| The surface oxidation of metals and intermetallics affects their application and development. Among them, the surface oxidation of TiAl alloys become the focus of the research in this field. The first-principles calculations were used to study the effects of the point defects on the adsorption and diffusion of oxygen at the γ-TiAl(100) surface.The most stable adsorption site above the γ-TiAl(100) surface is the hollow site (H), and the one in the second sub-surface layer is the center of the rectangular pyramid (P). The diffusion barriers of oxygen atom on the γ-TiAl(100) surface is0.62eV. The diffusion barriers of oxygen atom from the most stable position on the surface to the second sub-layer in the γ-TiAl(100) surface is1.98eV. Therefore, it can be found that the diffusions of oxygen atoms on the γ-TiAl(100) surface are easier. The diffusion barrier of oxygen atom from the second to the third sub-layer in the γ-TiAl(100) surface is1.34eV, which is equal to that of the diffusion of oxygen atom in the y-TiAl bulk system. In the doped system, the alloying Si atom prefers occupying the first surface layer Al site, while W prefers substituting the Ti atom in the second sub-layer at the γ-TiAI(100) surface, and both of them increase the absorption energies of oxygen atom, which is the near neighbor of them. It indicates that Si prefers to segregate at the first surface layer and W prefers to segregate at the second sub-layer, and both of them can suppress the adsorption of oxygen atoms at the γ-TiAl(100) surface. In the defect of vacancy system, the Ti vacancy is easier to be formed than Al vacancy on the first surface layer. The diffusion barriers of oxygen atom from the position on the surface to the second sub-layer in these systems of perfect, Ti vacancy, Si and W doped are1.98eV,1.34eV,2.53eV and2.69eV, respectively. It indicates that the diffusion of oxygen atom is made easier by the Ti vacancy, while it is more difficult by the dope of Si and W. |
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