GRAIN BOUNDARY SEGREGATION OF HYDROGEN IN BCC IRON: ELECTRONIC STRUCTURE

Abstract

The electronic properties of H impurity in an Fe Σ = 5, 53.1° [100] (012) symmetrical tilt grain boundary (GB) were studied using qualitative electronic structure calculations in the framework of the atom superposition and electron delocalization molecular orbital (ASED-MO) theory. A large cluster containing 197 Fe atoms was used to simulate the local environment of the boundary. The most stable positions for one H atom and two H atoms at the GB core were determined. The total energy of the cluster decreases when the H atoms are at that location, making it a possible site for H accumulation. The binding energy found was less than that of a Σ = 5 [100] (013) GB. An analysis of the orbital interaction reveals that H–Fe bonding involves mainly the Fe 4s and H 1s orbitals. A higher contribution of d orbitals is present, which show a different behavior when compared with mixed dislocation and vacancy in the bulk Fe. The interatomic bonding along the Fe atom chains via H atoms is very inefficient, thus resulting in significant weakening of the interatomic bonding. H–H interaction was also analyzed.