A high accuracy diffusion kinetics formalism for random multicomponent alloys: application to high entropy alloys

In this paper, a new, lighter, version of the highly accurate Moleko, Allnatt and Allnatt formalism for describing both tracer (self) and collective diffusion kinetics in multicomponent random alloys is presented. Verification of the resulting expressions is performed by means of kinetic Monte Carlo simulation. The accuracy of the new formalism is much higher than that of the combined Manning and Holdsworth and Elliott formalism discussed recently. Using this formalism the possible range of the tracer diffusion ratio of the highest to the lowest atomic component is examined for equiatomic (or near equiatomic) binary, ternary, quaternary and quinary alloys. It is shown that in the random alloy model, the correlation effect is the highest with a reduction of the fastest tracer diffusion by 40–55%, when moving from two pure metals to their equiatomic binary alloy. By adding the third component (with an intermediate mobility) this effect can be further increased with a possible total reduction of the fastest tracer diffusion by up to 70% (depending on the combinations of mobilities), while adding the fourth component brings this reduction up to 80% and with a possible maximum of up to 85% reduction for the 5-component alloy (again depending on the combinations of mobilities). But the slowest diffusing components are not affected by this. This suggests that kinetics arguments alone are not enough for explaining the sluggish diffusion observed of all atomic components in (equiatomic) high-entropy alloys.本文提出了一种全新且更轻量化的高精度Moleko、Allnatt与Allnatt形式化理论，该理论可用于描述多组分无序合金中的示踪（自）扩散与集体扩散动力学过程。本文通过动力学蒙特卡洛（Kinetic Monte Carlo）模拟对所得到的表达式进行了验证，且该新形式化理论的精度远高于近期讨论的Manning、Holdsworth与Elliott联合形式化理论。借助该形式化理论，本文针对等原子比（或近等原子比）的二元、三元、四元及五元合金，探究了最高与最低原子迁移率组分的示踪扩散比的可能取值范围。研究表明，在无序合金模型中，当从两种纯金属转为其等原子比二元合金时，关联效应最为显著，最快示踪扩散速率可被降低40%至55%；通过添加具备中等迁移率的第三组分，该效应可进一步增强，最快示踪扩散速率的总降幅最高可达70%（具体取决于迁移率的组合方式），而添加第四组分时，该降幅可提升至80%，五元合金的最大降幅甚至可达85%（同样取决于迁移率的组合方式）。但扩散速率最慢的组分不受该效应影响，这表明仅依靠动力学理论无法完全解释（等原子比）高熵合金（High-Entropy Alloys）中所有原子组分所表现出的迟滞扩散现象。