INFLUENCE OF HETEROGENEOUS DISLOCATION ARRANGEMENTS ON X-RAY-DIFFRACTION PROFILES MEASURED ON CYCLICALLY DEFORMED NICKEL SINGLE-CRYSTALS .1. PROFILE BROADENING AT DIFFERENT PLASTIC STRAIN AMPLITUDES

X-ray diffraction profiles of Bragg reflections were measured on cycli cally deformed nickel single crystals of different orientations with a high-resolution double crystal diffractometer. The mesoscopic disloca tion structures beneath the crystal surfaces were studied by scanning electron microscopy using the channelling contrast of backscattered el ectrons. Changes of internal stresses on different length scales can b e inferred from the characteristic dependence of the diffraction profi le broadening on the plastic strain amplitude. Short-range stresses ar e predominant in the matrix structure of crystals cyclically deformed at small strain amplitudes. At higher amplitudes, in the plateau regio n of the cyclic stress-strain curve, remarkable long-range stresses ar ise in crystals of all orientations due to the existence of ladder-lik e, cellular and other dislocation structures.