Diffusion of hydrogen within idealised grains of bcc-Fe: A kinetic Monte Carlo study

TL;DR

This study uses kinetic Monte Carlo simulations with first-principles data to analyze hydrogen diffusion in bcc iron microstructures, revealing complex concentration-dependent behavior and reduced diffusivity near interfaces.

Contribution

It introduces a detailed kMC model for hydrogen diffusion in bcc-Fe based on first-principles data, providing new insights into microstructure effects.

Findings

Hydrogen diffuses mainly within interface regions.

Diffusivity is lower in microstructures than in pure bcc-Fe.

Diffusion coefficient decreases with increasing hydrogen concentration.

Abstract

Structural defects in materials such as vacancies, grain boundaries, and dislocations may trap hydrogen and a local accumulation of hydrogen at these defects can lead to the degradation of the materials properties. An important aspect in obtaining insight into hydrogen induced embrittlement on the atomistic level is to understand the diffusion of hydrogen in these materials. In our study we employ kinetic Monte Carlo (kMC) simulations to investigate hydrogen diffusion in bcc iron within different microstructures. All input data to the kMC model, such as available sites, solution energies, and diffusion barriers are obtained from first-principles calculations. We find that hydrogen mainly diffuses within the interface region with an overall diffusivity that is lower than in pure bcc-Fe bulk. The concentration dependence of the diffusion coefficient is strongly non-linear and the diffusion coefficient may even decrease with increasing hydrogen concentration. To describe the macroscopic diffusion coefficient we derive an analytic expression as a function of hydrogen concentration and temperature which is in excellent agreement with our numerical results for idealised microstructures.