In situ TEM observations of the cyclic dislocation behaviour in persistent slip bands of copper single crystals

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Abstract
The dislocation processes occurring during cyclic deformation in persistent slip bands (PSBs) have been investigated in copper single crystals by in situ electron microscopy. The shapes of screw dislocations and of dislocation loops expanding in the channels of PSBs of different widths have been examined under stress. The local stress values and the shape of the stress profiles across PSBs have been determined, allowing for a comparison between experimental and computed dislocation shapes in such non-uniform stress fields. Several microstructural parameters involved in the model elaborated by Mughrabi and Essmann for the saturation stage of cyclic deformation are discussed quantitatively. The present results confirm the basic mechanisms proposed by these authors. In addition, it is found that because of many interactions with obstacles, the screw dislocations move as individuals rather than in groups, and the relative contribution of edge dislocations to the deformation of PSBs cannot be neglected. The influence of the channel width on the critical stress for dislocation motion appears to follow a Frank-Read-type relation, and some consequence of this upon the general mechanisms of PSB operation during cyclic saturation are discussed.