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.