ABSTRACTStress induced migration of tilt grain boundaries with misorientation angles 13.5°, 57.5° and 70.4° in high-purity Cu bicrystals was investigated by in situ observations in a scanning electron microscope. The investigated boundaries moved steadily under the applied stress at a given temperature and produced shear parallel to the boundary plane. The measured coupling factors, i.e. the ratios of normal boundary displacement and lateral grain translation are in good agreement with predictions from a geometric model. Grain boundary migration was investigated in the temperature regime between 600°C and 800°C and the corresponding migration activation parameters were determined. The considerably different values of the migration activation enthalpy (in the range between 0.71 and 1.21 eV) revealed that the mobility of tilt boundaries in Cu depends on the misorientation angle, i.e. on the grain boundary geometry.