INFLUENCE OF HETEROGENEOUS DISLOCATION ARRANGEMENTS ON X-RAY-DIFFRACTION PROFILES MEASURED ON CYCLICALLY DEFORMED NICKEL SINGLE-CRYSTALS - PART-II - SHAPE CHANGES OF DIFFRACTION PROFILES DURING A DEFORMATION CYCLE

Nickel single crystals of different orientations were deformed cyclica lly into the stage of mechanical saturation and investigated by high r esolution X-ray diffraction after unloading from different points of t he mechanical hysteresis loop. Characteristic changes of the diffracti on profile shape were found indicating a variation of long-range inter nal stresses within the hysteresis cycle. By an analysis of the diffra ction profiles these stresses could be determined for different disloc ation structures. For example, the internal stresses arising in persis tent slip bands (PSBs) were estimated. From the experimental results t he conclusion is drawn that macroyielding occurs not only in PSBs but also in regions with a dislocation structure typical for the [001] sam ple orientation, provided the strain amplitude exceeds a threshold val ue.