Influence of moisture on the oxidation of gamma-TiAl

The influence of water vapour on the oxidation of Ti-50 at.% Al was studied at 900 degrees C. Thick, well-adherent oxide scales were formed consisting of an outer TiO2 layer and an inner heterogeneous mixture of TiO2 and Al2O3. The interface between these layers is marked by large pores and Al2O3 particles embedded in TiO2. No compact Al2O3 barrier 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 pressure.