Soft x-ray absorption spectroscopy study of oxide layers on titanium alloys

Abstract

Soft x-ray absorption spectroscopy (XAS) has been used to perform chemical analysis of oxide films formed after contact with air, both at room temperature and at 750 ◦C, on three titanium alloys. The alloys investigated were Ti–13Nb–13Zr, Ti–15Zr–4Nb and Ti–7Nb–6Al. Soft x-ray absorption spectra were taken at the Ti 2p and O 1s edges. The spectra corresponding to the room-temperature-oxidized samples are similar for the three alloys and show the presence of native oxide with a small metallic contribution. For the heat-treated samples, the alloying elements as well as element diffusion play a significant role in the formation of the oxide layer. In this case, the spectra exhibit clear differences between the TiNbZr alloys and Ti–7Nb–6Al. The oxide layer of the two TiNbZr alloys for the different heat treatment times is composed of TiO2 in the form of rutile. However, for Ti–7Nb–6Al short heat treatments give rise to the formation of Al2TiO5. By increasing the oxidation time, an Al2O3 layer grows on the initial oxide film, becoming thicker as the exposure time is enhanced.