The effect of pre-oxidation on the oxidation behaviour of Ti-alloy at 300°C in an alkaline steam

The oxide scales on Ti-alloy with and without pre-oxidation, oxidised at 300°C in an alkaline steam for approximately 13 000 h, were studied by SEM, XRD, XPS and in situ AES techniques. The result showed that the oxide scales on Ti-alloy were composed of Al2TiO5(TiO2Al2O3), TiO2, Ti3O5, Ti2O3, Al2O3 and TiO. A comparison study has been carried out between the Ti-alloy pre-oxidised and Ti-alloy without pre-oxidation, to determine the influence of pre-oxidation upon the properties of oxidation resistance. The oxidation kinetics showed that the weight gains of the pre-oxidised samples were much less than in the controlled samples. The results showed that the whole thickness of the pre-oxidised sample was thinner than that of the controlled one. In contrast, the pattern for the stable oxide scale was reversed, i.e. the pre-oxidised sample was much thicker. Thus pre-oxidation is an effective method to improve the oxidation resistance of Ti-alloys.