Novel DLC/ionic liquid/graphene nanocomposite coatings towards high-vacuum related space applications

It is currently a challenge for space tribology to develop a long lifetime and high bearing capacity lubricant meeting the requirements of space applications. Herein, we dispersed graphene into ionic liquid, prepared novel composite coatings of diamond-like carbon (DLC)/ionic liquid (IL)/graphene with different graphene concentrations, and investigated its space performance under high vacuum and space radiation conditions. IL/graphene nanofluids with different concentrations were examined by Fourier transform infrared spectroscopy (FTIR). Furthermore, IL/graphene nanofluids after friction tests were investigated by X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The results showed that the graphene concentration would obviously affect the spatial tribology performance of the composite coatings. Because the excess graphene in the IL would tend to form irreversible agglomerates, leading to reduction of the effective graphene dose, an optimum graphene concentration (0.075 mg ml(-1)) in IL for the composite coatings was required to exhibit the lowest friction coefficient, the highest bearing capacity and the strongest anti-irradiation in a simulated space environment. In addition, XPS spectra further confirmed that the formation of a fluorinated oil-containing carbon-rich tribofilm between the friction pairs further ensured the good antifriction and wear resistance performance of DLC/IL/graphene.