 times higher and the tensile strength is about 1.4 times higher). The rolled CoFeNiMnV HEAs is annealed at 500 °C, 700 °C and 900 °C, respectively, for 60 min. The results show that annealing at 500°C has little effect on the microstructure and dislocation density of the alloy, and the alloy still maintains high strength and hardness. After annealing at 700 °C and 900 °C, the combined effects of the significantly decrease dislocation density, the gradual dissolution of V-Mn precipitates, obviously coarsened recrystallization grains, and significant coarsening of annealing twin size decreased with the annealing temperature decrease the strength of the alloy, but the elongation improved significantly. CoFeNiMnV HEAs annealed at 700 °C after cold rolling exhibit an excellent high strength-toughness combination.