A 300µm thick tensile specimen of OFHC copper was subjected to a tensile loading sequence and deformed to a maximal strain of 3.11%. Using the novel three-dimensional X-ray diffraction method of ‘high angular resolution 3DXRD’, the evolution of the microstructure within a deeply embedded grain was characterised in-situ by the behaviour of individual sub-grains. The loading sequence consisted of three continuous deformation stages with strain rates of 1.1 x 10-6 and 3 x 10-2/s, in each case followed by a period of extended stress relaxation at fixed motor positions, as well as an unloading step. In contrast to the deformation stages, during each stress relaxation stage, number, size and orientation of sub-grains were found to be constant, while a minor amount of clean-up of the microstructure was observed as narrowing of the radial X-ray diffraction line profile. The associated decrease in the width of the strain distribution indicated homogenization of the elastic strains present in the deformation structure. During reloading, the sub-grain structure seemingly started to develop further when the entire dislocation structure was deforming plastically. Upon unloading of the sample, the average backward strain of the sub-grains increased.

Stability of Dislocation Structures in Copper Towards Stress Relaxation Investigated by High Angular Resolution 3D X-ray Diffraction. B.Jakobsen, H.F.Poulsen, U.Lienert, J.Bernier, C.Gundlach, W.Pantleon: Physica Status Solidi A, 2009, 206[1], 21-30