Oxidation Behavior of Ti-22Al-25Nb Alloy at 750 ℃ and 850 ℃

The isothermal and cyclic oxidation behavior of Ti-22Al-25Nb alloy in air at 750 ℃ and 850 ℃ were investigated by thermogravimetry. The phase composition, microstructure and element distribution of the oxide layer were analyzed by means of XRD, SEM and EDS. The results show that the oxidation resistance of the alloy is closely related to temperature and oxidation mode. The oxidation kinetics curves of Ti-22Al-25Nb alloy at 750 ℃ in two oxidation modes accord with the parabolic law. At 850 ℃, the oxidation kinetic curves of the two oxidation modes conform to the linear law in the later stage of oxidation. Cyclic oxidation has a faster oxidation rate at the same test temperature. The main oxidation products of the alloy under different experimental conditions all are TiO₂, Al₂O₃, Nb₂O₅and AlNbO₄. The relative content of oxides is different under different experimental conditions, and AlNb₂is formed at 850 ℃. The increase of non-protective oxides TiO₂ and AlNbO₄ in the oxide film is the main reason for the decrease of the oxidation resistance of the alloy.