On the complexity of solid-state diffusion in highly concentrated alloys and the sluggish diffusion core-effect

Abstract Diffusion paths in system V – Nb – W – Al in the highly concentrated region (i.e. as “High Entropy Alloys”) are modelled using DICTRA code with commercial databases and with a new algorithm, based on the Cluster Variation Method (CVM). The DICTRA simulations, which produce realistic diffusion profiles, show that the diffusion path is non-linear. The CVM simulations, with parameters obtained by ab initio calculations, allow to investigate in an incremental way the effects of thermodynamics, of correlations and the role of the intrinsic diffusivities of the components. The results confirm the non-linear character of the diffusion path, and show that it is primarily driven by the complex thermodynamics characteristic of these alloys. When the intrinsic diffusivities are used, it is observed that the slowest diffusing species (in the present case, W) will constrain the whole diffusion process. This is likely the origin of the so called “sluggish diffusion” effect and it is of kinetic origin, bearing no relation with the configurational entropy.