Fiducial markers are generally employed to study the contribution of grain boundary sliding to the total creep strain.5 3 GBS leads to shearing of the fiducial markers and the shear offset provides a measure of the strain contri­bution. Since the stress concentrations developed during sliding are relieved by dislocation emission, dislocation activity can be expected in the vicinity of the grain boundary. Recent work by Gollapudi et al.51 shows increased dis­location activity close to the grain boundary during deformation controlled by GBS. At the same time, dislocations emitted from a grain boundary are expected to travel across the grain until they encounter a grain boundary. These dislocations subsequently pile up which is relieved by dislocation climb. Dislocation pile-up close to the grain boundary was also observed by Gollapudi et al.51 Figure 3.9a and 3.9b provide microstructural features associated with creep in the GBS regime.