Abstract It is well known that Fe, Co and Ni are characterised by abnormally fast diffusivity in the hcp phase of Ti (α-Ti). Their diffusivity values are 10 5 times higher than self-diffusion data, which is atypical for vacancy-mediated diffusion yet too slow for interstitial diffusion. Also, addition of Fe, Co and Ni appears to accelerate the solvent diffusivity, with dramatic ramifications on a number of diffusion-controlled mechanisms. The fast diffusivity of these elements in α-Ti seems to be the result of their ability to dissolve both interstitially and substitutionally. In fact, while the majority of Fe, Co and Ni atoms sit substitutionally within the hcp lattice, a small concentration of these solute atoms can move very fast through interstitial sites, determining the high diffusion coefficient values. In this work, a combination of density functional theory and Kinetic Monte Carlo simulations is used to investigate possible migration processes for both solute and solvent atoms and their effect on the macroscopic diffusivity. We find that traditional classical interstitial sites are unsuitable for these solute atoms, and that alternative interstitial sites are instead preferred. Calculations confirm that the fast diffusivity of these solute atoms is a result of their ability to diffuse both interstitially and by vacancy-mediated mechanisms, yielding excellent agreement with experimental values. It is possible for these solute atoms to swap position with solvent atoms without the presence of vacancies, leading to an accelerated solvent diffusion in the presence of relatively dilute levels of these solute elements.

中文翻译：

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hcp-titanium中的非经典间隙位点和异常扩散机制

摘要 众所周知，Fe、Co 和Ni 在Ti (α-Ti) 的hcp 相中具有异常快速的扩散特性。它们的扩散率值比自扩散数据高 10 5 倍，这对于空位介导的扩散是非典型的，但对于间隙扩散来说太慢了。此外，添加 Fe、Co 和 Ni 似乎会加速溶剂扩散，对许多扩散控制机制产生显着影响。这些元素在 α-Ti 中的快速扩散似乎是它们能够以间隙和置换方式溶解的结果。事实上，虽然大多数 Fe、Co 和 Ni 原子替代地位于 hcp 晶格内，但这些溶质原子的小浓度可以非常快速地通过间隙位点，从而确定高扩散系数值。在这项工作中，密度泛函理论和动力学蒙特卡罗模拟相结合，用于研究溶质和溶剂原子的可能迁移过程及其对宏观扩散率的影响。我们发现传统的经典间隙位点不适合这些溶质原子，而替代的间隙位点是首选。计算证实，这些溶质原子的快速扩散是它们通过间隙和空位介导机制扩散的能力的结果，与实验值非常吻合。这些溶质原子有可能在不存在空位的情况下与溶剂原子交换位置，导致在这些溶质元素相对稀的情况下加速溶剂扩散。