Dislocation structures produced by low-amplitude fatigue of copper single crystals at 77 K

Abstract

In order to study dislocation structures produced by fatigue at 77 K, copper single crystals were cycled ultrasonically with a frequency of 20 kHz, using an in situ video microscope to view the slip bands and to control the deformation. Because of the sinusoidal stress and strain distribution in the crystals, it was possible to study dislocation structures by TEM, associated with shear stresses as low as 3 MPa up to 46 MPa, the plateau stress at 77 K. The general forms of the loop patches and persistent slip bands were found to be the same as those produced at room temperature. However, the scaling of the structures was different, the channel widths were smaller and more various than those at room temperature, and the density of stacking faulted dipoles was much higher than previously observed. The results are discussed in relation to those observed at room temperature and to the few previous observations reported for 77 K.