Oxidation behavior of in-situ Al2O3/TiAl composites at 900°C in static air

In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900°C in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2+Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with finer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals and promoting the stable formation of the Al2O3-riched layer, which is beneficial to improve the oxidation properties.