Effect of H on the formation of vacancy dislocation loops in α-Fe

Molecular statics calculations and dynamics annealing relaxation were employed to calculate the formation and binding energies of vacancies and 3D vacancy or vacancy-hydrogen (H) clusters, as well as 2D vacancy or vacancy-H clusters on (111), (011) and (211) planes. Our calculations show that vacancies prefer to form 3D clusters and vacancy dislocation loops are difficult to form, while vacancy-H clusters prefer to shape into 2D clusters, especially on (211) planes.

Since H prefers the directional bonding, a va- cancy cluster with H atoms tend to form a vacancy dislocation loop with its slip direction along the 100 direction and on the (211) habit plane. Our results are consistent with the experimental observations, and provide a possible mechanism for the formation of vacancy dislocation loops in α-Fe. Furthermore, we have also explored how dislocation loops trap self-interstitial atoms, vacancies and H atoms.