Influence of Al and Mo on microstructure and tribological behaviors of Co-based superalloy

In this study, three Co-based superalloys with different Al and Mo concentrations were prepared by powder metallurgy (PM) method to investigate their influences on the microstructure and tribological properties. Replacing Al with Mo in the alloy has been found to decrease its hardness and yield strength, but increases its compressive ductility at room temperature. With the increase of Mo content, the formation of the HCP phase from the original FCC solid solution phase was promoted, and the microstructure of the alloy became relatively coarse. All superalloys showed decreased friction coefficient during sliding wear at 800 ◦C. The alloy with the highest content of Mo and lowest content of Al exhibited the greatest wear resistance at both room temperature and 800 ◦C. Formation of a continuous compact glaze layer rich in Cr2O3 and CoMoO4 oxides results into a significant reduction in both friction coefficient and specific wear resistance, and the synergistic effect of high temperature wear-induced oxides is the dominant contribution rather than the transformation of HCP from the original FCC solid solution phase at high temperature.