On Crack Nucleation in Zinc upon Interaction of Basal and Pyramidal Dislocations

The interaction of intersecting basal and pyramidal dislocation pileups in single-crystal zinc has been analyzed. Different versions of the formation of sessile (1/3[4 (2) over bar(2) over bar3]) and cleavage ([0001]) dislocations (microcrack nuclei) are considered. The merging of the head dislocations in pyramidal pileups is shown to be preferred. The conditions for thermally activated dislocation merging are derived. The conditions for crack opening according to the Gilman-Rozhanski. mechanism are discussed. It is analytically established that the breaking stress, normal to the (0001) plane in the region of microcrack nucleation, exceeds the theoretical strength.