Preparation of HA-containing coating by one-step MAO on titanium alloys through synergistic effect of calcium gluconate and calcium glycerophosphate

In a base solution composed of calcium gluconate (CaGlu2) and magnesium gluconate (MgGlu2), the influences of calcium glycerophosphate (Ca-GP), sodium phytate (Na12Phy), phosphoric acid (H3PO4) and constant voltage on the amounts of calcium (Ca) and magnesium (Mg) elements in micro-arc oxidation (MAO) coatings were systematically investigated using an orthogonal experiment. The results show that anodic coatings with the Ca/P molar ratio of 1.35 and containing high bioactive hydroxyapatite (HA) phase are successfully fabricated using one-step MAO treatment by adjusting processing parameters. Ca ions enter into MAO coatings by both electromigration and diffusion. H3PO4 is an effective film-forming agent and the increased concentration significantly decreases both the Ca and Mg amounts. Our results show that compared with Ca-GP, CaGlu2 can effectively improve the Ca amount of anodic coatings. Sole Ca-GP or CaGlu2 cannot significantly improve the Ca amount, while Ca-GP and CaGlu2 can synergistically improve the Ca amount in MAO coatings.