Effect of applied voltage on phase components of composite coatings prepared by micro-arc oxidation

• Coatings prepared on biomedical titanium substrate by micro-arc oxidation
• Coatings composed of titania, hydroxyapatite and calcium carbonate
• Hydroxyapatite on the coating surface can enhance the surface bioactivity.

In this report, we present results from our experiments on composite coatings formed on biomedical titanium substrates by micro-arc oxidation (MAO) in constant-voltage mode. The coatings were prepared on the substrates in an aqueous electrolyte containing calcium acetate and β-glycerol phosphate disodium salt pentahydrate (β-GP). We analyzed the element distribution and phase components of the coatings prepared at different voltages by X-ray diffraction, thin-coating X-ray diffraction, electron-probe microanalysis, and Fourier-transform infrared spectroscopy. The results show that the composite coatings formed at 500 V consist of titania (TiO2), hydroxylapatite (HA), and calcium carbonate (CaCO3). Furthermore, the concentration of Ca, P, and Ti gradually changes with increasing applied voltage, and the phase components of the composite coatings gradually change from the bottom of the coating to the top: the bottom layer consists of TiO2, the middle layer consists of TiO2 and HA, and the top layer consists of HA and a small amount of CaCO3. The formation of HA directly on the coating surface by MAO technique can greatly enhance the surface bioactivity.