The low-stress and high-temperature creep in LiF single crystals: An explanation for the So-called Harper-Dorn creep
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Singh, Shobhit Pratap↗
Engineering topics
Kassner, Michael E.
Publications and source records attributed to Kassner, Michael E..
Basis for the Bauschinger effect in copper single crystals: changes in the long-range internal stress with reverse deformation
In this study, the long-range internal stresses (LRIS) associated with the Bauschinger effect were investigated using synchrotron X-ray microbeam diffraction and reversed deformation experiments. [100]-oriented Cu single crystals were deformed in compression to approximately -0.3 true strain, followed by tension to a strain of approximately +0.02. Two conclusions are arrived at from this work: First, the LRIS are confirmed in this work to be small relative to the applied stress both before and after reversal. Second, the LRIS persist after 2% reversed strain despite a significant drop in the overall dislocation density by dynamic recovery. This appears to satisfy the necessary condition for LRIS to significantly contribute to a Bauschinger effect in materials. Lastly, the pronounced Bauschinger effect in Cu is probably best rationalized by a combination of both the LRIS and the Orowan–Sleeswyk model that relies on a non-uniform distribution of dislocation obstacles without a substantial LRIS.
36 MATERIALS SCIENCE↗
Synchrotron X-ray microbeam diffraction measurements of full elastic long range internal strain and stress tensors in commercial-purity aluminum processed by multiple passes of equal-channel angular pressing
Synchrotron X-ray microbeam diffraction was used to measure the full elastic long range internal strain and stress tensors of low dislocation density regions within the submicrometer grain/subgrain structure of equal-channel angular pressed (ECAP) aluminum alloy AA1050 after 1, 2, and 8 passes using route B C . This is the first time that full tensors were measured in plastically deformed metals at this length scale. The maximum (most tensile or least compressive) principal elastic strain directions for the unloaded 1 pass sample for the grain/subgrain interiors align well with the pressing direction, and are more random for the 2 and 8 pass samples. The measurements reported here indicate that the local stresses and strains become increasingly isotropic (homogenized) with increasing ECAP passes using route BC. The average maximum (in magnitude) LRISs are -0.43 σ a for 1 pass, -0.44 σ a for 2 pass, and 0.14 σ a for the 8 pass sample. Furthermore, these LRISs are larger than those reported previously because those earlier measurements were unable to measure the full stress tensor. Significantly, the measured stresses are inconsistent with the two-component composite model.
36 MATERIALS SCIENCE↗
Validating classical line profile analyses using microbeam diffraction from individual dislocation cell walls and cell interiors
Dislocation structures in deformed metals produce broad asymmetric diffraction line profiles. During analysis, these profiles are generally separated into two nearly symmetric subprofiles corresponding to diffraction by dislocation cell walls and cell interiors. These subprofiles are then interpreted using complex models of dislocation-based line broadening. Until now, it has not been possible to test the many assumptions that are made in such an analysis. Here, depth-resolved microbeam diffraction was used to measure diffraction line profiles from numerous individual dislocation cell walls and cell interiors in a heavily deformed Cu single crystal. Summing these profiles directly constructed the cell-interior and cell-wall subprofiles that have been approximated in the line profile analysis literature for the past 30 years. Direct comparison between the reconstructed subprofiles and the macroscopic asymmetric line profile from the same sample allows the first direct tests of many of the assumptions that have been used for interpreting these X-ray measurements.
36 MATERIALS SCIENCE↗