Abstract
Discontinuous slip at the initial stage of easy glide in copper rich Cu–Al alloy crystals is studied in detail by means of observations of slip lines and etch pits. A new type of discontinuous slip is observed in thin crystals of alloys containing aluminium lower than 3 at% below 200 K . It takes place by a similar process to the propagation of Lüders band. But the boundary between the deformed and the undeformed region is normal to the slip direction and moves discontinuously resulting in abrupt drop in the stress. Dislocations in the deformed region are able to move under a lower stress than the yield stress, so that it is an important evidence that the frictional stress due to solute atoms does not determine the yield stress. This mode of deformation is able to accelerate the operation of the primary slip system without activating the secondary slip systems. The extensive easy glide region observed in low concentration fcc alloy crystals is related to this mode of deformation.
