Analysis of the existence of long range internal stresses in deformed metals

UnrestrictedThis thesis examines the existence of long range internal stresses (LRIS) in deformed metal single crystals. Asymmetry in strain broadened x-ray diffraction (XRD) line profiles is often given as evidence of the existence of LRIS. It is found that experimental evidence in the literature is unable to definitively separate whether measured asymmetry is due to LRIS or due to diffraction effects independent of LRIS. Single crystals of copper were monotonically deformed in order to produce representative samples with asymmetry. Synchrotron experiments were performed using differential aperture x-ray microscopy (DAXM) to make spatially resolved measurements of elastic strains within individual dislocation cells for the very first time. Broad distributions of elastic strains were found, and the relative strains between cell walls and cell interiors are in agreement with the existence of LRIS. Simulations of XRD found asymmetry due to dislocation dipoles and due to stacking faults. The configuration of defects is found to be important. These simulation results, using realistic dislocation densities, suggest that asymmetry in real materials is possible in cases where LRIS is absent