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

Powder metallurgy can produce high-performance high-entropy alloys with fine and homogenous microstructure. In the present work, CoCrFeMnNi high-entropy alloys with nearly full density were fabricated by spark plasma sintering (SPS) process. The effects of mechanical milling of pre-alloyed powder on microstructure and tensile properties of CoCrFeMnNi powder compacts were investigated. The results showed that the sphericity of the pre-alloyed powder decreases with the increasing milling time. The phase composition of as-SPSed alloy presents a single FCC structure, and the grain size decreases with the increasing pellet ratio and mechanical milling time. Compared with the power compact without mechanical milling, the yield strength of the as-SPSed alloy increases with the increasing mechanical milling energy, which reaches the highest value when the pellet ratio is 7.5:1 and the mechanical milling time is 100 h. increasing by about 19%. The increment of yield strength (about 19%) 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 pellet ratio is 7.5:1 and the mechanical milling time is 30 h, increasing by about 12%.