Modelling of a thin soft layer on a self-lubricating ceramic composite

Friction and wear of a self-lubricating ceramic composite under unlubricated sliding contact conditions is dependent on the formation and regeneration of a thin soft surface layer. Experimental observations have shown that a thin soft layer (third body) may be formed depending on the tribological tests conditions. This thin soft layer is a pre-requirement for the occurrence of low friction in the mild wear regime. This paper proposes a physically based model for the process of the formation and removal of the soft layer. The model is developed on the basis of mechanical stresses in the soft second phase and the elastic-plastic contact between a rough surface and a flat surface. Based on the model, the thickness of the soft surface layer on a ceramic substrate is predicted. The results show that the thickness of the soft layer is mainly determined by the mechanical properties of soft phase as well as the applied load.