Formation of Hydroxyapatite Produced by Microarc Oxidation Coupled with Sol-gel Technology

Bioactive composite coatings containing hydroxyapatite on magnesium alloy AZ91D are prepared successfully by microarc oxidation (MAO) coupled with sol-gel treatment. The morphologies of the composite coatings formed by MAO treatment at 0.5 A · cm−2 current density coupled with sol-gel treatment appear to be much denser and smoother than the coatings produced at 1.0 A · cm−2. The Ca/P ratio (1.70) of the composite coatings produced at 0.5 A · cm−2 is slightly higher than the ratio of the sol prepared (1.67), due to the substitute groups in apatite lattice according to the Fourier transform infrared spectroscopy test. Moreover, electrochemical tests illustrate that the composite coatings (0.5 A · cm−2) have higher open-circuit potential, corrosion potential, and corrosion resistance than the composite coatings at 1.0 A · cm−2. Immersion tests have been performed showing an enhanced bioactivity and apatite-forming ability. Consequently, combining the MAO and sol-gel treatments provides a promising candidate for further investigation.