Effect of Grain Boundary on Diffusion of P in Alpha-Fe: A Molecular Dynamics Study

M Mustafa Azeem,Muhammad Zubair,Yue Zhang,Qingyu Wang,Shengbo Liu

doi:10.3389/fphy.2019.00097

Abstract

In this study, we have investigated the effect of the grain boundary (GB) on the diffusion of a Phosphorus (P) atom in alpha-Fe using molecular dynamics simulations. A Fe-P mixed dumbbell is created in the six symmetric tilt grain boundary (STGB) models. The dumbbells are allowed to migrate at different temperatures from 400 K to 1000 K, with starting positions between 5 Å to 10 Å away from the GB core. The trajectories and mean square displacements (MSD) have been recorded to analyze the diffusion details. The Nudged Elastic Band (NEB) method has been used to study the energy barrier at different positions around the GBs. Our simulation results demonstrate that the GB structure affects the diffusion mechanisms of Fe-P dumbbell. The two low Σ favored GBs display significantly weak trapping effect, which is consistent with the formation energy distribution. The reduction in the migration barrier has been observed due to the decrease of distance from the GB center. Furthermore, the barriers of migration towards the GB are lower than the barriers of migration away from the GB. As evident by NEB calculation, absorption sink effect of GB has been observed. This effect saturates as the distance reaches 8 Å or more. Our simulation results provide an insight into the GB trapping effect in alpha-Fe.

Highlights

Structural materials in the nuclear industry are polycrystalline materials having preexistent structural impurities
The basic concept is that a grain boundary (GB) can be designated as a combination of building blocks or structural units (SUs), and the combination and sequence of the SUs are representative for the GB properties
The structure of 9{221} GB is composed of both “A” and “B” SUs in 2:1 ratio, which can be described as |AAB.AAB|

Summary

Introduction

Structural materials in the nuclear industry are polycrystalline materials having preexistent structural impurities. Six symmetric tilt grain boundaries models (STGBs) are created to investigate the effect of the GB on the diffusion of P atom.

Results

Conclusion