Microstructure, corrosion and wear performance of plasma electrolytic oxidation coatings formed on Ti–6Al–4V alloy in silicate-hexametaphosphate electrolyte

Coatings have been produced on Ti–6Al–4V alloy by plasma electrolytic oxidation (PEO) using an aqueous solution of Na2SiO3 and (NaPO3)6 with a pulsed electrical regime. The kinetics of coating growth revealed a relatively rapid initial rate, which then slowed significantly as the coating thickened. The coatings were composed of rutile, anatase and amorphous material, and contained relatively large amounts of silicon and phosphorus species. The rutile content increased with extended times of treatment. Corrosion tests showed that the passive current density was lower for short times of PEO treatment, probably due to a smaller number of coating defects. However, in dry sliding wear tests, a long treatment time produced improved durability. The enhanced wear resistance after a prolonged treatment is suggested to be due the modified composition and morphology of the coating.