Diffusion coefficient of hydrogen interstitial atom in α-Fe, γ-Fe and ε-Fe crystals by first-principle calculations

The hydrogen diffusion process is a crucial issue related to hydrogen embrittlement. In this work, first-principle calculations were performed to investigate the diffusion behavior of hydrogen atoms in different Fe crystalline lattices. The hydrogen atom diffused in bcc Fe crystal through migrating from tetrahedral interstice to its nearest tetrahedral site; hydrogen atom diffused in fcc Fe along octahedral site-tetrahedral site-octahedral site; the diffusion path of the hydrogen atom in hcp Fe was from an octahedral site to its nearest octahedral site. The order of the diffusion coefficients of the hydrogen in the three crystal structures was D-bcc = 1.379 x 10(-4) cm(2)/s exp (-1120/T) > Df(cc) = 3.22 x 10(-4) cm(2)/s exp (-8425/T) > D-hcp = 6.161 x 10(-4) cm(2)/s exp (-8830/T). In addition, the diffusion behavior of a hydrogen atom near a vacancy was also investigated to determine the ability to trap a hydrogen atom in a vacancy defect in bcc-Fe and fcc-Fe, and the results indicated that hydrogen had higher mobility in the presence of a vacancy in the bcc Fe crystal. (C) 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.