XPS study of the initial stages of oxidation of α2-Ti3Al and γ-TiAl intermetallic alloys

The initial stages of oxidation of alpha(2)-Ti3Al and gamma-TiAl alloys at 650 degrees C under low oxygen pressure are shown to be characterized by three stages using XPS. Stage I is a pre-oxidation stage characterized by the adsorption and absorption of oxygen species. When the subsurface is saturated with dissolved oxygen (16 and 2 at.%, on alpha(2)-Ti3Al and gamma-TiAl, respectively), the selective oxidation of the alloy leads to the nucleation and growth of ultrathin (similar to 0.5 and similar to 1.2 nm on alpha(2)-Ti3Al and gamma-TiAl, respectively) alumina layers (stage II). The growth kinetics of the alumina layers is limited by the transport of A] in the alloy, leading to Al-depletion in the metallic phase underneath the oxide. When a critical concentration is reached (Ti82Al18 and Ti75Al25 on alpha(2)-Ti3Al and gamma-TiAl, respectively), titanium oxidation occurs (stage 111). Ti(III) and Ti(IV) oxide particles are formed at the surface of the still growing alumina layer. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.