Microstructure evolution and deformation mechanism of coherent L1₂-strengthened high-entropy alloy during sliding wear

Face-centered-cubic high-entropy alloys (HEAs) strengthened with coherent ordered nanoprecipitates have demonstrated excellent strength-ductility synergy, even at elevated temperature. However, there still lacks fundamental understanding on their microstructure evolution and deformation mechanisms during dry sliding wear. Herein, we systematically investigated the friction and wear behaviors of CoCrNi₂(Al_0.2Nb_0.2) alloy with high-density coherent L1₂ nanoprecipitates during sliding at room and elevated temperatures, with particular focus on wear-induced microstructure evolution. The alloy shows a low wear rate of 1.80 × 10⁻⁵ mm³/(N⋅m) at room temperature (RT) and even an ultralow wear rate of the order of 10⁻⁶ mm³/(N⋅m) at 600 °C. Detailed TEM analyses reveal that sliding-induced stacking faults (SFs) and dislocation cells play important roles in the formation of the gradient microstructure at RT and 600 °C, respectively. The superior wear resistance at RT is mainly attributed to the precipitation strengthening of high-density coherent L1₂ phase and the dynamic work-hardening of SF networks near the sliding surface. However, at 600 °C, the reduced wear rates and coefficients of friction are associated with the formation of glaze layer and the high resistance to thermal softening. This work provides significant insight into the sliding-induced microstructure evolution and deformation mechanism of L1₂-strengthened high-entropy alloys during sliding wear.