Concentrated single phase solid solutions, including medium- and high-entropy alloys, represent a new class of materials that have recently attracted significant interest due to exceptional functional and structural properties. Their fascinating properties are mainly attributed to the sluggish atomic-level diffusion and transport, but its controlling mechanisms are largely unknown and there is certain skepticism about its very existence. By using microsecond-scale molecular dynamics, on-the-fly and conventional kinetic Monte Carlo, we reveal the governing role of percolation effects and composition dependence of the vacancy migration energy in diffusion. Surprisingly, an increase of concentration of faster species (Fe) in face-centered cubic Ni-Fe alloy may decrease the overall atomic diffusion. Consequently, the composition dependence of tracer diffusion coefficient has a minimum near the site percolation threshold, ∼20 at.%Fe. We argue that this coupled percolation and composition-dependent barriers for vacancy jumps within different subsystems in medium- and high-entropy alloys leads, indeed, to the sluggish diffusion. A fast method for preselecting materials with potentially desired properties is suggested.

浓缩的单相固溶体，包括中熵和高熵合金，代表了一类新型材料，由于其卓越的功能和结构特性，最近引起了人们的极大兴趣。它们的引人入胜的性质主要归因于原子级扩散和迁移的缓慢，但是其控制机制在很大程度上尚不为人所知，并且对其存在的确有一定的怀疑态度。通过使用微秒尺度的分子动力学，动态的和常规的动力学蒙特卡洛方法，我们揭示了渗流作用和空位迁移能在扩散中的成分依赖性的支配作用。出人意料的是，面心立方Ni-Fe合金中更快的物种（Fe）的浓度增加可能会降低整体原子扩散。所以，示踪剂扩散系数的成分依赖性在位点渗漏阈值附近最低，约为20 at。％Fe。我们认为，在中，高熵合金的不同子系统中，空位跃迁的耦合渗流和成分依赖性势垒确实导致了扩散缓慢。建议使用一种快速选择具有潜在所需特性的材料的方法。