Plasma electrolyte oxidation of hydroxyapatite-containing coating on AZ31B Mg alloy: Effects of current density and duty cycle

Plasma electrolytic oxidation (PEO) procedure has been considered as a proper method to increase the corrosion resistance of Mg alloys. In this study, the effect of current density and duty cycle as the operating parameters on the corrosion behavior of coatings at a constant frequency was studied. Also, hydroxyapatite nanoparticles were added to the electrolyte to improve the biological activity of the final coating. The top and cross-section view of the coatings was studied using scanning electron microscopy (SEM) to explore the microstructure changes by the operating parameters. The corrosion performance of coatings was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) assays in simulated body fluid (SBF), respectively. The appropriate current density selection of 300 mA/dm2 and a duty cycle of 50 % confirmed the high corrosion resistance of obtained coating because of the morphology of the coating. At the optimum parameters, the results of the in vitro immersion test showed that the coating containing hydroxyapatite has higher biological activity, and also it could protect the coating for a longer period of time.