Morphology and Structure of Al2O3 + Graphene Low-Friction Composite Coatings

Recently, graphene and its derivatives have been of particular interest as a solid lubricant to reduce friction. The aim of this study was to investigate the morphology and structure of low-friction Al2O3 coatings containing reduced graphene oxide (rGO). Using two types of rGO, alumina coatings were produced by the sol–gel dip-coating method and characterized in terms of morphology and structure using SEM and AFM microscopy and Raman spectroscopy. It was found that composite Al2O3 + rGO coatings had diversified morphology depending on the type of graphene used. The dip-coating method used for deposition had a large impact on the morphology and contributed to the orderly arrangement of rGO nanoplates in the coating matrices. It was also shown that there is a correlation between the shape and spatial orientation of nanoplates and the tribological properties of coatings. The structural studies showed differences in the number of graphene defects in the coatings, which may indicate the chemical bonding of graphene with the alumina matrices. These differences may also be responsible for divergences in the tribological properties of the coatings depending on the type of graphene. All our findings indicate the key role of an appropriate balance between the parameters of composite coating production in terms of the desired tribological properties.