Tribological characterisation of epoxy–graphene–liquid filler composite coatings on steel under base oil external lubrication

In our earlier study, epoxy-based composites with graphene (10 wt-%) and in situ liquid fillers (base oil SN150 or perfluoropolyether at 10 wt-%) were found to provide low friction and highly wear durable as thin coatings on the steel substrate in dry interfacial state. In this present work, we have tested this composite in the presence of an external lubricant (base oil SN150). The lowest coefficient of friction was recorded as 0.04 and the lowest specific wear rate was measured as 9.8 × 10⁻⁷ mm³Nm⁻¹ for the composites without any failure of the coating up to 200,000 sliding cycles. It is shown that such polymeric coatings can be an excellent boundary film in both dry and lubricated conditions for various bearings.