Dependence of Friction and Wear on the Microstructures of WS₂ Films under a Simulated Space Environment

Atomic oxygen (AO) has an important influence on the performance of solid lubricating materials applied in space. The tribological behaviors of both sputtered WS2 films without and with a dense layer were mainly investigated under the ex situ AO irradiation condition. AO irradiation results in the worse tribological property for the WS2 film without a dense layer. On the contrary, it is surprising that the WS2 film with the dense layer exhibits a lower friction coefficient after irradiation, which is different from the reported results that the solid lubricating films always increased the friction and wear because the surfaces of the films were oxidized by AO. Meanwhile, it is found that the generated W oxides contributes to the partial surface of the wear track becoming smooth because of the shear and slip of crystal planes for WS2 crystals on the surface of the dense layer. Eventually, the lubricating mechanisms of the irradiated WS2 films are also revealed via correlating the friction and wear characteristics of the films.