Characterization of thermal and anodic oxide layers on β- and on near-β-titanium alloys for biomedical application

Abstract

β- and near-β-Ti alloys for biomedical applications show a favourable mix of mechanical, biological and biocompatible properties. In this study, oxide layers on Ti13Nb13Zr, Ti15Mo5Zr3Al, Ti30Nb and Ti30Ta were prepared by thermal and anodic oxidation, in order to adjust constant, reproducible and well-defined surface properties. The thickness, the phase composition and the element composition of the oxide layers were determined. The corrosion properties were investigated by current density-potential curves under physiological conditions. Depending on the oxidation parameters, film thicknesses in the range 10-250 nm can be prepared. The thermal oxide layers consist predominantly of TiO 2 in rutile structure while the anodized samples show a mixture of anatase and amorphous TiO 2 . In addition, certain amounts of mixed oxides of titanium and alloying elements such as TiZrO 4 or TiNb 2 O 7 are found in the oxide films. The corrosion resistance of the oxidized samples is increased as compared with the polished samples whose current densities in the range of passivity are comparable to that of Ti6A14V.