High efficient co-doping in plasma electrolytic oxidation to obtain long-term self-lubrication on Ti6Al4V

Titanium alloys are important aerospace metals but suffer the poor mechanical property in high-loading area. Plasma electrolytic oxidation can improve their hardness and reduce friction but the precursor competition of functional phases in PEO electrolyte is inevitable. This work provides a new strategy to avoid ions competition and precipitation by choosing anionic salt (K2ZrF6) and cationic salt (Ce(Ac)3) as the precursors of the hard phase (ZrO2) and lubrication phase (monoclinic CePO4), respectively. As a result, the ions competition is avoided to achieve simultaneous high-content doping of functional phases. The optimized coating shows a maximum hardness of 626 HV, small friction coefficient of 0.12 and a lower wear rate of only 3.1 × 10−5 ± 0.15 mm3 N−1 m−1, indicating excellent long-term self-lubrication property and wear resistance.