In situ X-ray diffraction peak profile analysis during plastic deformation in [001]-oriented Cu single crystals was carried out using synchrotron radiation. Characteristic changes of the hardening coefficient indicate that a transition occurred from stage-III to stage-IV which was observed for the first time in a single crystal under low temperature deformation conditions. The long-range internal stresses, the dislocation arrangement parameters and the fluctuations of the dislocation density show non-monotonous changes at this transition suggesting that the dislocation structure, especially within the cell-wall regions, revealed a second-order phase transition. A microscopic dislocation model was introduced which not only illustrates the break of symmetry, but also describes well the development of new grains (“fragmentation”) during plastic deformation.

A Second-Order Phase-Transformation of the Dislocation Structure during Plastic Deformation Determined by in situ Synchrotron X-Ray Diffraction. E.Schafler, K.Simon, S.Bernstorff, P.Hanák, G.Tichy, T.Ungár, M.J.Zehetbauer: Acta Materialia, 2005, 53[2], 315-322