High temperature friction and wear properties of graphene oxide/polytetrafluoroethylene composite coatings deposited on stainless steel

Polytetrafluoroethylene (PTFE) coating is known as a low friction material that is often used as a solid lubricant coating. However, due to its relatively weak mechanical strength, wear has been a critical issue which needs to be overcome. In the present work, a composite coating composed of PTFE and graphene oxide (GO) was investigated with the aim to significantly improve the wear resistance of PTFE, in both room and elevated temperature conditions. PTFE/GO (PG) composite coatings with varying amounts of GO in the PTFE matrix were successfully deposited on stainless steel (SS) substrates by the spin coating method. Both micro- and macro-scale tests were performed in order to assess the tribological properties of the coatings under a wide range of normal load. Results of the micro-scale tests showed that the coefficient of friction and the wear rate could be remarkably reduced to 0.1 and 0.65 × 10^-9 mm³ N^-1 m^-1, respectively, with inclusion of 15 vol% of GO in the PTFE matrix. This coating also demonstrated low friction and wear properties up to 400 °C in the macro-scale tests. The superior tribological properties of the PG coating were attributed to the synergistic effects of PTFE and GO. Specifically, the existence of a rather homogeneous dispersion of high strength GO in the low friction PTFE matrix allowed for generation of a self-lubricating film along the wear track.