Mechanical Hysteresis and Dislocation-Dislocation Interactions in Copper Crystals

Half-cycle mechanical hysteresis loops, at positive stress bias, representing damping frequencies in the range of ≈10−1 Hz were performed on copper crystals at room temperature. The hysteretic character and stability of the dislocation structure were explored by repetitive stress cycling at constant stress amplitude. It was found that the decrement decreased with continued stress cycling and eventually reached a saturation value. Changes in the decrement, with cycling, provided an extremely sensitive way of detecting dislocation rearrangements at low stress levels. Sectioning and etch pitting of the crystals was performed in order to reveal quantitatively both the forest and primary dislocation structures associated with the hysteresis behavior. Correlation of the damping and etch-pit data indicated that low-frequency mechanical hysteresis could be attributed to ``pinning'' of primary dislocations at forest dislocation junctions.