In-situ cyclic deformation of Al single crystals in the HVEM and the concept of internal backstresses

Aluminum single crystals were cyclically deformed in single-slip at small strain amplitudes at 77 K to presaturation. In-situ cyclic deformation experiments were successfully performed on thin foils extracted from these (predeformed) by the X-Y technique, where thin foils are stressed in alternating perpendicular directions. Screw dislocations span the channel and easily move and reverse direction with shear reversal. Our experiments indicate that loops frequently expand from the dipole bundles into the channel and the edge component is absorbed by nearby bundles leaving screw segments behind. There is no obvious evidence for internal backstresses that assist plastic deformation on reversal of the applied shear.