Synthesis of Composite Coating Containing TiO₂ and HA Nanoparticles on Titanium Substrate by AC Plasma Electrolytic Oxidation

In this study, biocompatible ceramic layers containing TiO₂ and hydroxyapatite (HA) nanoparticles (TiO₂/HA) were deposited on pure commercial titanium (Grade 2) by using plasma electrolytic oxidation and AC power supply. The coating process was carried out in five different solutions for various times at a current density of 500 mA cm⁻². To achieve the optimum conditions for thickness and microstructure, the coating process was conducted in solutions with a 3 g L⁻¹ concentration of HA nanoparticles. FESEM, XRD, and FTIR results showed that HA nanoparticles were successfully incorporated into the pores of the layer. Furthermore, the corrosion behavior of the coating layers in the simulated body fluid was investigated with potentiodynamic polarization tests. It was observed that the corrosion current density of the samples coated in solutions with nanoparticles was decreased from 874 to 15 nA cm⁻² in comparison with the coating with no HA particles. The reason for this behavior could be the presence of a composite coating containing TiO₂/HA that seems to be stable. It firmly seems that during the crystal nucleation and growth process, phosphate and calcium ions formed a complex oxidation film while the hydroxide ions in the alkaline solution were attracted to the oxide film surface by the electric field and absorbed by the apatite particle for crystal growth.