The transformation of slip dislocations during twinning of copper-aluminum alloy crystals

Face-centred cubic metals deform by slip until the flow stress and dislocation density are very high, under certain conditions deformation may then proceed by twinning. The geometrical relation between the parent and twinned lattices has been studied in detail (1, 2). In the present work, the dislocation substructures in the parent and twinned portions of the samples were examined in thin foils cut from deformed Cu-8 at. % Al alloy crystals. The data confirm the theoretical predictions, and offer an explanation of some formerly puzzling observations. Consideration of the dislocation transformations indicates that twinning should result in an increase in strength of the material ; this question is also examined.