Understanding of the lubrication mechanism of reduced graphene oxide coating via dual in-situ monitoring of the chemical and topographic structural evolution

Reduced graphene oxide (rGO) has received significant attention as a potential solid lubricant material owing to its superior mechanical and tribological properties. It is considered to be a self-lubricating derivative of graphite because of its low interlayer shear stress. To further understand rGO as a lubricant material, it is necessary to clarify its evolution on the wear track during the sliding process. In this work, a dual in-situ analysis was performed via a tribo-tester instrumented with three-dimensional (3D) laser microscopy and micro-Raman spectrometer. This novel method was employed to investigate the evolutions of tribological, topographical and microstructural characteristics of the rGO coating during the sliding process. The evolution process on the wear track was demonstrated in real time via Raman spectroscopy and 3D confocal profiler. The tribological properties of the rGO coating were affected by the morphology and microstructure of the rGO on the wear track. In addition, the failure mechanism of the rGO coating was attributed to the processes of formation, removal and re-deposition of rGO-based tribofilm. Furthermore, it was determined that variation of morphology and chemical structure of wear track were synchronous in certain sliding stages.