An investigation on the tribological properties of graphene and ZDDP as additives in PAO4 oil

The prime objective of this study was to extend the application of graphene additive in oil solution via investigating the frictional interaction of graphene and ZDDP composite additives in point contact lubrication. Accordingly, 0.05 wt% graphene, 1 wt% ZDDP and their mixtures as additives were added into PAO4 base oil. The ball-on-disk reciprocating experiments were carried out under the load of 30 N, 80 N, 155 N and 310 N. The tribological performance of the single system containing graphene and ZDDP were evaluated separately to compare the tribological property of the composite system containing graphene + ZDDP. The result revealed that the friction coefficient of the graphene/ZDDP composite system was slightly higher compared to PAO4 oil under high load. Whereas the composite system exhibited excellent wear resistance under all loads, reducing the wear rate by 77% in comparison to that of PAO4 oil under a load of 30 N. The reduction in wear is attributed to the formation of the graphene tribofilm and the protective polyphosphate film, which avoided the direct contact with the sliding surface and effectively inhibited the wear of steel materials.