Characterization and corrosion evaluation of TiO2:n-HA coatings on titanium alloy formed by plasma electrolytic oxidation

In the present study, a novel TiO2-based coating containing nanosized hydroxyapatite (n-HA) has been formed on commercially available Ti-6Al-4V (Grade 5) alloy substrates by the Plasma Electrolytic Oxidation (PEO) technique. The TiO2:n-HA coating deposition was provided in an aqueous solution of disodium hydrogen phosphate containing suspended hydroxyapatite nanoparticles under a pulsed bipolar current mode. The surface morphology of the formed coatings has been examined by Scanning Electron Microscopy (SEM), while the element composition of the coatings has been determined by Energy Dispersive X-ray analysis (EDS). The presence of HA nanoparticles within the formed coatings has been analyzed by Fourier Transform Infrared Spectroscopy (FTIR). The corrosion resistance of the TiO2:n-HA coatings has been studied by electrochemical methods, including open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy, and compared to the corrosion behavior of bare titanium. The results indicate that the formed PEO coatings exhibit a porous network structure with embedded n-HA particles uniformly distributed over the entire surface of the coatings. The PEO coated samples showed substantially higher corrosion resistance compared to the bare Ti-6Al-4V substrate material. The PEO-formed TiO2:n-HA layers reduce the corrosion of titanium alloy implant materials and can be used as a bioactive biomimetic coating to enhance implant surface bioactivity and osseointegration.