Tribological Properties of the Functionalized Graphene/Montmorillonite Nanosheets as a Lubricant Additive

The functionalized graphene/montmorillonite (FG/MTT) nanosheet was synthesized through chemical bonding by a simple, green method, which had remarkable dispersion stability in oil and its lubricating performance was evaluated by a four-ball tribometer. The test results showed that FG/MTT had a preeminent lubricant property when the concentration was 0.4 mg/ml. Compared with the bare oil sample, its average friction coefficient (FC) and wear scar diameter (WSD) decreased by 50.4% and 13.2%, respectively. The synergistic effect between FG and MTT was further explored by comparing the lubricant mechanism of the different additives. After synthetically analyzing worn surface by means of scanning electron microscopy and X-ray photoelectron spectroscopy, the lubrication mechanism of the FG/MTT nanocomposite as oil additive was discussed and postulated: the FG/MTT with weak interlayer adhesion was filled between the friction pairs to avoid contact and clinging of some asperities, and the sliding between the layers played a role in lubrication. Furthermore, FG/MTT would react with the surface of the friction pair to form a repair layer composed of Fe2O3, SiC, SiO2, and aluminosilicate, mending the grinding surface and promoting the hardness after friction.