PNNL

Abstract

Formation energies, binding energies, and migration energies of interstitial He atoms in and near the core of an a/2 screw dislocation in alpha-Fe are determined in atomistic simulations using conjugate gradient relaxation and the Dimer method for determining saddle point energies. Results are compared as a function of the proximity of the He to the dislocation core and the excess interstitial volume in regions around the dislocation. Interstitial He atoms have binding energies to the screw dislocation that are about half the magnitude of binding energies to the a/2{110} edge dislocation in alpha-Fe. Migration energies of interstitial He atoms for diffusion toward the dislocation and for pipe diffusion along the dislocation are about the same magnitude for the screw and edge dislocations, despite a significant difference in their migration mechanisms. Interstitial He atoms diffuse along the dislocation cores with a migration energy of 0.4-0.5 eV