Tribo-induced microstructural changes and associated wear mechanisms of CoFeNi2 medium entropy alloy at elevated temperatures

This work presents an experimental investigation into the tribological behavior of CoFeNi2 medium entropy alloy (MEA) across a broad temperature spectrum. Experimental findings reveal that the coefficient of friction (COF) keeps climbing from 400 °C to 800 °C. Concurrently, the specific wear rate initially increases from 400 °C to 600 °C but subsequently declines at 800 °C. Microstructure analysis discloses that the formation of a flat protective layer, coupled with the subsurface layer comprised of ultrafine grains, culminates in a minimum COF at 400 °C. At higher temperatures, the synergistic effect of oxidation and stress/strain promotes the thickening of protective tribo-layer and the emergence of a gradient structure in the dynamic recrystallization layer, thereby reducing wear rate at 800 °C.