Enhanced Corrosion Resistance of Ti6Al4V-ELI via TiO2 and TiO2/Hydroxyapatite Nanocomposite Coatings Grown by High Frequency Plasma Electrolytic Oxidation

TiO2 and TiO2/HA composite coatings were successfully grown on Ti6Al4V-ELI (Extra Low Interstitial) alloys using the plasma electrolytic oxidation (PEO) method to improve the corrosion performance of the alloys. Three different high frequencies (1250, 1500, and 1750 Hz) were applied during the plasma electrolytic oxidation (PEO) of an electrolyte containing nano-hydroxyapatite (HA) particles to synthesize TiO2/HA nanocomposite coatings. Additionally, conventional TiO2-PEO coatings were produced at the same frequencies to compare their in vitro corrosion performance in simulated body fluid (SBF). The corrosion characteristics of the coatings were evaluated using the potentiodynamic polarization scanning (PDS) technique at 37 degrees C. The surface morphologies were examined with scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). X-ray diffraction (XRD) was used to determine phases on the surfaces. All coated samples had 2-5 times higher polarization resistance than the Ti6Al4V-ELI alloy. The highest corrosion-resistant coating was obtained in the nano-sized HA-containing coating grown at 1750 Hz.