AbstractThe influence of water vapour on the oxidation of Ti‐50 at.% Al was studied at 900°C. Thick, well‐adherent oxide scales were formed consisting of an outer TiO2layer and an inner heterogeneous mixture of TiO2and Al2O3. The interface between these layers is marked by large pores and Al2O3particles embedded in TiO2. No compact Al2O3barrier layer was observed. The oxidation leads to formation of a two phase, oxygen enriched subsurface zone, which is Al‐depleted by inner oxidation of Al to Al2O3.The oxidation kinetics were followed by continuous thermogravimetry. Exposure in moist oxygen leads to an accelerated attack compared with oxidation in dry oxygen. In moist oxygen the rate is linear after a short transition period. The oxidation rate is influenced by water partial pressure and oxygen partial pr