Grain boundary migration and it's mechanism of Fe-3wt%Si solid solution bicrystals

The migration kinetics of the (221)Σ9 coincidence and random grain boundaries in Fe-3wt%Si solid solution bicrystals was experimentally studied at temperatures between 1200 and 1625K by a capillary technique. The driving force and the mobility for the grain boundary migration was calculated from the experimental results. On the basis of the calculations, the mechanism of grain boundary migration was discussed. There are two different mechanisms of the grain boundary migration for both the grain boundaries depending on the annealing temperature and the driving force. At lower temperatures, the migrating rate is small and the mobility is about 4 times larger for the (221)Σ9 grain boundary than the random grain boundary. At these temperatures, the activation energies of the grain boundary migration for both the grain boundaries are almost the same and coincide with that of the intrinsic diffusion of Si in αFe. Thus, the rate controlling process of the grain boundary migration seems to be the dragging of solute atmosphere formed along the migrating grain boundary. On the other hand, at higher temperatures, the migrating velocity is large and the mobility is greater for the random grain boundary than for the (221) Σ9 grain boundary. The activation energies of the grain boundary migration for both the grain boundaries are about 3/4 of those of the self diffusion in αFe. Therefore, the grain boundary migration at these temperatures is considered to be controlled by the grain boundary diffusion. The transition temperature between the two different mechanisms decreases with increasing driving force. This may be due to breaking away from the solute atmosphere for the migrating grain boundary.