On the mechanisms of grain boundary migration

The motion of planar, symmetrical <112>- and <111>-tilt boundaries under the influence of a mechanical shear stress was investigated and compared with experiments on curved, symmetrical <112>- and <111>-tilt boundaries with the same angles of misorientation under the influence of a constant capillary force. It was found that the motion of planar low angle grain boundaries as well as planar high angle boundaries can be induced by the imposed external stress and that the dependence of the activation enthalpies for grain boundary motion on the misorientation angle is different for planar and curved <111>-grain boundaries. The different observed activation enthalpies are attributed to different migration mechanisms for grain boundary motion. It seems that the activation of a migration mechanism depends on the misorientation angle and the driving force and that grain boundaries have the possibility to move by different migration mechanisms. Irrespective of whether grain boundaries are planar or curved there was a distinct transition between low angle and high angle grain boundaries at the same misorientation angle.