Evaluation of TiO₂/CeO₂ coating on Ti6Al4V alloy in PBS physiological medium using conventional and near field electrochemical techniques

Ti6Al4V alloy is an exceptional biomaterial compared to other metals used for implants that replace bone tissue. Despite being corrosion-resistant, Ti6Al4V can release ions that may cause adverse effects to tissues after long implantation times. Several researchers have studied the thermal oxidation of this alloy, which generated layers of mainly TiO₂ rutile phase to increase its wear and corrosion resistance. However, one of the shortcomings of these layers is their susceptibility to pitting corrosion. To extend the useful life of Ti6Al4V, a coating system consisting of thermally grown TiO₂ and CeO₂ obtained using chemical conversion treatment was proposed, which would be advantageous owing to its non-toxic, antiseptic, and anticorrosive properties. In this study TiO₂ rutile phase was obtained on the surface of Ti6Al4V after quenching at 650 °C for 90 min followed by tempering at 450 °C. Cerium conversion treatments produced a surface film consisting of Ce³⁺ and Ce⁴⁺, which was characterised using X-ray diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectronic spectroscopy, cyclic polarisation curves, electrochemical impedance spectroscopy, and scanning Kelvin probe. The obtained coating system reduced the corrosion rate of the substrate: TiO₂ worked as main passive film and the cerium coating reduced the susceptibility to pitting corrosion.