Grain boundary sliding behavior was investigated on high-purity Zn bicrystals with special geometry, in order to examine critically the validity of McLean’s model which presumed grain boundary sliding to be brought about by climb-glide motion of slip dislocations along the grain boundary. Geometrical calculation based on this model leads to grain boundary sliding in the opposite direction to that of the resolved shear stress on the grain boundary plane at an angle of π/4 to the tensile axis, if an active slip plane intersecting the grain boundary is inclined by an angle θ(π⁄4<θ<π⁄2) to the tensile axis. Experimental results revealed that this prediction did not come true. This discrepancy can be solved, if one assumes a slip dislocation supplied from grain interior to grain boundary to dissociate into DSC dislocations which can climb-glide independently in the grain boundary to produce grain boundary sliding. Quantitative evaluation making use of the DSC dislocation model has successfully illustrated the characteristics of the grain boundary sliding rates.
