X-ray diffraction analysis of internal stresses in the dislocation structure of cyclically deformed nickel single crystals

Typical dislocation configurations appearing after cyclic deformation of nickel crystals oriented for single slip are the ladder-like arrangements in persistent slip bands (PSBs) and the bundle structure in the matrix. Long-range internal stresses are expected to arise in the PSBs. The change of these stresses within the deformation cycle is investigated by an analysis of asymmetric X-ray line profiles. For crystals with a pure matrix structure or with a low volume fraction of PSBs, no significant long-range stresses occur. In dislocation structures with a PSB volume fraction above 20%, long-range stresses could be resolved changing their sign within each half-cycle. The saturation of the internal stresses within each half-cycle indicates macroyielding which may be interpreted as plastic yielding of the PSB walls at a local yield stress of about 120 MPa.