Microarc oxidation and spraying graphite duplex coating formed on titanium alloy for antifriction purpose

Microarc oxidation coatings were fabricated on Ti6Al4V alloy in NaAlO2 containing solution. Microstructure and adhesion properties of the coatings were evaluated. For antifriction purpose, a novel duplex coating of microarc oxidation combined with spraying graphite process was developed. The results show that the microarc oxidation coating with 20 μm thickness is compact and uniform in the inner layer, while porous in the surface layer. The coating has high adhesion strength of about 110 MPa to the substrate. The novel duplex coating exhibits good antifriction property, registering friction coefficient of ≈0.12, which is 5 times lower than that of the 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 underlying loading layer and the graphite layer on top of it working as solid lubricant.