First-principles Study Of TiAl/TiO₂Interface

TiAl alloys have been considered to be a kind of high temperature structuralmaterials to replace heavy Ni based alloys owing to their low density, high specialstrength and good creep resistance at elevated temperature. However, low oxidationresistance above850oC limits their applications. This thesis focuses on the study ofthe interaction between γ-TiAl intermetallic and its oxidation product rutile TiO₂viafirst-principles calculations. Researches include the determination of the stablestrucutre and the bonding strength of TiAl/TiO₂interface, and electronic propertiesof atoms in the interface zone.Firstly, calculations of electronic structures and stability of bulk and surface of γ-TiAl（110） were performed. It shows that the interaction between Ti and Al atomsis covalent in nature and the Al-terminated γ-TiAl（110） surface is the most stablesurface with lowest surface energy. Comparing with Al-terminated γ-TiAl（110）surface, the defect（Ti vacancy） prefers to form on Ti-terminated γ-TiAl（110）, underthe influence of the defect（Nb doping）, Al-terminated γ-TiAl（110） is more stablethan Ti-terminated γ-TiAl（110）.Secondly, the electronic structures and stability of bulk and four low indexsurfaces of rutile TiO₂were calculation. The bulk TiO₂is a typical semiconductorwith a band gap of².0eV. The （110） surface is the most stable one with the lowestsurface energy and the highest separate energy among the four low index surfaces ofTiO₂.Finally, five combinations between TiAl（110） and TiO₂（110） surfaces werestudied. The results indicate that there is a strong interaction between Al from TiAland O from TiO₂and the Al-O bonds play a major role in the interface connection.Gemotric analusis shows that the O atoms can even insert into TiAl side by Al-Ointeraction. The Al-O bond is the strongest if O locates at the bridge site between Tiand Al, which makes the connection between TiAl（110） and TiO₂（110） is strongest.Defects, the Ti vacancy and Nb dopant, lower the bonding strength and the stabilityof the interfaces and affect the relative stability of the interfaces. They turn thecombination of the O locates at the bridge between defect and Ti in TiAl（110）surface becomes the most stable one. They benefit to prevent the formation of thenon-protective TiO₂film.