The Tribological Properties of the CoCrFeNiMn High-Entropy Alloy Matrix Composites with Solid Lubrication

CoCrFeNiMn HEA-based composites with Cr3C2, 15% Ag, and different mass fractions of CaF2/BaF2 eutectic fluoride were fabricated by spark plasma sintering. The tribological properties and wear mechanism of the composites were investigated from RT to 800 °C. The friction coefficients of CoCrFeNiMn-Cr3C2-Ag-CaF2/BaF2 composites decrease from RT to 800 °C except for 400 °C. At 800 °C, with the increasing mass fraction of the eutectic fluoride, the friction coefficient of the composite decreases from 0.53 to 0.25. The wear rates of the composite with 15% CaF2/BaF2 eutectic fluoride decrease significantly at high temperatures. The CoCrFeNiMn-Cr3C2-Ag-15%CaF2/BaF2 composite exhibits the lowest wear rates at 400 °C, 600 °C, and 800 °C, which are 4.47 × 10−6 mm3/N·m, 5.15 × 10−6 mm3/N·m, and 2.42 × 10−6 mm3/N·m, respectively. At low temperatures, the tribological mechanisms of the composites are micro-plowing and micro-cutting, and Ag is formed as a lubricating film to reduce the friction coefficient. At high temperature, fluorides form a transfer film on the wear scar surface, providing a lubricating effect. Also, the oxide layers and chromate are formed on the worn surfaces of the composites, which are beneficial for improving the wear resistance. Based on the mechanical properties and tribological behavior, the CoCrFeNiMn-Cr3C2-Ag-15%CaF2/BaF2 composite demonstrates the best comprehensive properties.