Atomistic study of hydrogen diffusion in presence of defects in bcc and fcc iron

We present classical atomistic study of hydrogen diffusion in a-Fe and y-Fe in presence of grain boundaries, surfaces or vacancies. Being pronounced traps for hydrogen, defects of different complexion play an important role in diffusion mechanisms related to hydrogen embrittlement. Clarification of hydrogen interaction with isolated defects is a necessary step towards establishing the hierarchy of related diffusion coefficients. We estimated possible impact of the above-mentioned defects on the H diffusion using recently developed interatomic potential capable of simulations of a and y Fe phases. From the classical simulations we found that H interplay with defects may strongly depend on the host Fe structure: in fcc Fe, grain boundaries and surfaces provide accelerating path for diffusion, while in bcc we see no such effect. In case of a mono-vacancy, binding with hydrogen leads to reduction in a vacancy migration rate for both lattice types. However atomistic mechanisms of such slow-down are different. For bcc Fe we also estimated equilibrium hydrogen concentrations at grain boundaries and discuss a role of hydrogen located in GBs in overall hydrogen flux in polycrystal.