Effects of Cold Rolling and Annealing Treatment on Microstructure and Properties of CoFeNiMnV High-Entropy Alloys

Herein, 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 deposited CoFeNiMnV HEAs exhibit a face-centered cubic (FCC) structure with a small amount of sigma phase precipitation. After 50% CR, the microstructure of CoFeNiMnV HEAs is severely deformed along the rolling direction, and the grain size is obviously refined. Therefore, the hardness and strength of the alloy are significantly improved. The rolled CoFeNiMnV HEAs are annealed at 500, 700 and 900 degrees C, for 60 min. The results show that annealing at 500 degrees C has little effect on the microstructure and dislocation density of the alloy, and the alloy still maintains high strength and hardness. With increasing of annealing temperature to 700 and 900 degrees C, the dislocation density of the CoFeNiMnV HEAs is significantly reduced. Meanwhile the sigma phase is gradually dissolved, and the recrystallized grains and annealing twins are significantly coarsened. The analysis suggests that it decreases the strength of the CoFeNiMnV HEAs, but increases the elongation. CoFeNiMnV HEAs annealed at 700 degrees C for 60 min after CR exhibit an excellent high strength-toughness combination.

Automated summary

In this study, the evolution of microstructure and mechanical properties of CoFeNiMnV high-entropy alloys (HEAs) fabricated by powder plasma arc additive manufacturing (PPA-AM) was investigated using a combination of cold rolling and annealing treatment. Cold rolling significantly refined the grain size and improved the hardness and strength of the alloy. Annealing treatment at different temperatures resulted in reduced dislocation density, dissolution of sigma phase, and coarsening of recrystallized grains and annealing twins. CoFeNiMnV HEAs annealed at 700 degrees C for 60 min after cold rolling exhibited an excellent high strength-toughness combination.