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(Al0.2Nb0.2) alloy with high-density coherent L1(2) 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 x 10(-5) mm(3)/(N center dot m) at room temperature (RT) and even an ultralow wear rate of the order of 10(-6) mm(3)/(N center dot m) at 600 degrees 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 degrees C, respectively. The superior wear resistance at RT is mainly attributed to the precipitation strengthening of high-density coherent L1(2) phase and the dynamic workhardening of SF networks near the sliding surface. However, at 600 degrees 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 L1(2)-strengthened high-entropy alloys during sliding wear.

Automated summary

In this study, the friction and wear behaviors of CoCrNi2(Al0.2Nb0.2) alloy with high-density coherent L1(2) nanoprecipitates during sliding at room and elevated temperatures were systematically investigated. The results showed that the alloy exhibited low wear rate and excellent wear resistance at room temperature, attributed to the precipitation strengthening and dynamic workhardening. At elevated temperature, the reduced wear rates and coefficients of friction were associated with the formation of glaze layer and high resistance to thermal softening. This work provides significant insight into the sliding-induced microstructure evolution and deformation mechanism of L1(2)-strengthened high-entropy alloys during sliding wear.