Microstructure and tribological properties of self-lubricant gradient Ti(C, N)-based cermets

In the present work, Ti(C, N)-based cermets with self-lubricant gradient layer were prepared via vacuum liquid sintering and subsequent solid carburization. The sliding wear test was carried out using block-on-ring equipment. The microstructure and elements distribution of the gradient layer and the effect of gradient layer on the mechanical properties as well as tribological properties were investigated in this paper. The results indicate that a layer enriched in graphite phase but deficient in Ni binder phase is achieved by carburization. Furthermore, the thickness of graphite-rich layer as well as Ni-poor layer increases as the carburizing time prolongs. The hardness of the cermets was obviously different along the depth direction which is caused by the gradient distribution of graphite, carbonitrides and binder phase. In addition, the cermets with gradient layer show better tribological properties than the ones without gradient layer, since the graphite phase introduced by carburization forms a tribofilm during friction. The tribofilm protects the surface from the hard abrasive particles ploughing and reduces the possibility of the formation of grooves, which improves the tribological properties obviously. The cermets carburized for 30mins show the best tribological properties due to the existence of gradient layer with appropriate volume of graphite.