The dislocation structures which were introduced by the cyclic deformation of [017] critical and [¯112], [¯117] conjugate double-slip oriented single crystals were investigated by using transmission electron microscopy and the electron channeling contrast technique of scanning electron microscopy. It was found that the crystallographic orientation had a marked effect upon the dislocation structures in cyclically saturated critical and/or conjugate double-slip oriented single crystals. It was suggested that such an orientation dependence of the dislocation structure could account well for the corresponding orientation dependence of the plateau behavior in the cyclic stress-strain curve. In the case of cyclic deformation of the [¯112] crystal, the formation of persistent slip band ladder structures was a general phenomenon. Persistent slip bands occurred even at low strain amplitudes which were below the plateau region in the cyclic stress-strain curve. The experimental results indicated that there was no complete one-to-one correlation between the formation of persistent slip bands and the presence of a plateau region in the cyclic stress-strain curve. In certain double-slip oriented single crystals, the actual size of the microstructures was found to change with varying strain amplitude. This was one of the main reasons for the disappearance of a clear plateau in the cyclic stress-strain curve. A decrease in the width of vein channels with increasing strain amplitude, and the absence of a persistent slip band ladder structure, were the main reasons for the non-existence of a clear plateau region in the cyclic stress-strain curve of the [¯117] crystal. The joint effects of a change in scale of the labyrinth structure, and the formation of persistent slip band ladder-like structures, led to the occurrence of only a narrow quasi-plateau in the cyclic stress-strain curve of the [017] crystal.

Dislocation Structures in Fatigued Critical and Conjugate Double-Slip Oriented Copper Single Crystals. X.W.Li, Y.Umakoshi, B.Gong, S.X.Li, Z.G.Wang: Materials Science and Engineering A, 2002, 333[1-2], 51-59