Atomistic investigation of hydrogen embrittlement effect for symmetric and asymmetric grain boundary structures of bcc Fe

L Fu and HY Fang, COMPUTATIONAL MATERIALS SCIENCE, 158, 58-64 (2019).

DOI: 10.1016/j.commatsci.2018.09.038

An atomistic simulation study has been carried out to understand that the grain boundary hydrogen (H) will have a significant effect on grain boundary (GB) energy, surface (FS) energy and cohesive energy. Molecular statics simulations at zero temperature for pure a-Fe with a single H atom and two H atoms placed at the crystal interfaces of <1 0 0> symmetric tilt grain boundary (STGB) systems and asymmetric tilt grain boundary (ATGB) systems were performed. Simulation results show that the segregation energy of solute H atom on the GB was greater than zero, i.e. the system energy with H located at the GB is larger than the energy with H at the free surface, which implies that the failure mode should be intergranular. Moreover, only when H is located within the distance of 2 a (lattice constant) from the grain boundary will H have a significant effect on grain boundary destruction. Finally, the calculated GB energy, surface energy and cohesive energy of bcc Fe <1 0 0> STGB and ATGB systems are affected by the hydrogen segregation at the GB structure. Both the surface energy and the grain boundary cohesive energy decrease with the increase of hydrogen coverage. The impacts of H or 2H atoms at the GB plane on the surface energy and the cohesive energy are explored as quadratic polynomial functions. The promoting effect of 2H atoms on the intergranular fracture is more obvious than H atoms'. Both H and 2H have more effect on surface energy than cohesive energy.

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