Wear behavior of CoCrFeNi high-entropy alloy prepared by mechanical alloying

Equiatomic quaternary CoCrFeNi powder was prepared from the individual metals by mechanical alloying of the mixed powders at room temperature. The as-milled powder contained particles of irregular shape with an average particle size of 0.62 μm, and exhibited a dual-phase composition of the face-centered cubic and the body-centered cubic structures. The as-milled powder was consolidated by hydraulic pressing at room temperature and sintered at 950 °C in argon and vacuum. The compacted material exhibited a single-phase composition of the face-centered cubic structure alone and a chemical composition close to equiatomic with uniform distribution of all constituents, indicating that the desired CoCrFeNi high-entropy alloy (HEA) had been formed. The microhardness of the vacuum-sintered CoCrFeNi HEA was measured to be 118±7 HV, exceeding that calculated by the rule of mixture. The coefficient of friction was determined by pin-on-disk dry sliding studies at room temperature and found to be 0.65 and 0.44 for the applied loads of 25 for 35 N, respectively, and the corresponding wear rates were 4.6×10−4 and 9.1×10−4 mm3/N·m. XPS studies on the worn alloy surfaces showed the formation of oxidized tribo-layers, composed of predominantly Cr2O3. Overall, this study has demonstrated that mechanical alloying followed by simple furnace sintering at a moderate temperature is able to yield an abrasion-resistant CoCrFeNi HEA suitable for structural applications.