Effects of graphene and MoS2 absorption films on tribological properties of steel-steel contact lubricated by biodiesel

Abstract

ABSTRACT Graphene and molybdenum disulfide (MoS2) have been widely used as lubricating agents to reduce friction and wear in sliding contacts, however, their effects on the tribological properties of steel-steel contact under biodiesel lubrication have been rarely reported. In this study, we prepared steel surfaces with three types of physical coating, namely graphene, MoS2 and a blend of graphene and MoS2, and investigated the tribological properties of these coatings under biodiesel lubrication conditions. Under lubrication of 20 vol% biodiesel, the wear track depth on the disk decreased by 10.3% and 20.5%, while the wear track width on the disk was reduced by 3.4% and 1.7%, respectively, with the graphene and MoS2 absorption layers prepared on the steel disk surfaces. In terms of friction reduction behavior, the MoS2 layer was found to reduce the coefficient of friction (COF) by 2.4%, whereas there was a 2.4% increase in the COF with the graphene layer. Nonetheless, neither the graphene coating nor the MoS2 coating was found to be suitable for the condition of pure biodiesel lubrication, since a significant increase was observed in the wear on both the steel balls and the steel disks with the application of these absorption layers.