Microstructure and Corrosion Characterization of a MgO/Hydroxyapatite Bilayer Coating by Plasma Electrolytic Oxidation Coupled with Flame Spraying on a Mg Alloy

[Image: see text] Thermally sprayed hydroxyapatite coatings are one of the main strategies to improve the bioactivation of metal implants. However, the naturally low corrosion resistance of these coatings is the main challenge for their use. In this study, plasma electrolytic oxidation (PEO) was used to create an intermediate layer. The anodization process was used for comparison. According to the polarization curves, the PEO layer was more effective than the anodized layer in reducing the corrosion current density (I(corr) of 0.05 × 10(–9) A/cm(2) vs I(corr) of 0.05 A/cm(2)). The results of electrochemical impedance spectroscopy showed higher resistance of the sample with a PEO interlayer than that of the sample with an anodized interlayer. The results of the hydrogen evolution test revealed that the PEO layer as a middle layer served as the main barrier for reducing the magnesium corrosion rate, especially during the initial immersion time.