Tensile Deformation of Zinc Bicrystals under Hydrostatic Pressure

Abstract

Tensile tests have been made on the bicrystal specimens of zinc under 1000kg/cm² hydrostatic pressure. Four different types of bicrystal specimens have been prepared. Each had a longitudinal grain boundary parallel to the tensile axis, and was composed of the two component grains of <1010> and <1120> as the tensile axis, respectively.
In the bicrystals the {1122} <1123> pyramidal slips accelerate the twin nucleation. The stress required to make this twin nucleated spread over the whole specimen is smaller than that required to initiate the twin nucleation and is much smaller when strain difference between the two twinned grains is larger. Once the twin had spread over the specimen, the deformation of the specimen proceeds in such mechanism as the pyramidal slip within the twins for the <1010> crystal, and the basal slip within the twins for the <1120> crystal. Thus, there is a large flow stress difference between the component crystals. The stress-strain curve of a bicrystal is well consistent with the mean curve of the component crystals, showing that the grain boundary had little effect on the stress-strain relationship. Microscopic observation of the deformed specimen shows that the compatibility requirements in the vicinity of the grain boundary should be satisfied by such factors as the basal and pyramidal slips in the matrix and twins, the kinks, the twins having small orientation factor and the secondary twins within the twins.