Effects of strain and defects on hydrogen diffusion and trapping in a-iron using a developed Fe-H reactive force field

XL Jiang and CW Yang and XL Wang, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 58, 210-222 (2024).

DOI: 10.1016/j.ijhydene.2024.01.181

Strain and defects significantly affect the diffusion and trapping of hydrogen (H), which plays a critical role in the initiation of hydrogen embrittlement phenomena in a -iron. In this work, based on a newly developed Fe -H reactive force field, the molecular dynamic models with perfect lattice and defects across various strain regions are presented for studying diffusion and aggregation of H atoms in a -iron. At first, the effect of gradient strain on H diffusion and trapping are elucidated. Then, H diffusion and trapping behaviors at defects (including vacancies, edge dislocations, E3110(112) and E5001(310) grain boundaries) undergoing various strain are investigated. The simulation results demonstrate that the gradient strain leads to a gradient distribution of H solution energies, which drives a directional diffusion and aggregation of H atoms from compressive to tensile strain region. The charge transfer from nearest neighbor Fe atoms to H atoms weakens the Fe -Fe interactions, consequently resulting in the local stress relaxation within the H -enrich region. Regarding the H diffusion and trapping at defects, the results show that tensile strain decreases the difference in H solution energies between the bulk structure and defects, which facilitates H diffusion and escape. Conversely, compressive strain amplifies the energy difference, leading to the enhancement of H trapping and inhibition of H transport. This study contributes to an enhanced comprehension of interactions between hydrogen and defects under strain from an atomic scale.

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