In situ study of the scale formation on γ-TiAl during isothermal oxidation at 700°C and on heating

Time and temperature resolved X-ray diffraction as an in situ method and electron microprobe analysis for post oxidation studies were used for the investigation of the oxide scale formation on gamma-TiAl at 700 degrees C and during stepwise heating from room temperature to 950 degrees C in air and in He with 19 vol% O-2. The formation of alumina in the form of alpha-Al2O3 and of TiO2 in the form of rutile was observed in both atmospheres and additionally, TiN was found during oxidation in air. Furthermore, diffraction peaks of two phases were detected, which do not exist in the data base for X-ray diffraction JCPDS-ICDD, and are different in air (X'- and X-phase) and in He with 19vol% O-2 (Z-phase). In air, TiO2 grows faster than the alpha-Al2O3 and the growth of TiO2 is not parabolic in the first 50 hours. An oxide scale of 5 mu m thickness consisting of a mixture of alpha-Al2O3 and TiO2 is observed. In He with 19vol% O-2 the formation of TiO2 is slower than of alpha-Al2O3 resulting in a thinner oxide scale.