Oxygen adsorption on γ-TiAl surfaces and the related surface phase diagrams: A density-functional theory study

We have constructed the surface phase diagrams for oxygen adsorption on gamma-TiAl low-index surfaces using density-functional theory calculations. From these surface phase diagrams, the selective oxidation behaviors of the gamma-TiAl surfaces and the corresponding polycrystalline systems can be easily understood and predicted. For the (100) surface, complete selective oxidation of titanium is favored and a titanium oxide layer may be produced at the initial stage of oxidation. For the (110) and (001) surfaces, only titanium oxides may form. For the gamma-TiAl polycrystalline system, O may induce complete Ti and Al surface segregations on the Ti-rich and Al-rich conditions, respectively. In addition, the microscopic oxidation mechanisms are identified and the experimental results are successfully explained. More importantly, by comparing the different TiAl surface orientations, a comprehensive surface phase diagram is constructed to study the oxidation behaviors of polycrystalline gamma-TiAl. This method can also be applied to other polycrystalline materials. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.