Structure design of Al2O3/TiC/CaF2 multicomponent gradient self-lubricating ceramic composite and its tribological behaviors

To overcome the conflict between the tribological and mechanical properties of traditional self-lubricating ceramic composites, an Al2O3/TiC/CaF2 multicomponent gradient self-lubricating ceramic composite was structurally designed by using a compositional gradient model for multicomponent functionally gradient materials. According to the model, the Al2O3/TiC/CaF2 gradient composite was gradient-controlled using two gradient indexes n(1) and n(2), and was accordingly categorized into four types with different gradient systems. A proper gradient system was selected by calculating the distribution of residual thermal stresses via an analytical method and the finite element method. The as-prepared AAl(2)O(3)/TiC/CaF2 gradient composite was characterized by reducing the distribution of CaF2 solid lubricants from its surface layers to its middle layer and the residual compressive stresses existing in the surface layers. The measurement obtained using the indentation crack method showed that both the surface layers and middle layer were subjected to residual compressive stresses. Compared with the homogeneous composite, the flexural strength, Vickers hardness, and fracture toughness of the gradient composite increased by 21%, 16%, and 5.9%, respectively. The results of the dry sliding friction test demonstrated that the gradient composite had comparable antifriction property and superior wear resistance to the homogeneous composite.