Tribological behavior of microarc oxidation coatings formed on titanium alloys against steel in dry and solid lubrication sliding

The coatings mainly composed of nanostructured TiO2 were deposited on Ti6Al4V alloy by microarc oxidation (MAO). The duplex coatings of microarc oxidation combined with spraying graphite process were fabricated for the antifriction purpose. The tribological properties of unpolished, polished and duplex coating against steel under dry friction conditions were examined. It is found that antifriction property of the polished microarc oxidation coating is superior to that of the unpolished one. The improvement is attributed to the low surface roughness and the nanocrystalline structure of coatings. The duplex coating exhibits best antifriction property, registering a lower and steady friction coefficient of ≈0.12 than that of the polished microarc oxidation coating sliding in the similar condition. The good tribological property is attributed to the specially designed duplex structure, the coating adhering strongly to the substrate and serving as the load-supporting underlayer and the graphite layer on top of it working as solid lubricant.