The Effect of Milling Time and Hot-Pressing on the Structural Properties and Wear Behavior of CoCrFeMnNi High-Entropy Alloys Fabricated by Mechanical Alloying

In this work, CoCrFeMnNi high-entropy alloys (HEAs) were fabricated by mechanical alloying and hot-pressing-assisted powder metallurgy method. For HEA powders, the effect of milling time on the morphology, particle size, crystallite structure and oxidation resistance of the HEA particles was studied. For sintered HEAs, effects of milling time and hot-pressing on the microstructure evolution, density, hardness, friction coefficient, wear rate and surface roughness of CoCrFeMnNi HEAs were investigated. Milling the particles for 5 h resulted in further cold welding of the initial particles and the formation of many coarse and cold-welded particles. The particle-size distribution obtained after 5 h of milling was single peaked and had a relatively narrow distribution range. An increase in oxidation resistance with increasing milling time was observed due to the embedding of hard and highly oxidation-resistant particles such as Co, Cr and Ni into ductile Fe particles. The CoCrFeMnNi alloy produced with 5 h of milling and at 650 MPa pressure had the highest relative density with 86.29%, while the sample fabricated with 0.5 h of milling and 550 MPa pressure showed the lowest relative density with 77.34%. The lowest wear rate was obtained in the sample produced with 5 h of milling and at 650 MPa. At the same time, the lowest average coefficient of friction was obtained as approximately 0.28 for the sample produced under these conditions.