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

Abstract

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 (R_a) 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.