Effects of mechanical milling on microstructure and tensile properties of CoCrFeMnNi high-entropy alloys produced by spark plasma sintering

CoCrFeMnNi high-entropy alloys with nearly full density were fabricated by spark plasma sintering (SPS) process. The effects of mechanical milling on the microstructure and tensile properties of the CoCrFeMnNi alloys were investigated. The results show that the sphericity of the pre-alloyed powders decreases with the milling time increasing. The phase composition of as-SPSed alloys presents a single face-centered cubic structure, and the grain size decreases with the increase of ball-to-powder weight ratio and mechanical milling time. Compared with the alloys without mechanical milling, the yield strength of the as-SPSed alloys increases with the increase of mechanical milling energy, which reaches the highest value when the ball-to-powder weight ratio is 7.5:1.0 and the mechanical milling time is 100 h, increasing by about 19%, which is mainly due to the fine grain strengthening. The ultimate tensile strength tends to firstly increase and then decrease, which reaches the highest value when the ball-to-powder weight ratio is 7.5:1.0 and the mechanical milling time is 30 h, increasing by about 12%.