Kinetics of grain boundary migration in copper bicrystals with [001] rotation axes

Abstract

Kinetics of grain boundary migration in high-purity copper bicrystals with common [001] rotation axes have been investigated as a function of driving force, angle of misorientation and temperature. In all cases, grain boundary displacements obey a parabolic rate law and concomitant velocities are linearly related to driving force implying that intrinsic mobilities have been measured. Migration of low-angle boundaries is characterized by an activation energy of 49 kcal/mole. Close agreement between this value and 47 kcal/mole for lattice self diffusion in copper indicates that motion of low-angle boundaries is controlled by dislocation climb via a lattice self-diffusion mechanism. Migration of random high-angle boundaries, on the other hand, is characterized by activation energies ranging from 26 to 30 kcal/mole indicating that motion is controlled by direct atom transfer across the boundary. For a given misorientation, it has been possible to study boundary migration either in a pure tilt configuration or with varying degrees of twist character merely by varying orientation of the [001] rotation axes relative to the specimen surfaces. It is observed that values of the critical misorientation for transition from low to high-angle migration kinetics are about 9° and 13° for mixed and pure tilt boundaries respectively. Differences in mobility occur between the two configurations even at large misorientations, presumably due to the anisotropic nature of boundary diffusion.