Preparation and formation mechanism of anodic coatings co-doped with Ga, Si, and P ions on Ti–6Al–4V alloys

In this study, gallium (Ga) ions, known to be effective against both bacteria and cancer, was incorporated into micro-arc oxidation (MAO) coatings on Ti–6Al–4V alloys. In a fixed solution of 5 g/L Na3PO4, the influences of Ga(NO3)3 concentration, Na2SiO3 concentration, Na2SO4 concentration and treatment time on coating properties were studied by using an orthogonal experiment to prepare Ga-Si-P coatings. In addition, the roles of each electrolyte on coating formation were clarified by using signal factor experiments. The results show that the raised Ga(NO3)3 concentration and current density continually increase the Ga content, showing that the Ga ions enter into MAO coatings by both diffusion and electromigration. Ga(NO3)3 is harmful for coating formation, while Na2SO4, Na2SiO3 and Na3PO4 act as film-forming agents. The Si content is negatively related to the P content resulted from the competition between Na2SiO3 and Na3PO4 to take part in the coating formation, while the P content is positively related to the Ga content attributed to the main existence form of Ga ions in MAO coatings as amorphous Ga2O3 and GaPO4.