Abstract
Cyclic deformation behavior of copper single crystals with a single slip orientation has been investigated intensively. However, geometrical features of dislocation structures in multiple slip orientations have not been satisfactorily explained so far. In this study, therefore, fatigue tests of copper single crystals with [001] and [111] multiple slip orientations were conducted under constant plastic shear strain amplitudes ranging from 1.7 x 10-4 to 1.7 x 10-2 at room temperature. Both high-voltage scanning transmission electron microscopy and electron channeling contrast imaging technique in scanning electron microscopy were used to characterize dislocation structures in fatigued specimens. Characteristic dislocation structures, such as wall, labyrinth and cell, were developed during cyclic deformation and were highly dependent on the stress axis and the applied strain amplitudes. Vein-like structure elongated along the [010] direction was formed at low strain amplitude less than 3 x 10-3. Typical labyrinth structure constituting of the (100) and (001) dislocation walls was evolved in the [001] oriented specimen fatigued at strain amplitude higher than 3 x 10-3. Contrarily, a single set of (111) dislocation walls and cell structure were formed in the [111] oriented specimen. It was concluded that the dislocation wall plane is perpendicular to the direction of the sum of the Burgers vectors for all the dislocations in the active slip systems.
