Tribological behavior of WS₂-based solid/liquid lubricating systems dominated by the surface properties of WS₂ crystallographic planes

In this paper, WS₂-based solid/liquid systems were established successfully by combining pure WS₂ films with FCPSO (trifluorinated-propyl and chlorinated-phenyl with methyl terminated silicone oil) and SiCH (silahydrocarbons) space oils, and the tribological performances and mechanisms were investigated. The results showed that the tribological properties of the WS₂ film were improved greatly when associated with the SiCH oil, and hence this composite system exhibited a low/stable friction coefficient (<0.08) and a durable wear life (>3 × 10⁶ sliding cycles) both in vacuum and air environments. However, the reverse effect was obtained from the WS₂ film/FCPSO system. The selective adsorption of the WS₂ crystallographic planes with the specific oils seemed to dominate the tribological performance of the composite systems. The SiCH and FCPSO oils have an affinity for the base and edge planes, respectively, of the WS₂ films in their composite systems. The combination of the WS₂ base plane with SiCH was more advantageous for the formation of perfect lubricating and transfer films at the friction contact area, resulting in improved friction and wear performances. This result provides a significant way for us to design solid/liquid lubricating systems based on lamellar solid lubricants.