DescriptionFor deformed materials, an asymmetry of x-ray line profiles is attributed by the classical composite model to a weighted superposition of contributions from two different constituents of a dislocation cell structure: dislocation walls and dislocation-depleted cell interiors strained elastically in opposite direction. By high resolution reciprocal space mapping, new insight in the contribution of the dislocation-poor regions is gained and simultaneously earlier criticism concerning the dislocation content relieved. With high angular resolution 3D X-ray Diffraction established at the Advance Photon Source, reciprocal space mapping of selected reflections of individual grains in the bulk of a specimen is performed in-situ during tensile loading. For deformed grains with dislocation cell structures, the intensity distribution in reciprocal space consists of bright sharp peaks superposed on a cloud of enhanced intensity. The high-intensity peaks are identified as diffraction signal from (almost) dislocation-free subgrains, whereas the cloud of lower intensity originates from the dislocation walls of the dislocation structure. Both, the azimuthal and radial positions of individual high-intensity peaks differ from each other indicating not only small orientation differences, but also a significant variation of their elastic strain state. The dislocation-free subgrains experience quite different elastic strains - in average opposing the elastic strains caused by the tensile load. Based on this finding modification of the classical composite model is suggested in the sense that the dislocation-poor regions do not contribute collectively with a common profile broadened by the dislocation density in these regions, but rather each individual dislocation-free subgrain contributes with an own sharp profile at a slightly different backward strain.
|6 Aug 2012 → 10 Aug 2012
|61st Annual Conference on Applications of X-ray Analysis
|Denver, CO, United States