Synergy Effect of Metal Surface Texture on the Low Friction of Graphene-Oxide Dispersed Oil

The low-friction mechanism of graphene oxide-dispersed lubricants remains to be elucidated. In this study, pin-on-disk friction tests were conducted on specimens with various surface properties to clarify the effect of the lubrication condition of the contact point on the low-friction by dispersing graphene oxide (GO) particles into lubricating oil. The relationship between the lubrication state and the friction coefficient was investigated using Λ ratio calculated from the surface roughness of the sliding area after the test and the calculated minimum oil film thickness. The friction coefficient decreased as Λ ratio increased, that is, as the lubrication state approached fluid lubrication. For the disk specimen containing pit shapes on the surface, the friction coefficient was significantly reduced by up to 70% for the graphene oxide-dispersed lubricant compared to the base oil alone. On the other hand, the friction reduction was only 20% for the specimen without pits. The composite surface roughness of the sliding area after the test was significantly improved for the disk with pits, which indicates that the progress of running-in process during the test affects the friction properties of the GO containing lubricant.