Lubrication Performance of Graphene-containing Oil on Steel and DLC-coated Surfaces
Several studies have successfully demonstrated the friction-reduction and anti-wear properties of graphene on the nano- and micro-scales, but our understanding of the tribological behaviour of graphene on the macro-scale remains very limited. Accordingly, this study presents the macro-tribological behaviour of a graphene-containing oil in the lubrication of steel/steel contacts and DLC/DLC contacts. We show that graphene platelets, as additives to the base oil, can, especially in the boundary-lubrication regime, decrease the friction in the DLC/DLC contacts by up to 50%, as well as in the steel/steel contacts by up to 44%. The predominant lubrication mechanism of the graphene platelets was shown to be the formation of a protective tribofilm for both types of surfaces. The effects of the concentration of graphene (0–5 wt.%) and the lubrication regimes on the formation of the tribofilm are also investigated and explained with a schematic 2-D contact model.