Effect of applied voltage on the structure of microarc oxidized TiO₂-based bioceramic films

Microarc oxidized (MAO) films, formed at various applied voltages (200-450 V) in an electrolyte containing EDTA-Ca and phosphate on Ti6Al4V substrate, mainly contain TiO₂ and amorphous calcium phosphate (CaP). During the ionization process of the MAO, the Ca would be released from the -N ↔ Ca ↔ OOCR- due to a tremendous thermal impact. Eventually, the amorphous CaP was formed during the plasma condensation process. All the MAO films exhibit good interfacial bonding to the substrate. With increasing the applied voltage, the Ca and P contents, Ca/P ratio, thickness and micropore size of the MAO film increase, while the micropore number declines. Ti, Ca and P elements show a uniform distribution character around the micropores. However, the inner of the micropores exhibits a high Ti concentration and low Ca and P concentrations. In addition, the MAO film shows a gradient in element distributions within the MAO film.