The study of dipoles in Cu—Al alloys using weak-beam electron microscopy

Abstract

In f.o.c. metals and alloys, dipoles are the predominant dislocation structure during the early stages of plastic deformation. Single crystals of Cu-Al alloys, having low stacking fault energies, have been deformed in tension to the end of stage I of the work-hardening curve. The weak-beam method of electron microscopy has then been used to study the equilibrium configurations of dissociated dipoles having different character and glide-plane separation. By analysing the micrographs, the Burgers vectors of all four partial dislocations can be indexed, the various equilibrium positions identified, and the arrangement of the partial dislocations determined in full. The experimental results are compared with the calculated equilibrium configurations derived by Morton and Forwood (1974, private communication) using linear anisotropic elasticity theory. Various types of equilibrium positions predicted by the theory are observed experimentally and quantitative agreement is good. Deviations from the stress-free configurations are attributed to the influence of friction stress. The results can be used to determine the value of the stacking fault energy in the three Cu-Al alloys, which contain 5, 10 and 15 at. % Al.