Dresden 2011 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 28: Topical Session Electron Theory III

MM 28.4: Talk

Wednesday, March 16, 2011, 16:45–17:00, IFW A

First-principles simulations of H interstitials within Σ 3 and Σ 5 grain boundaries in bcc Fe — •Yaojun Du, Jutta Rogal, and Ralf Drautz — ICAMS, Ruhr-Universität, Bochum, Germany

Hydrogen impurities in steels can degrade the mechanical properties of the host material. Due to the complex nature of hydrogen-embrittlement (HE), the underlying HE mechanism has not been fully understood. One possible cause is that H impurities may weaken the bonding of Fe atoms near the grain boundaries, leading to an embrittlement of the bulk material. In this work, we study the interaction of H interstitials with Σ 3 and Σ 5 grain boundaries (GBs) in bcc Fe, and investigate the migration processes of H within the GBs, using density functional theory. Our results indicate that the GBs that we studied provide energy traps of 0.4-0.5 eV for H interstitials, and these trapped H interstitials may facilitate the crack growth at the GB interface. For the Σ 5 bcc Fe GB we find that the fast diffusing H within Fe bulk region can be readily trapped to the GB interface with an escape barrier of 0.6 eV. On the other hand, the trapped H interstitial can perform a relatively slow migration within the interface with a diffusion barrier of 0.25 eV. We are now carefully computing the transition rates among inequivalent H sites within the Σ 5 bcc Fe GB. These results will serve as input for a lattice kinetic Monte Carlo model to study the dynamics of H diffusion in the vicinity of the GB.