Effects of Nb and Si on high temperature oxidation of TiAl
(1. School of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics,Beijing 100083, China;2. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
Abstract: The isothermal oxidation behavior of TiAl based alloys at 900 ℃ in air with a combination of Nb (5%−10%, mole fraction) and Si (1%−5%, mole fraction) was investigated. The microstructure and the composition of the oxidation scale were studied by using XRD, TEM and EPMA. The results show that the combination of Nb and Si can improve the oxidation resistance of the alloys significantly. The element Si can change the typical microstructure of oxidation scale on TiAl based alloys. In alloys with Si addition, the compact Al2O3 forms in the interior side of oxidation scale. When x(Si)＞3%, the Ti5Si3 phase forms and the coarse crystal TiO2 forms on Ti5Si3 phase after oxidation. The increase of Nb content in the TiAl based alloys impedes the growth of Ti5Si3 phase, and the formation of TiO2 on surface and on Ti5Si3 phase is also impeded.
Key words: TiAl based alloy; niobium silicon alloying; isothermal oxidation behavior; oxidation resistance