“Pure” Grain-Boundary Sliding in Zinc Bicrystals

Abstract

Bicrystals of zinc containing basal tilt boundaries of controlled orientation have been tested in simple shear over the range 320–390° C. Rapid grain-boundary sliding was observed in the absence of macroscopic trans crystalline slip. This “pure” grain-boundary sliding was accompanied by the emission of dislocations from the sliding boundaries and the creation of substructure in the crystalline regions adjacent to the boundaries. Grain-boundary slide-hardening was often noted in the absence of observable grain-boundary cusps or irregularities. By assuming a sliding-rate law of the form έ = Aσⁿ t ^(m−1) exp( − Q_s/KT) and by using differential test methods, values were obtained for the apparent activation energy (Q_s ) and the stress parameter (n) for the “pure” grain-boundary sliding. The values Q_s = 31 ± 5 (kcal/mole) and n = 4.5 ± 1.8 give strong support to the general conclusion that “pure” grain-boundary sliding is controlled by the case with which dislocations can be emitted by a sliding boundary and subsequently pass through the crystalline regions adjacent to the grain boundary.