A first-principles study of the diffusion coefficients of alloying elements in dilute alpha-Ti alloys
A first-principles study of the diffusion coefficients of alloying elements in dilute alpha-Ti alloys
复制标题
稀α-Ti合金中合金元素扩散系数的第一性原理研究
DOI：
10.1039/c6cp01899h
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发表时间：
2016
影响因子：
3.3
通讯作者：
Liu Z. K.
中科院分区：
文献类型：
--
作者：
Xu W. W.;Shang S. L.;Zhou B. C.;Wang Y.;Chen L. J.;Wang C. P.;Liu X. J.;Liu Z. K.
采用第一性原理计算方法，结合过渡态理论和八频模型，研究了Al，V，Nb，Ta，Mo，Zr，Sn等替代合金元素X在稀α-Ti合金中的扩散系数.合金元素Mo和Al在稀相α-Ti合金中的扩散速率分别出现最大值和最小值。发现最近邻溶质空位结合能和激活能与溶质原子引起的体积变化大致成反比。这种趋势有两个例外：Al和Mo。除了物理效应（即，溶质尺寸），阐明了控制溶质在稀α-Ti中扩散的另外两个关键因素：X-Ti对的化学键特征和振动特征。结果表明，Mo的超快扩散是由于Mo与Ti原子的金属键相互作用及其对晶格振动的低频贡献，而Al的共价键性质及其对晶格振动的高频贡献导致了Mo的超低扩散.此外，扩散系数的相关效应对于大溶质Ta、Nb和Zr是不可忽略的，其中溶质-空位直接迁移势垒远小于溶剂-空位迁移势垒。
Using first-principles calculations accompanied by the transition state theory and an 8-frequency model, we present a comprehensive investigation of the diffusion coefficients of substitutional alloying elements X in dilute α-Ti alloys, where X denotes Al, V, Nb, Ta, Mo, Zr, and Sn. The alloying elements Mo and Al exhibit a maximum and a minimum diffusion rate in dilute α-Ti alloys, respectively. It is found that the nearest-neighbor solute–vacancy binding energies and activation energies are roughly inversely proportional to the volume changes induced by solute atoms. There are two exceptions to this trend: Al and Mo. Besides the physical effect (i.e., solute size), two other key factors governing solute diffusion in dilute α-Ti are clarified: the chemical bonding characteristics and vibrational features of X–Ti pairs. It verifies that the ultrafast diffusivity of Mo arises from the interactions with Ti atoms by metallic bonds and its low-frequency contributions to lattice vibration, while the more covalent bonding nature and the high-frequency contributions to the lattice vibration of Al lead to its ultraslow diffusivity. In addition, the correlation effects of diffusion coefficients are non-negligible for the large solutes Ta, Nb, and Zr, in which the direct solute–vacancy migration barriers are much smaller than the solvent–vacancy migration barriers.