Time-resolved in-situ XRD study on oxidation evolution of Ti2AlNb-based alloys

Ti2AlNb-based alloys have long been recognized as excellent high-temperature structural materials for aerospace applications. However, the poor oxidation resistance at high temperatures is still one of the main barriers to its practical uses. In this study, the oxidation rate of Ti2AlNb-based alloys at 1100 celcius was deliberately slowed down by reducing the air content so that the new phases and oxidates were determined by time-resolved in-situ X-ray diffraction (XRD). It is shown that the Ti2AlNb-based alloys first formed orthorhombic phase (O phase) on surface by diffusional transformation and then the O phase gradually transformed into & alpha;2 phase subsequently which means the O phase decomposed due to excessive oxygen entering their lattices. Then Ti, Al, and Nb co-formed TiO2 doped with Al and Nb in the layer. Because of the different diffusion rates, the subsequently formed oxide scales were mainly composed of aluminum oxide (Al2O3) and rutile - TiO2. A Ti depletion layer as well as Al, Nb enriched layers was disclosed by ToF-SIMS results. This study contributes to understand the initial oxidation evolution mechanism and promotes the oxidation resistance of Ti2AlNb-based alloys.