Anisotropic diffusion in symmetric tilt grain boundaries in bcc iron: A DFT study

Abstract

Diffusion analysis at the atomic scale in three orthogonal directions for both low- and high-energy symmetric tilt grain boundaries (GBs) in bcc iron is presented. Using DFT, we report (i) the energetically preferable configurations of point defects in the GBs (112) and (210) as well as in surrounding atomic layers; (ii) the activation barriers for vacancy and self-interstitial hopping in the GB plane and from the GBs to a nearest atomic layer; (iii) the attempt frequencies in each diffusion direction. The obtained values are refined by taking into account the temperature dependence of magnetization. It has been shown that interstitial and combined interstitial-vacancy mechanisms agree with the experimental data on self-diffusion in bcc iron. The temperature dependencies of the diffusion coefficient are obtained as Arrhenius law taking into account transition between ferro- and paramagnetic states. They provide insight into transport processes at relatively low temperatures which can be important for practical applications.