25th IAEA Fusion Energy Conference - IAEA CN-221

Energetic, Crystallographic and Diffusion Characteristics of Hydrogen Isotopes in Iron

17 Oct 2014, 08:30

4h

Green 8-9 (Hotel Park Inn Pribaltiyskaya)

Poster Poster 7

Speaker

Dr Alexander Sivak (NRC "Kurchatov institute")

Description

Energetic and crystallographic characteristics of various interstitial configurations of H atoms and their complexes with self-point defects (SIA – self-interstitial atom, vacancy) in bcc Fe have been calculated by molecular statics using Fe-H interatomic interaction potential developed by A. Ramasubramaniam et al. (Phys. Rev. B 79 (2009) 174101) and modified here and Fe-Fe matrix potential M07 developed by L. Malerba et al. (J. Nucl. Mater. 406 (2010) 19). The most energetically favorable configuration of an interstitial H atom is tetrahedral configuration. The height of the energy barrier for H atom migration is 0.04 eV. H atom in the substitution position is unstable and shifts in the direction of the nearest octopore during the relaxation process staying at a distance of 0.024 nm from it. The resulting configuration has the highest binding energy of all the considered complexes “vacancy – H atom” (0.54 eV). The energy barriers for the jump of H atom from a vacancy to the nearest tetrapore and back are 0.47 eV and 0.05 eV, respectively. The binding energy of the most energetically favorable configuration of the considered complexes “SIA – H atom” equals 0.15 eV. The interaction energy of H atom with a SIA decreases with distance slower than in the case of interaction with a vacancy. The binding energy of H atom with an edge dislocation in <100>{001} slip system is 0.49 eV. The binding energies of complexes “vacancy – n H atoms” (n = 1, ..., 15) have been calculated. The binding energy of H atom with the complex decreases from 0.54 eV to 0.35 eV with increasing of n from 1 to 6. The value of binding energy decreases sharply to ~0.1 eV at n > 6. One vacancy can contain up to 6 H atoms. Adding of the seventh H atom leads to the expulsion of one of the other six H atoms from the vacancy. The temperature dependences of hydrogen isotopes diffusivities (D^H, D^D, D^T) in Fe have been calculated for the temperature range 70 – 1100 K using molecular dynamics. The temperature dependencies of D^H, D^D, D^T have a parabolic form at temperatures higher than 300 K. The values of D^H, D^D, D^T are almost the same at 300 K. The isotope effect becomes stronger at higher temperature, e.g., ratios D^H/D^D and D^H/D^T at 1100 K equal 1.2 and 1.3, respectively.

Presentation materials

summary

MPT_P7-33.pptx