Grain boundary migration was studied, in Fe-3%Si bicrystals, by using the reversed-capillary technique and the method of constant driving force. The reduced mobility of the completely dragged motion was determined by using the reversed-capillary geometry, and samples of commercial purity. In high-purity Fe-3.5%Si bicrystals, with [001] tilt boundaries of various angles, the reduced mobility of the free-moving boundary was determined at 944 to 1104C by using mainly the constant driving force technique. The in situ observation of the fastest-migrating boundary confirmed the results which had been obtained by using conventional methods. In the case of free motion, the activation enthalpy and the pre-exponential factor for reduced mobility were determined for various types of tilt boundary. It was found that the activation enthalpy and the logarithm of the pre-exponential factor were linearly related (compensation effect). The results were in good agreement with published data on grain boundary mobility in Fe-3%Si bicrystals. Upon combining the present values with published data, a compensation temperature of 1113C was found. This was slightly below the eutectic temperature (1200C) of the system. In the case of the reversed-capillary technique, the experimentally observed shapes of the moving grain boundary were compared with the theoretically predicted shapes. It was found that a better fit was obtained upon taking account of the drag effect due to impurities. It was shown, due to this drag effect in the reversed-capillary technique, unlike the constant driving force technique, a scaling behavior of the shape of the boundary during migration was impossible. Therefore, the displacement-independent geometrical factors which were used for the calculation of the mobility could be only approximations in the case of free motion.

Grain Boundary Migration in Fe-3%Si. M.Furtkamp, G.Gottstein, D.A.Molodov, L.S.Shvindlerman: Materials Science Forum, 1999, 294-296, 501-4