Ab Initio Modelling of the Hydrogen Interaction with Ferrite/Cementite Interface

Abstract

The paper presents the results of ab initio modeling of the interaction of hydrogen atoms with ferrite/cementite interfaces in steels and thermodynamic assessment of the ability of interfaces to trap hydrogen atoms. For the first time the first-principle simulation of the interface between ferrite-cementite with the orientation relation of Isaychev type was carried out and the energy of the boundary formation was estimated. Using total energy calculations based on density functional theory implementing in package WIEN-2k the trapping energy of hydrogen with this interphase boundary was studied. The hydrogen atom was placed into eight non-equivalent positions on the interface between two phases, eight tetrapore sites in ferrite phase, and two octapore sites in cementite phase and total energy was calculated depending on its position. It is shown that the largest trapping energy (0,39 eV with zero-point energy correction) is provided by the location of hydrogen directly at the interface of the phases. It was founded that in the case of the strongest binding, a change occurs to the partial DoS at the nearest C atom neighbor. This indicates that the capture of hydrogen by the interphase boundary is associated with both an increase in free space and with the formation of a chemical bond with carbon atoms in the near environment.