THE NATURE AND FORMATION OF BANDS OF DEFORMATION IN SINGLE CRYSTALS OF α-PHASE COPPER–ALUMINIUM ALLOYS

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Abstract
The mechanism of the deformation in tension of [321] axis square-sectioned single crystals of α-phase copper–aluminium alloys with and surfaces has been studied. Extensive use has been made of interference microscopy and carbon replicas for the determination of the surface topography of the bands of deformation. It has been shown that, in addition to the discrete slip lines which are seen with the optical microscope and in replicas, there is a background of plastic deformation on a much finer scale which is not resolved. The integrated step height across bands of deformation corresponding with this fine slip can be measured on the interferograms. The integrated step height between corresponding points on the opposite surfaces was found to be equal. The studies of surface topography were supplemented by work on the nature of the distributions of dislocations within the crystals by etching and transmission electron microscopy. It was found that the dislocations are largely present as interleaved pileups of parallel positive and parallel negative dislocations in near-edge orientations and as closely spaced multipolar distributions. Large pileups of several hundred dislocations have been observed and correlated with surface slip lines. They appear to be introduced as avalanches from surface sources. Characteristic features of this previously unrecognized type of band of deformation have been established and the mechanism proposed for the formation of the bands recalls many of the features of the dynamical model for the multiplication of dislocations discussed by Frank in 1947. The background on which the slip lines are superimposed appears to be due to the limited activation by the shear stress within the band of deformation of a uniform distribution of sources.