Diffusion of Hydrogen into and through γ-Iron by Density Functional Theory

This study is concerned with the early stages of hydrogen embrittlement on an atomistic scale. We employed density functional theory to investigate hydrogen diffusion through the (100), (110) and (111) surfaces of γ-Fe. The preferred adsorption sites and respective energies for hydrogen adsorption were established for each plane, as well as a minimum energy pathway for diffusion. The H atoms adsorb on the (100), (110) and (111) surfaces with energies of ~4.06 eV, ~3.92 eV and ~4.05 eV, respectively. The barriers for bulk-like diffusion for the (100), (110) and (111) surfaces are ~0.6 eV, ~0.5 eV and ~0.7 eV, respectively. We compared these calculated barriers with previously obtained experimental data in an Arrhenius plot, which indicates good agreement between experimentally measured and theoretically predicted activation energies. Texturing austenitic steels such that the (111) surfaces of grains are preferentially exposed at the cleavage planes may be a possibility to reduce hydrogen embrittlement.