Work Hardening and Dislocation Arrangement of fcc Single Crystals. II. Electron Microscope Transmission Studies of Ni–Co Single Crystals and Relation to Work-Hardening Theory

Abstract

The dislocation arrangement in the primary glide plane of deformed Ni–Co crystals of different compositions and stacking fault energies was investigated by the transmission electron microscope technique. The thin foils were found to contain mainly dislocations of the primary glide system close to the edge orientation. Very few screw dislocations were observed; they were presumably lost during the preparation. Straight dislocations in 〈110〉 directions, presumably Lomer-Cottrell dislocations, were found in particular at intermediate and low stacking fault energies. The dislocation density shows local variations so that ``dislocation braids'' can be discerned from the background. For Ni+40% Co, the dislocation densities and arrangements are compared with slip line results obtained from the same crystals. These results are found to be compatible with the so-called glide-zone model and the geometrical interpretation of the slip-line pattern based on it. The final section deals with the dynamic aspect of plastic deformation and with the theory of work hardening by long-range stresses. It is shown that the experimental observations fit this theory. Some objections that have been raised against the theory are discussed and met.