Mechanism of oxygen adsorption on surfaces of γ-TiAl

We studied the adsorption behavior of oxygen on low index surfaces of γ-TiAl via first principles to investigate the mechanism that drives the adsorption behavior. The (100) surface is the most stable surface energetically followed by the (111), (110) and (001) surfaces. A study of the adsorption of a single oxygen atom on surfaces of TiAl showed that the O atom prefers the Ti-rich environment that has a high potential of generating TiO2. Competition between O-Al bonding and O-Ti bonding was observed in the O adsorbed surface regions. However, the O-Ti interaction dominates the adsorption behavior in all considered systems except when O is adsorbed on an Al-terminated (001) surface as the O–Al bond is stronger than O–Ti bond. A linear relationship between adsorption energy and integration of orbital overlaps between the O atom and the metals is obtained, which indicates that the electronic structure controls the adsorption behavior of an O atom on a γ-TiAl surface — an opportunity to improve the oxidation resistance of γ-TiAl based alloys.