In situ surface analytical investigation of the thermal oxidation of Ti-Al intermetallics up to 1000 °C

The low pressure high temperature oxidation behavior of Ti-Al intermetallics are of interest to power technology aiming to synthesize this material by sintering of powders. This paper presents in situ surface analytical studies of the composition of a two-phase TiAl/Ti3Al bulk microcrystalline system after oxidizing the same (sputtered) reference surface for 30 min at various oxygen partial pressures and temperatures varying between room temperature (RT) and 1000 degreesC. The results show that oxidation already begins at very low (<5 x 10(-10) mbar) oxygen pressure, producing Al2O3 and the lower oxidation states of Ti. As the oxygen pressure and oxidation temperature increases, TiO2 becomes dominant up to 900 degreesC. No phase transition of Al2O3 has been observed in this range. No sign of a blocking behavior of the oxide layer is seen. At 1000 degreesC a new oxide phase, Al2TiO5 appears, changing the composition and behavior of the surface drastically. The observed results can be explained by qualitative thermodynamic arguments. The thickness and composition of the oxide overlayer is, however, primarily determined by the oxygen supply. (C) 2002 Published by Elsevier Science B.V.