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 arrang ements in persistent slip bands (PSBs) and the bundle structure in the matrix. Long-range internal stresses are expected to arise in the PSB s. The change of these stresses within the deformation cycle is invest igated 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 resolve d changing their sign within each half-cycle. The saturation of the in ternal stresses within each half-cycle indicates macroyielding which m ay be interpreted as plastic yielding of the PSB walls at a local yiel d stress of about 120 MPa. (C) 1997 Elsevier Science B.V.