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Abstract
In face-centred-cubic metals the {111} planes are the predominant slip planes. Glide on other less densely packed planes has hitherto not been encountered in specimens deformed at room temperature. Glide dislocations can react with each other and form Lomer-Cottrell (LC) locks; they are split on two intersecting {111} planes and therefore sessile. If they were not split they would be able to glide on {001} planes.
Oriented single crystals of Ni, Cu and Ag have been deformed in tension into stage II and the dislocation structure of {001} foils investigated by transmission electron microscopy. The Burgers vectors and glide planes were identified unambiguously. Composite dislocations (b = a/2(110)), which can glide on {001} planes and originate in a transformation of LC dislocations, were found to occur frequently; they can leave the {001} plane and cross-slip onto a {111} plane. These phenomena were observed in all three metals in spite of their different values of the stacking fault energy. To explain glide on {001} planes a new model, deduced from careful analysis of the dislocation configurations, has been worked out. The mechanism is based on the mobility of the constricted node and does not require large stresses. Thus good agreement with the experimentally observed results is obtained.
