Modes of deformation under varied tensile directions in laminar, colloidal gold

Abstract

In perfect crystals of laminar colloidal gold, free from dislocations and stacking faults, the modes of deformation have been studied systematically, as a function of resolved shear stress or normal stress for each mode, using electron microscope and diffraction. The main modes of plastic deformation are cleavage crack, single glide and mechanical twinning. The cleavage crack is normally found under the tensile direction which gives the maximum normal stress to the cleavage surface. There is, however, another case of cleavage crack caused as a result of the glide deformation non-parallel to the crystal surface. This is the mode of cleavage characteristic of thin crystals. The single glide along the direction parallel to the surface, and the mechanical twinning obey to the resolved shear stress criterion. The latter is in contrast with the mechanical twinning in bulk crystals where in general the criterion does not hold. The twinning shear demonstrated at the edge of the crystal is much larger than that estimated. High resolution lattice images reveal the consecutive occurrence of twinning and detwinning or simple glide in atomic scale. This is another example exclusively found in thin crystals.