Atomic-scale modeling of interactions of helium, vacancies and helium–vacancy clusters with screw dislocations in alpha-iron

Abstract

The interactions of He and vacancy defects with ⟨111⟩ screw dislocations in alpha-Fe were modeled using molecular statics, molecular dynamics and transition state energy determinations. The formation energies and binding energies of interstitial He atoms, vacancies and He–vacancy clusters near and within dislocations in alpha-Fe were determined at various locations relative to the dislocation core. Using the dimer transition state method, the migration energies and trajectories of the He and vacancy defects near and within the screw dislocation were also determined. Both interstitial He atoms and single vacancies are attracted to and trapped in the dislocation core region, and they both migrate along the dislocation line with a migration energy of about 0.4 eV, which is about half the migration energy of vacancies in the perfect crystal and about five times the migration energy for interstitial He in the perfect crystal. Divacancies and He–divacancy complexes have migration properties within the dislocation core that are similar to those in the perfect crystal, although the stability of these defects within the dislocation may be somewhat less than in the perfect crystal.