Effect of hydrogen on vacancy diffusion

Abstract

Although it is widely recognized that even small amounts of hydrogen (H) can cause embrittlement in iron (Fe) and in (high-strength) steels, the fundamental mechanisms that cause it are not yet completely understood. To contribute to a better understanding of the behavior of H in metals, we use parallel replica dynamics (PRD) to study the effect that different amounts of atomic H have in the diffusion of a single vacancy in body-centered cubic (BCC) Fe. Using PRD we calculate the diffusion of H-vacancy complexes at temperatures and timescales that are not reachable using classical methods. Additionally, based on the PRD results and calculations of the minimum energy paths of migration, we propose a mechanism for the migration of vacancy-H complexes and formulate an analytical model for the calculation of their joint diffusivity.