Effect of normal load on the tribological behavior of graphene coating under current-carrying state

The feasibility of graphene coating (GC) in enhancing the tribological performances of sliding electrical contact system (SECS) is studied, and the friction and wear characteristics of GC under different normal loads is explored. Results show that compared with bare brass surface, the presence of GC can reduce the friction coefficient by about 76.9 %. Additionally, the wear depth of the GC surface is too low to detect, while the wear depth of the bare brass surface reaches about 10 µm, suggesting that GC can effectively improve the interface wear. For the GC surface with the normal load varies from 1 N to 6 N, the larger normal load is beneficial for reducing the friction coefficient. Especially when the normal load is 6 N, the friction coefficient continues to remain at about 0.1, and the degree of change is quite small. However, a larger normal load may trigger the friction-induced vibration (FIV) generation. No direct relationship between the friction coefficient and the FIV can be summarized in this state. The variation degree of contact resistance first lowers and then increases as the normal load increases. Thereby, the GC may operate well in lowering friction, vibration, and resistance variations in current-carrying state with the aid of a suitable normal load. Wear morphological analysis showed that when the normal load increases from 1 N to 6 N, the GC coating would suffer more serious damage and a large number of graphene fragments would be formed. These graphene fragments remaining in the worn areas still provide good lubrication and reduce friction.