PNNL

Abstract

Migration energies of vacancies and He atoms in and near the core of an a/2 screw dislocation in a-Fe were determined in atomistic simulations using conjugate gradient relaxation and the Dimer method for determining saddle point energies. Results for defects in initial positions in and near the screw dislocation core were obtained for migration toward and away from the dislocation line, as well as along the dislocation line direction. For both vacancies and individual interstitial helium atoms migration is favored toward and along the screw dislocation. Vacancies trapped in the dislocation core migrate along the dislocation with a migration energy of about 0.4 eV, which is about half the migration energy of vacancies in the perfect crystal.