True absolute grain boundary mobility : Motion of specific planar boundaries in bi-bicrystals under magnetic driving forces

The migration of planar 90 deg < 112 > tilt grain boundaries with the same misorientation but different boundary inclination in Bi-bicrystals was investigated. The driving force for grain boundary motion was created by the action of a magnetic field on bicrystals of bismuth, which is magnetically anisotropic with different susceptibilities parallel and perpendicular to the trigonal axis. The driving force dependency of boundary velocity was measured and the absolute value of grain boundary mobility was determined. The grain boundary mobility was found to strongly depend on grain boundary inclination. The mobility parameters (activation enthalpy and preexponential factor) for a symmetrical 90 deg < 112 > tilt grain boundary were much smaller than for an asymmetrical ( psi =45 deg ) boundary. The mobility of the asymmetrical grain boundary depended on the direction of motion. For the given crystallography the boundary moved faster, if the trigonal axis in the growing grain was parallel rather than perpendicular to the direction of motion.