Influences of Space Irradiations on the Structure and Properties of MoS₂/DLC Lubricant Film

This work aims at revealing the influences of space irradiations [including the atomic oxygen (AO) and ultraviolet (UV) irradiations] on the MoS₂/DLC solid lubricating film. The changes on microstructure, mechanical and vacuum tribological properties of nanocomposite films after irradiations have been systematically investigated. It is found that the AO irradiation mainly induces the surface oxidation of the film, whereas some oxygen atoms can erode the bulk film along the defects highway; thus, the connectivity of carbon atoms is improved. In contrast, the UV irradiation may break the carbon bonds and functional groups, as well as induce a secondary radical formation, which accelerates the broken and recombination of the carbon chain scission. Specially, the films after irradiations exhibit much higher hardness (>19 GPa), lower friction coefficient (<0.02) and wear rate compared with the original one. The excellent tribological properties of the films after irradiations can be attributed to the synergistic effect of the high sp ³ C content and good crystallization of MoS₂ in the film, which cause the lower carbon and higher MoS₂ content in the wear debris at the contact interface.