<Original Paper>Characterization of the Oxide Films Formed on the Surfaces of Nb and Y Deposited TiAl Substrates by Oxidizing under the Low Oxygen Pressure

X-ray photoelectron spectroscopy has been used for investigating the oxide layer formed on the surfaces of TiAl, and Al, Nb and Y deposited TiAl substrates by oxidizing under an atmosphere of 10^ Pa in the temperature range of 1073 to 1273K for 6ks. Titanium oxide films containing aluminum oxide, even in the Nb and Y coating cases, were formed on the TiAl. Ti in the oxide films was found to be in the oxidation states of +4 and +3 for TiAl and Nb deposited TiAl, and +2 and +3 for the Y deposited TiAl, respectively. Nb is likely to be in the high level oxidation state in the oxide layers containing TiO_2 at high temperatures. The proportions of Ti in the oxidation state of +4 for TiAl and Nb deposited TiAl increase as temperature rises. Preferential aluminum oxide formation appears to be promoted by Y coating, whereas Y would increase the amount of oxygen vacancy in the TiO_2 layer for which oxygen diffusion is predominant. It is noteworthy that Ti in the oxide film for Y coating is in the low level oxidation state at the oxygen pressure which enables to oxidize titanium