摘要
利用基于密度泛函理论的第一性原理计算了γ-TiAl(100)表面附近空位、Si和W掺杂的形成能,以及它们对O原子在该表面附近吸附和扩散的影响.计算结果表明,在掺杂体系中,Si原子更容易替代表面第1层Al原子的位置,而W原子更容易替代表面第2层Ti原子的位置,且2者均使其近邻吸附O原子的吸附能升高.因此,Si更容易偏析在表面第1层上,而W更容易偏析在表面第2层上,且抑制了O原子在γ-TiAl(100)表面的吸附.在空位缺陷体系中,表面第1层Ti原子空位比Al原子空位更易形成.在干净表面、Ti空位表面,Si掺杂和W掺杂表面体系中,O原子从表面上到表面下第2层扩散的能垒分别为1.98,1.34,2.53和2.69 eV,相对于干净表面,Ti空位缺陷的形成使得O原子在,γ-TiAl(100)表面附近的扩散更加容易,而Si和W掺杂使得O原子在γ-TiAl(100)表面上的扩散更加困难.
γ-TiAl intermetallics have attracted much interest in the last decade as prospective structural materials for aerospace applications, since they maintain a large number of outstanding properties, such as high melting point, low density and high-temperature strength. However, the oxidation resistance of TiAl alloys is inadequate at high temperature, hindering their practical applications. In order to improve the oxidation resistance, an understanding of the growth mechanisms of these surface oxides is of great importance. The adsorption and diffusion of oxygen atom at the surface are the important processes in the oxidation. In this work, the effects of point defects on the adsorption and diffusion of oxygen at γ-TiAl （100） surface are studied by the means of first-principles calculations. The calculated results of the formation energies of the point defects show that in the doped γ-TiAl （100）, the alloying Si atom prefers occupying the first surface layer Al site, while W prefers to occupy the second sublayer Ti site at theγ-TiAl （100） surface, and both of them increase the absorption energies of oxygen atom, which is the near neighbour of them. It indicates that Si prefers to segregate at the first surface layer and W prefers to segregate at the second sublayer, 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. Furthermore, the diffusion of oxygen atom at the γ-TiAl （100） surface are studied by the method of Climbing-image Nudge Elastic Band. The calculated diffusion barriers of oxygen atom from the position on the surface to the second sublayer in these systems of perfect, Ti vacancy, Si and W doped are 1.98, 1.34, 2.53 and 2.69 eV, 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.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2013年第11期1387-1391,共5页
Acta Metallurgica Sinica
基金
国家自然科学基金资助项目50871071~~
