The functionalized graphene/montmorillonite (FG/MTT) nanosheets were synthesized through chemically bonding by a simple, green method, which has remarkable dispersion stability in oil and its lubricating performance was evaluated by a four-ball tribometer. The test results show that FG/MTT has a preeminent lubricant property when the concentration is 0.4 mg/ml. Compared with the bare oil sample, its average friction coefficient (FC) and wear scar diameter (WSD) decrease 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 is discussed and postulated: The FG/MTT with weak interlayer adhesion is filled between the friction pairs to avoid contact and clinging of some asperities, and the sliding between the layers plays a role in lubrication. Furthermore, FG/MTT will 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.
