  This work presents a multiscale and multiphysics framework to investigate the
radiation-induced damage in nano-crystalline materials. The framework combines
two methodologies, including molecular dynamics simulations with electronic
effects and long-term atomistic diffusion simulations in nano-crystalline
materials. Using this framework, we investigated nano-crystalline materials'
self-healing behavior under radiation events. We found that the number of
defects generated in nano-crystals during the cascade simulations was less than
in single crystals. This behavior was due to the fast absorption of
interstitial atoms in the grain boundary network during the cascade
simulations, while vacancies migrated to the boundaries in a much longer time
scale than interstitial atoms. Thus, nano-crystalline materials showed a
self-healing behavior where the number and size of the defects are drastically
reduced with time. We found that the self-healing behavior of nano-crystalline
materials is limited, and about 50% of vacancies survived. This effect resulted
from clusters of vacancies' collective behavior, which are much more stable
than individual vacancies.
