Dislocations in Deformed Beryllium
High-purity beryllium single crystals were deformed in tension for basal and for prism slip. Some of the work-hardening mechanisms operating at various stages were deduced from observations of dislocations in foils cut from the bulk crystals and from slip lines observed on the surface. Observation of long-edge pairs and edge dipoles in foils cut from crystals deformed in stage I for basal slip suggests that screws have high mobility on the basal plane in stage I and that the crystals exhibit very little hardening. In stage II the presence of numerous edge boundaries was associated with the onset of a rapid rate of work hardening just prior to failure. Three stages of hardening were observed for crystals deformed for prism slip. In stage I the observation of a predominance of screw dislocations suggested that screw dislocation intersections with the grown-in networks had to occur, producing jogs in the screws which acted to impede the motion of the screw dislocations. In stage II complex interactions produced complicated tangled masses of dislocations. In stage III the onset of duplex slip produces stable low-angle boundaries as a result of dislocation interactions along intersections of glide planes.
KeywordsBasal Plane Burger Vector Stack Fault Energy Screw Dislocation Edge Dislocation
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