Influence of Heterogeneous Dislocation Arrangements on X-ray Diffraction Profiles Measured on Cyclically Deformed Nickel Single Crystals

Nickel single crystals of different orientations were deformed cyclically into the stage of mechanical saturation and investigated by high resolution X-ray diffraction after unloading from different points of the mechanical hysteresis loop. Characteristic changes of the diffraction profile shape were found indicating a variation of long-range internal stresses within the hysteresis cycle. By an analysis of the diffraction profiles these stresses could be determined for different dislocation structures. For example, the internal stresses arising in persistent slip bands (PSBs) were estimated. From the experimental results the conclusion is drawn that macroyielding occurs not only in PSBs but also in regions with a dislocation structure typical for the [ ] sample orientation, provided the strain amplitude exceeds a threshold value.