Grain boundary migration in Fe-3%Si

Grain boundary (GB) migration was studied on Fe-3%Si bicrystals, using both the reversed-capillary technique and the method of constant driving force. The reduced mobility of the completely dragged motion was determined using the reversed-capillary geometry with samples of commercially pure material. On high purify Fe-3.5%Si bicrystals with [001] tilt boundaries with different angles the reduced mobility of the free moving boundary was determined in the temperature range from 944 degrees C to 1104 degrees C, using in most cases the constant driving force technique. In-situ observation of the fastest migrating boundary confirmed the results obtained by conventional methods. For the free motion the activation enthalpy and the pre-exponential factor of the reduced mobility were determined for the different types of tilt boundaries studied. Activation enthalpy and logarithm of the pre-exponential factor are linearly related, i.e. comply with the compensation effect. The obtained results were in good accordance with literature data of GB mobility in Fe-3%Si bicrystals. From the measured values and the literature data a compensation temperature of 1113 degrees C +/- 50 degrees was found, i.e, slightly below the eutectic temperature of 1200 degrees C of the system Fe-Si. For the reversed-capillary technique experimentally observed shapes of the moving GB were compared to theoretically predicted shapes. It was found that a better fit is obtained when taking into account the drag effect by impurities. It was shown that owing to this drag effect for the reversed-capillary technique, contrary to the constant driving force technique, a scaling behavior of the shape of the boundary in the course of migration is impossible. Thus displacement-independent geometry factors used for calculation of the mobility can only be approximations in the case of a free motion.