Modeling of He-bubble migration in bcc Fe

Kinetic Monte-Carlo simulations were performed to investigate the migration of He-bubbles in bcc Fe, using the binding energies of point defects to a He-bubble and the migration energies of an Fe atom on bubble surface, both of which are obtained by molecular dynamics and molecular static calculations. This approach linking multiple simulation methods can remove the degrees of freedom for lattice vibrations effectively and enables us to perform long time scale simulations successfully. When the equilibrium concentration of point defects in a matrix is assumed, a He-bubble can migrate by the surface diffusion mechanism and show the Brownian motion. The diffusion coefficient of larger He-bubbles than about 0.8 nm in diameter is proportional to d−4, where d is bubble diameter. It is in good agreement with conventional continuum theory predictions.