Surface characterization of the oxide layer grown on Ti-Nb-Zr and Ti-Nb-Al alloys

Abstract

The surface of the oxide layers formed after oxidation in air at 750°C of three titanium alloys has been characterized by several techniques. The investigated alloys were Ti7Nb6Al, Ti13Nb13Zr and Ti15Zr4Nb, with potential applications as biomaterials. XPS experiments showed that, after 24 h exposure, the surface of the Ti7Nb6Al alloy is mainly formed of Al2O3, with a minor presence of TiO2, and absence of Nb oxide. On the other hand, the surface of both TiNbZr alloys is mainly composed of TiO2, with some amount of ZrO2 and Nb2O5. An enrichment of the Nb signal is observed in both samples with respect to the bulk composition. The topography and surface morphology of the oxidized alloys were investigated by atomic force microscopy. A more regular surface topography was observed for the Ti7Nb6Al alloy than for the TiNbZr alloys and, consequently, a higher potentiality in biomedical applications. Finally, in order to get in-depth information of the oxide scale, Rutherford backscattering spectroscopy experiments were also performed. The results obtained with this technique confirm those obtained by XPS, and can help to understand the mechanism and kinetics of the oxide film formation.