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Abstract

In this study, multi-phase field and molecular dynamics simulations have been applied to study grain growth mechanisms on the nanoscale.

In molecular dynamics simulations we study directly the shrinkage of a small spherical grain, embedded in a single crystal, thus eliminating effects of triple lines and focusing on the pure grain boundary mobility. For nanometer size grains we observe a constant grain boundary velocity, independent of the radius of curvature of the grain boundary. The activation energy of grain boundary motion in this regime is determined to be on the order of one tenth of the self diffusion activation energy, which is consistent with experimental data. Furthermore, we calculated the evolution of mechanical stresses (Laplace pressure) during the shrinkage and the concentration of vacancies that result from the release of grain boundary free volume into the bulk caused by the reduction of grain boundary area.

Based on these observation a model for grain growth on the mesoscopic scale is developed considering reduction of interface area, vacancy diffusion and stress due to the rearrangement of the defect distribution into account.

The combination of both approaches leads to a consistent picture of the interplay of short range diffusion and long range stress effects which explains the linear grain growth in the nano regime and the transition to normal grain growth at elevated temperatures.