Analysis of the stacking faults of dissociated glide dislocations in F.C.C. metals

In f.c.c. crystals the dislocations gliding on {111} planes are split into partial dislocations bounding a stacking fault ribbon. In principle the nature of these faults could be either intrinsic or extrinsic. The weak-beam method of electron microscopy is used in combination with bright-field images to study both, the partials and the stacking faults. The different contrast intensities of the partials observed in the weak-beam images are a good means to determine the sign of their Burgers vector. Several hundred dissociated glide dislocations are studied in deformed single crystals of pure Ag and CuAl alloys. All the analysed faults are intrinsic and not a single exception is encountered. This result can be interpreted by differences in the nucleation mechanism of faults formed by shear.