Reduced friction and wear of electro-brush plated nickel composite coatings reinforced by graphene oxide

The nano-scale studies in the literature have revealed the excellent anti-friction properties of graphene and its great potential as a nano solid lubricant. However, for macro-scale applications the integrity and durability are main problems for most graphene-based surface coatings. One way to mediate the durability issue while exploiting the tribology of graphene is graphene-based composites. In this work, nickel-graphene oxide (GO) composite coatings were fabricated on steel by electro-brush plating. The effects of GO on the tribological properties were investigated. The results show that the composite coatings possess much lower friction than GO-free nickel coating (up to 47% less against a bearing steel ball, and 30% less against an alumina ball). As the GO load increases from 0 to 4 mg/ml, the wear rate of the resulting composite can be reduced significantly by approximately 90%. Detailed post-test studies of the wear tracks and the counterpart were conducted using SEM, EDS, Raman and FIB/SEM. The improved tribological properties can be attributed to the strengthening effect, the retention of oxide tribo-films and the formation of GO rolls during sliding. The tribological behaviour of the Ni-GO nano-composite coating and a Ni-graphite composite coating was compared, and their different wear mechanisms have been discussed.