Ab initio modelling of the interaction of H interstitials with grain boundaries in bcc Fe

Hydrogen that is accumulated within the grain boundaries can lead to a decrease of the critical strain required to fracture the material. The paper presents results of ab initio modelling of hydrogen-grain boundary interaction in ferromagnetic bcc iron. Modelling was performed using density functional theory with generalised gradient approximation (GGA'96), as implemented in WIEN2k package. Three fully relaxed tilt grain boundaries, Sigma 5(310), Sigma 5(210) and Sigma 3(111), were studied. The supercells contained 40-48 atoms, i.e. 20-24 atoms in each of the two 'grains'. Calculated formation energies of grain boundaries is 1.44, 1.83 and 1.46 J/m(2) and the maximum binding (trapping) energies of hydrogen to the boundaries are 0.43, 0.83 and 0.39 eV, respectively. These values are close to other researchers' data. The higher value of trapping energy of the Sigma 5(210) boundary is probably due to the asymmetrical atom configurations resulting frommutual rigid shift of the two grains that was necessary to be introduced to provide optimal distances between Fe atoms, unlike the other two boundary types. [GRAPHICS] .