Wear mechanism transitions in FeCoNi and CrCoNi medium-entropy alloys from room temperature to 1000 °C

• The hardness, wear rates and characterizations at 1000 °C are new records for MEAs. • The roles of Fe and Cr and their oxides in wear are discussed. • A new wear transition mechanism is revealed with deformable glaze layer. Many machine components are operated in dry sliding, elevated temperature, and oxidizing environments, leading to material failure or loss of functionality. Despite previous wear studies on conventional alloys, wear-related properties in high-entropy alloys (HEAs) and medium-entropy alloys (MEAs) up to 1000 °C are rarely reported. Here we systematically study the high-temperature hardness, wear behaviours and mechanisms of two popular MEAs, FeCoNi and CrCoNi, from room temperature to 1000 °C. We find that the wear resistance of FeCoNi surpasses that of CrCoNi at room temperature, 600 °C, and 800 °C. Contrarily, the wear resistance of CrCoNi surpasses that of FeCoNi at 400 °C and 1000 °C. By characterizing wear tracks, we identify that these wear-mechanism transitions are associated with alloy elements, oxidation rates, and oxide types. At room temperature, FeCoNi forms a spinel oxide layer with a lower wear rate than CrCoNi. At 400 °C, the wear rates of FeCoNi and CrCoNi are comparable because of temperature softening. At 600 °C and 800 °C, FeCoNi shows Co 3 O 4 as the main constituent of the glaze layer, enhancing wear resistance compared to CrCoNi. At 1000 °C, such glaze layer in FeCoNi undergoes severe plastic deformation, reducing its wear resistance; the Cr 2 O 3 oxide layer formed in CrCoNi remains hard and less deformable, contributing to its higher wear resistance. This study provides a fundamental understanding of the effect of principal elements on the wear performance in FeCoNi and CrCoNi-related MEAs and HEAs.