On the Tribological Properties of RGO–MoS2 Composites Surface Modified by Oleic Acid

To study the effect of oleic acid surface modified RGO/MoS2 composite lubricating additives on the friction and wear properties of 10# White Oil (10# WO). The influences of different concentrations of reduction graphene oxide/molybdenum disulfide (RGO–MoS2) and oleic acid surface modified reduction graphene oxide/molybdenum disulfide (OA-RGO–MoS2) on the lubricating properties in 10# WO was investigated using a four-ball long-term friction and wear tester. The microscopic morphology, lattice structure, composition and element valence of the prepared material were characterized by scanning electron microscope, Raman spectroscopy, Infrared Spectroscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, element analyzer and other instruments. The diameter, structure, morphology, composition and element valence state of the wear scar were obtained by multifunctional universal tool microscope, scanning electron microscope and X-ray photoelectron spectroscopy. In the RGO–MoS2 white oil system, when 0.4 wt% RGO–MoS2 is added, the anti-friction effect is the best, and the average friction coefficient (AFC) reduced by 21.8%. When 0.2 wt% RGO–MoS2 is added, the anti-wear effect is the optimal, and the average wear scar diameter (AWSD) decreased by 12.4%. In the OA-RGO–MoS2 white oil system, when 0.2 wt% OA-RGO–MoS2 is added, the anti-friction and anti-wear effects are the best, and the AFC reduced by 33.3%, and AWSD reduced by 14.1%. Compared with RGO–MoS2, OA-RGO–MoS2 has a higher degree of graphitization, larger interlayer spacing, lower degree of layered accumulation, higher MoS2 load, and weaker thermal stability. Both lubricating additives have good anti-friction and anti-wear effects at low concentrations, and the anti-friction and anti-wear effects are more prominent after being modified by oleic acid. Analysis of friction mechanism shows that a lubricating protective film containing iron, oxygen, molybdenum, carbon, and sulfur is formed through adsorption or tribochemical reaction during the friction process, which improves the lubrication state and plays a role in reducing friction and anti-wear.