Kirch, D: In-Situ SEM Investigation of Individual and Connec

boundaries, the majority of grain boundary systems were found to be controlled by the lower mobility of the curved grain boundaries. The only exception was found during investigation of the grain boundary system TJ-twist-19 revealing a system migration influenced by the triple junction mobility at all investigated temperatures, confirming the existence of a finite triple junction mobility and its dependence on triple junction crystallography. However, the boundary system TJ-twist-19 was not found to change its state of motion as observed for sample TJ-41. Aluminum bicrystal samples, containing individual <100> and <111>tilt grain boundaries, were investigated experimentally in-situ in a temperature range between 300C and 640C for a range of boundary misorientations. The study revealed, for both systems, a different behavior of SAGBs in contrast to LAGBs. Grain boundaries with a rotation angle below 15 were found to be immobile during annealing at a given temperature in conjunction with a faceted grain boundary shape. Owing to grain boundary anisotropy the boundary facets correspond to boundary inclinations which possess a particularly low energy as confirmed by additional MS-simulation studies on bicrystals with equivalent crystallography. In contrast, LAGBs with a misorientation angle larger than 15 did not tend to form grain boundary facets. Instead, the grain boundaries assumed a curved shape and moved in steady-state in the entire investigated temperature range, as expected for curvature driven grain boundary motion assuming grain boundary isotropy. The microstructure evolution of individual circular grains in thecourse of grain shrinkage was simulated for bicrystals implementing a 2D-vertex model. The study revealed that the modeled grain shape is consistent with the experimentally observed boundary shape in bicrystal samples with equivalent crystallography. Furthermore, the study revealed that grain boundary anisotropy can affect the rate of grain area change. In the case of grains with a pronounced grain boundary anisotropy, a preferred formation of straight facets composed of low energy boundary planes was observed. As a result, the mean free energy of the grain boundary was reduced, causing a decrease of the capillary driving force. Owing to the decrease of P, the normal velocity of the respective segments decreased likewise, causing a retardation of grain shrinkage. Finally, the author believes that the results of the studies presented here lead to a better understanding of solitary and connected grain boundaries and their role in modern materials science and engineering.