SummaryThe influence of degree of dissociation on the diffraction contrast from a Frank dislocation for lll, 220, and 020 reflections has been investigated using the technique devised by Head and Humble for computing electron microscope images.The diffraction contrast from a dissociated Frank dislocation differs in several ways from that of an undissociated dislocation. For 111 reflections, strong contrast occurs when g. u oF O. For 220 reflections, images are single and continuous with strong contrast on one side only. The strong contrast does not invert from side to side for +g and -g. For 020 reflections the extent to which reversal of contrast occurs in ± g is a function of g, the beam direction, and the separation of the Shockley and stair-rod dislocations.The computations for an undissociated Frank dislocation are in general agreement with previous computations, but indicate that a Frank dislocation may show strong contrast for certain beam directions when g. b = ±l.

SummaryThe Burgers vectors of the dislocations bounding steps in the stacking fault in Frank dislocation loops in quenched silver and copper-aluminium alloys have been identified by comparison of experimental electron microscope images and images computed using the Head-Humble technique. The steps in the fault are generally acute, faulted, and bordered by t

SummaryExperimental and computed images for edges of Frank dislocation loops in quenched copper-aluminium alloys and in quenched silver are compared. The comparison shows that Frank dislocations are dissociated in these materials. By matching the computed and experimental images, the degree of dissociation is determined and the stacking fault energy of the various materials is estimated.