Molecular dynamics simulation of hydrogen atom diffusion in crystal lattice of fcc metalsThe study of diffusion of hydrogen atoms in the crystal lattice of fcc metals Pd, Ni, Al, Ag was performed by the method of molecular dynamics. The diffusion characteristics of hydrogen impurity (activation energy of hydrogen atom migration and pre-exponential factor in the Arrhenius equation) in the considered metals were calculated. It is shown that the prevailing mechanism of the over-barrier hydrogen diffusion in fcc metals consists of successive migration through octahedral and tetrahedral pores. During migration, as a rule, the hydrogen atom is not delayed in tetrahedral pores.Keywords: Molecular dynamics; Metal; Hydrogen; Diffusion; Diffusion mechanism
IntroductionThe interaction of hydrogen with metals has been the subject of intensive study over the last century. On the one hand, this is due to the practical interest in using the metal-hydrogen system: creation of radiation-resistant materials, filters for obtaining of pure hydrogen, including for isotope separation, accumulation and storage of light gases in metals and alloys and the problem of hydrogen transportation. On the other hand, this is due to the undesirable effects of hydrogen on the properties of materials (embrittlement, corrosion, cracks spreading) [1,2].Hydrogen atoms have a unique small mass and size in comparison with other interstitial atoms in metals, and for this reason have extremely high diffusion mobility [3,4]. The diffusion coefficients of hydrogen in solid metals are almost the same as in liquids. This feature, in addition to the small size and mass of the hydrogen atom, is also associated with the dissociation of a hydrogen molecule into individual atoms upon ingress into the metal [5,6]. In metal crystals, hydrogen atoms are in interstitials and in the diffusion process they pass from one interstitial site to another. In fcc lattice, hydrogen can occupy two types of interstitial sites: octahedral and tetrahedral. At the present time, the question of the mechanism of hydrogen diffusion in the crystal lattice of metals remains. Even in a pure crystal, transitions between interstitials of different types are possible, which entails, in particular, the ambiguity of the activation energy of hydrogen diffusion. In addition, as noted in [7], the redistribution of hydrogen atoms in interstitial sites of various types due to changes in external conditions, for example, deformation, can lead to a change in the diffusion parameters. It should be noted that other factors may also lead to deviations from the Arrhenius law, in particular, the possibility of diffusion jumps of different lengths and the effect of crystal lattice defects [1,5].The aim of the present work is to study the mechanism of hydrogen atom diffusion in the crystal lattice of fcc metals using the molecular dynamics method and to calculate the diffusion parameters: the activation energy and the pre-exponential factor in the corresponding Arrhenius equation. Typical fcc metals with d...
