The dimer method for searching transition states has been used to systematically study possible migration paths of vacancies, He interstitials and He-vacancy (He/V) clusters at ?11 {323} and ?3 {111} grain boundaries (GBs) in ?-Fe. Vacancies trapped at the GBs diffuse along the GBs with migration energies much less than that within the perfect crystal. Long-time dynamics simulations of diffusion pathways reveal that vacancies migrate one-dimensionally along the close-packed rows in the ?3 GB, and one-dimensionally in zigzag paths within the ?11 GB. Also, dimer saddle point searches show that He interstitials can diffuse along the GBs with migration energies of 0.4-0.5 eV, similar to those of individual vacancies at the GBs, and the corresponding mechanisms are determined. The rate-controlling activation energy for migration of a He-divacancy cluster in the GBs determined using the dimer method is about 0.9 eV, which is comparable to the migration energy for a He-divacancy cluster in bulk ?-Fe.
Revised: September 28, 2016 |
Published: March 1, 2008
Citation
Gao F., H.L. Heinisch, and R.J. Kurtz. 2008.MIGRATION OF VACANCIES, HE INTERSTITIALS AND HE-VACANCY CLUSTERS AT GRAIN BOUNDARIES IN ALPHA-FE. In Fusion Materials Semiannual Progress Report for the period Ending December 31, 2007, edited by GR Nardella. 186-191. DOE/ER-313/43. Oak Ridge, Tennessee:Oak Ridge National Laboratory.PNNL-SA-58951.