Effect of cobalt content on high-temperature tribological properties of TiC-Co coatings

Titanium carbide based cermets are promising wear resistant coating materials used at elevated temperatures in hostile environment owing to their excellent mechanical, physical and chemical properties. In this work, TiC-Co composite coatings with different Co content, as well as a WC-17Co reference coating are prepared by plasma spraying and their wear resistances are investigated. The friction coefficients and wear rates tested by dry sliding friction at 600 degrees C are used to characterize the high-temperature wear resistance of the coatings. The phase and microstructure evolution of the coatings before and after friction test are evaluated to conclude the wear mechanisms of these coatings. The results show that as-prepared TiC-Co composite coatings are composed of TiC, Ti, alpha-Co, r-TiO2 and CoO phases and Ti oxidizes to r-TiO2 phase during friction test, which is resulted from decarburization and oxidation of TiC. Among all the coatings, TiC-15Co has the minimum friction coefficient and lowest wear rate. It is contributed to the balanced ratio and good bonding between Co-rich soft phases and Ti-rich hard phases. The wear mechanisms of TiC-Co composite coatings are abrasive wear for low Co content (<15 wt%) coatings and adhesion/fatigue wear for high Co content ones.