Nb基合金中氧原子扩散及团簇化的第一性原理

Diffusion and Clustering of Oxygen Atom in Nb-based Alloys:A First-principles

利用第一性原理计算,研究了氧原子在Nb中的扩散现象以及施加应变的影响,并对氧原子在Nb-Ti、Nb-Zr合金中的团簇化进行了计算分析。发现在单向应变下,在平行于应变方向上,氧原子的扩散势垒随着应变的增大不断减小,当应变为10%时,扩散激活能从初始的0.92eV降低至0.5eV左右;在垂直于应变方向上,氧原子更容易扩散至被拉长的八面体间隙中,即单向应变下氧原子会在Nb中沿应变方向聚集排列,这会在实际材料中导致应力的集中。计算研究了氧原子在Nb合金中的团簇化问题,发现在纯Nb中,氧原子倾向于均匀分布而不是形成氧原子对;添加合金元素Ti和Zr后,随着氧原子浓度的升高,氧原子对将在合金元素周围形成,Zr周围氧原子对的形成可使体系的能量降低0.29eV。

First-principles calculation is used to investigate the diffusion of oxygen atom under axial strain in Nb,as well as the clustering of oxygen in Nb-Ti and Nb-Zr alloys.It is found that with the increase of the axial-strain,the energy barrier in the direction parallel to the applied strain becomes lower,and when the strain is 10％,the energy barrier decreases from 0.92 eV to 0.5 eV.In the direction perpendicular to the strain,oxygen atom can diffuse into the elongated octahedral interstices more easily; therefore,oxygen atom tends to accumulate in the direction of applied strain which will lead to the stress concentration in real alloy.For the computations about the clustering of oxygen atom,it is found that in pure Nb,oxygen atom prefers to distribute uniformly in the system instead of forming atom pairs; however,when the alloying elements Ti and Zr are added,the formation of oxygen atom pairs becomes energy favorable,especially when the concentration of oxygen atom is relatively high.The result show that when one oxygen atom pair forms around Zr,the total energy of the system can be decreased by 0.29 eV.