A study of deformation mechanisms of creep and superplasticity in zinc

Different types of zinc bicrystals were tested under creep conditions. Observations of grain boundary sliding along boundaries with different misorientations were made. It was established that Sigma = 9 coincidence boundary slides faster than boundaries of general type. Grain boundary sliding along coincidence boundary was activated at higher stress and only in the presence of intragranular slip. Sliding along coincidence and near-coincidence boundaries is accompanied by regular boundary migration whereas sliding along general boundary is not. The sliding-migration behavior of coincidence boundaries was explained in terms of DSC-dislocations associated with steps. Sliding along general boundaries was described in terms of non-DSC grain boundary dislocations having infinitesimal Burgers vector.;It is established in bicrystals with individual boundaries that crystallographic slip can increase significantly the rate of grain boundary sliding. Two mechanisms of stimulation of sliding by slip are proposed. Intragranular slip can make a direct contribution to grain boundary sliding in incompatible conditions of deformation. Identical deformation of grains can increase the rate of sliding only by its accommodation at boundary irregularities. The close relationship between sliding and slip at incompatible deformation makes intragranular slip strongly dependent on boundary structure and geometry of slip and independent of the Schmid factor.;It is demonstrated that deformation of textured fine-grained Zn-1.1%Al alloy in the direction favorable for intragranular slip decreases the contribution of grain boundary sliding to the total strain. Deformation in the direction unfavorable for slip increases its contribution. This shows that grain boundary sliding and intragranular slip are concurrent and independent processes during superplastic deformation.