Cyclic deformation of [001] aluminium single crystals

Cyclic deformation in symmetric push-pull of pure aluminium single crystals with [001] orientation has been carried out at constant plastic strain amplitudes within the range 10−4–10−3. The cyclic stress response curves are characterised by rapid hardening, softening and secondary hardening without saturation of the stress at any strain level. Fatigue failure by traditional crack growth was never observed, but the specimens failed by a complicated plastic collapse mechanism. Traditional slip lines were seldom observed. Instead, very characteristic deformation patterns with a cord-like appearance at low strain amplitudes, and a tweed-like appearance at higher strain amplitudes developed. In the collapse state, slip lines clustered in macrobands were also formed. The dislocation structure was studied by TEM and found to consist of {100} dislocation walls and elongated cells. In addition, spherical subcells were observed on the dislocation walls.