Grain Boundary Migration in Fe-Si Alloy Bicrystals

Abstract

Migrations of tilt boundaries in Fe - Si alloy bicrystals have been investigated by Sun and Bauer technique as a function of misorientation angle, driving force, temperature and Si content. Two distinct regions with different migration behaviour are observed on temperature -dependence of mobility: a drastic change in mobility occurs at a critical temperature. The critical temperature depends on the driving force and also the grain boundary (GB) character. The activation energy for grain boundary migration (GBM) is ca. 2/3 of that for Fe bulk self - diffusion in the higher temperature region, suggesting that the boundary motion is governed by GB diffusion. On the other hand, the activation energy increases up to ca. 220 kJ/mol in the lower temperature region, being in agreement with that for Si intrinsic - diffusion in α-Fe. This agreement shows that GB is most likely to move dragging Si atmosphere. Also, it is of great interest that the mobility for coincidence boundary, particularly Σ9 GB, is higher than that for a random boundary in the lower temperature region, but reverse is the case in the higher temperature region. In addition, the mobility depends on Si content in the lower temperature region; it increases with decreasing Si content, whereas such dependence is scarcely observed in the higher temperature region. These results obtained here will be discussed from the viewpoint of the interaction between GB and solute atoms.