The tribological performance of ultra-hard ceramic composite coatings obtained through microarc oxidation

A dense ceramic oxide coating approximately 100 μm thick was prepared on a 7075 Al alloy by microarc oxidation in an alkali-silicate electrolytic solution. Coating thickness and surface roughness (Ra) were measured during coating formation. The influence of current density, electrolyte temperature and inter-electrode distance on coating kinetics was investigated. Microstructure and phase compositions were analysed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microhardness of the coating was also measured. The tribological performance of the coatings was evaluated using a dry sand abrasion test, a solid particle erosion test and a pin-on-disc sliding wear test. In addition, the results are compared to detonation-sprayed alumina (Al2O3) coating and bulk Al2O3. The basic mechanism of microarc coating formation is explained. The material removal mechanism during solid particle erosion was investigated, and structure–property correlations were established.