We simulate diffusion of point defects - vacancies, interstitials, substitutional defects - in polycrystals on an atomistic (using molecular dynamics) and mesoscopic levels. By mesoscopic simulations, we can take into account the difference in diffusion coefficients inside a grain and within the grain boundaries and also the partial absorption of defects on these boundaries. Such simulations allow to explore the role of the polycrystallinity and the influence of grain interfaces on the diffusion kinetics and the equilibrium distribution of point defects in crystals.
Solving mesoscopic equations of the dislocation dynamics, we model the dislocation motion in mono- and polycrystals. In these our simulations, we take into account not only the influence of external stresses, but also the long-range elastic interaction between the dislocations, formation of dislocation dipoles and dislocation annihilation. The influence of the grain boundaries in polycrystals as partial dislocation absorbers is also included into the model.
Integration of the equations of motion for dislocations over a sufficiently long time allows us to obtain their equilibrium distribution patterns, which can be directly compared to experimental images. Our results allow for the natural explanation of very different dislocation densities in various grains of an otherwise macroscopically homogeneous crystals, significant spatial fluctuations of the dislocation density within a single grain and formation of typical dislocation cell patterns