Grain size influence for the Hydrogen Diffusion in bcc Fe

RAMUNNI, V.P.; M. I. PASCUET; N. CASTIN; A.M. F. RIVAS

Cordoba

Congreso; AFA 2021; 2021

We have performed numeri al al ulations in order to study the diusion ofHydrogen (H) in bcc Fe, ontaining a high-angle symmetri tilt grain boundary (GB), as a fun tion of both the temperature and the average grain size. For this purpose, we have developed a mi ros opi ee tive model whi h in ludes diusion in the bulk as well as in the GB, thus in orporating the grain size. Our model distinguishes between diusion along the GB, in parallel with the bulk, while diusion through the GB is to be onsidered in series. The bounding and migration energies of the H interstitial sites needed in the model are obtained through an extensive study of H dissolved in a high-angle symmetri tilt GB.This is undertaken in the framework of a set of lassi al interatomi potentials, and partially from Density Fun tional Theory (DFT) al ulations, in order to he k the onsisten y of stru tures. We nd that preferential trapping sites for H in the grain boundary, delays the H migration enhan ing its solubility. Our results for H diusion oe ients are in agreement with the available experimen tal data, however various kinds of GBs are present in real samples. In addition, we see that for high temperatures, H diusion does not depend on the grain size, obtaining similar results than in bulk. Whereas for room temperatures (290K) and nano-sized grains (100 nm) the diusion an slow down up to two orders of magnitude.