The isothermal and cyclic oxidation behavior of a titanium aluminide alloy at elevated temperature

The isothermal and cyclic oxidation behavior of Ti-47AI-2Mn-2Nb with 0.8 vol.% TiB2 particle-reinforced alloy was investigated in air between 700 and 1000 degrees C. In the study, the kinetics of isothermal and cyclic oxidation were performed by using a continuous thermogravimetric method which permits mass change measurement under oxidation conditions. The oxide scales and substrates were characterized by scanning electron microscopy with energy-dispersive x-ray analysis and x-ray diffraction. At 700 and 800 degrees C, the alloy showed an excellent oxidation resistance under isothermal and cyclic conditions. After exposure to air above 800 degrees C, the outer scale of the alloy was dominated by a fast-growing TiO2 layer. Under the coarse-grained TiO2 layer was the Al2O3-rich scale, which was fine-grained. At 900 and 1000 degrees C, the extent of oxidation increased clearly. The oxidation rate follows a parabolic law at 700 and 800 degrees C. However, the alloy, upon isothermal oxidation at 900 degrees C, can be divided into several stages. During the cyclic oxidation at 900 and 1000 degrees C, partial scale spallation takes place, leading to a stepwise mass change.