[论文解读] Transition metal solute interactions with point defects in austenitic iron from first principles

D. J. Hepburn, E. MacLeod+1 more|arXiv (Cornell University)|Jul 30, 2014

Fusion materials and technologies被引用 5

一句话总结

这项第一性原理研究揭示，在面心立方（austenitic）铁中，尺寸过大的过渡金属溶质由于局部应力场的作用，会强烈捕获空位和自间隙原子，从而降低缺陷的迁移率和净缺陷浓度。这解释了实验中观察到的奥氏体钢中肿胀和辐照诱导偏析减少的现象，其中尺寸过大的溶质（如Ti、Zr和Hf）作为有效的缺陷阱和原位空位簇及位错环的成核位点。

ABSTRACT

We present a comprehensive set of first principles electronic structure calculations to study transition metal solutes and their interactions with point defects in austenite. Clear trends were observed across the series. Solute-defect interactions were strongly correlated to the solute size factors, consistent with local strain field effects. Strong correlations with results in ferrite show insensitivity to the underlying crystal structure in Fe. Oversized solutes act as strong traps for vacancy and self-interstitial defects and as nucleation sites for the development of proto-voids and small self-interstitial loops. The reduction in defect mobility and net defect concentrations explains the observed radiation-damage resistance in austenitic steels doped with oversized solutes. Oversized solutes remaining dissolved in oxide dispersion-strengthened (ODS) steels could contribute to their radiation-damage resistance. Ni and Co diffuse more slowly than Fe, along with any vacancy flux produced under irradiation below a critical temperature, which is 400 K for Co and their concentrations should be enhanced at defect sinks. Cr and Cu diffuse more quickly than Fe, against a vacancy flux and will be depleted at defect sinks. Oversized solutes early in the transition metal series form highly-stable solute-centred divacancy (SCD) defects with a nearest-neighbour vacancy. The vacancy-mediated diffusion of these solutes is dominated by the dissociation and reassociation of the SCDs, with a lower activation energy than for self-diffusion, which has important implications for the nucleation and growth of complex oxide nanoparticles containing these solutes in ODS steels. Interstitial-mediated solute diffusion is energetically disfavoured for all except Cr, Mn, Co and Ni. The central role that solute size plays in the results presented here means they should apply to other solvent metals and alloys.

研究动机与目标

• 理解掺杂了尺寸过大的过渡金属溶质的奥氏体钢中肿胀和辐照诱导偏析减少的原子尺度机制。
• 研究溶质尺寸和电子结构如何影响面心立方（奥氏体）铁中溶质-缺陷相互作用。
• 评估尺寸过大的溶质在氧化物弥散强化（ODS）钢中的作用，特别是溶解的溶质是否有助于提高抗辐射损伤能力。
• 分析过渡金属溶质在奥氏体中通过空位和间隙原子介导的扩散路径。
• 建立溶质性质（尺寸、电子结构）与缺陷结合能之间的功能关系。

提出的方法

• 在面心立方（fcc）Fe中对替代型过渡金属溶质执行全势线性化原子轨道平面波（FP-LAPW）电子结构计算，基于密度泛函理论（DFT）。
• 计算溶质在不同构型和距离下与空位及自间隙缺陷（SIs）的结合能。
• 计算靠近溶质的空位跳跃迁移能以及通过空位介导和间隙介导路径的溶质扩散迁移能。
• 采用解离的空位跳跃路径（ω3、ω4）来模拟溶质存在下的缺陷迁移，施加约束以避免非物理构型。
• 分析以溶质为中心的双空位（SCD）缺陷的形成与稳定性，尤其关注早期过渡金属。
• 与体心立方（bcc）Fe的结果进行比较，以评估缺陷-溶质相互作用对晶体结构的敏感性。

实验结果

研究问题

• RQ1 溶质尺寸和电子结构如何影响过渡金属溶质与奥氏体铁中点缺陷之间的结合能？
• RQ2 局部应力场在溶质-缺陷相互作用中的作用是什么？这与溶质尺寸因子有何相关性？
• RQ3 在辐照条件下，Ni/Co（扩散速率慢于Fe）与Cr/Cu（扩散速率快于Fe）的空位介导溶质扩散有何不同？
• RQ4 以溶质为中心的双空位（SCD）缺陷的稳定性和形成机制是什么？它们如何影响溶质扩散？
• RQ5 溶质-缺陷相互作用在多大程度上对基底晶体结构（如fcc与bcc Fe）不敏感？

主要发现

• 尺寸过大的溶质（如Ti、Zr、Hf）对空位和自间隙原子均表现出强结合能力，某些情况下结合能超过1 eV，表明其具有有效的捕获能力。
• Ni和Co的空位介导扩散速率慢于Fe的自扩散，其临界温度为400±50 K；低于此温度时，溶质通量在缺陷阱处增强。
• Cr和Cu在空位通量作用下扩散速率快于Fe，导致在缺陷阱处发生贫化，与实验观测的RIS趋势一致。
• 早期过渡金属溶质（如Ti、V、Cr）可形成高度稳定的以溶质为中心的双空位（SCD）缺陷，其最近邻为空位，从而降低扩散的活化能。
• 除磁性元素（Cr、Mn、Co、Ni）外，所有溶质的间隙介导扩散路径在能量上均不利，这些磁性元素仅表现出微弱的间隙扩散路径。
• fcc Fe中结合能与缺陷相互作用与bcc Fe中高度相似，表明缺陷-溶质相互作用对晶体结构不敏感，且可推广至铁的多种同素异形体。