X-ray Microdiffraction Characterization of Deformation Heterogeneities in BCC Crystals
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X-ray Microdiffraction Characterization of Deformation Heterogeneities in BCC Crystals K.R. Magid1, E.T. Lilleodden2, N. Tamura3, J.N. Florando4, D.H. Lassila4, M.M. LeBlanc4, R.I. Barabash5 and J.W. Morris, Jr.1 1
Department of Materials Science and Engineering, University of California-Berkeley, Berkeley, CA 94720, USA 2 Institut für Materialforschung II, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany. 3 Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA 4 Engineering Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 5 Oak Ridge National Laboratory, Oak Ridge, TN, USA ABSTRACT The deformation behavior of BCC metals is being investigated by x-ray microdiffraction measurements (µXRD) for the purpose of characterizing the dislocation structure that results from uniaxial compression experiments. The high brilliance synchrotron source at the Advanced Light Source (Lawrence Berkeley National Lab) and the micron resolution of the focusing optics allow for the mapping of Laue diffraction patterns across a sample. These measurements are then analyzed in order to map the distribution of residual stresses in the crystal. An important finding is the observation of Laue spot "streaking", which indicates localized rotations in the lattice. These may represent an accumulation of same-sign dislocations. Theoretical modeling of the diffraction response for various slip systems is presented, and compared to experimental data. Preliminary results include orientation maps from a highly strained Ta bicrystal and a less highly strained Mo single crystal. The orientation maps of the bicrystal indicate a cell-like structure of dense dislocation walls. This deformation structure is consistent with previous OIM studies of the same crystal. The results suggest that µXRD may be a particularly useful tool for microscale studies of deformation patterns in a multi-scale investigation of the mechanisms of deformation that ranges from macroscopic deformation tests to high resolution TEM studies of dislocation structures. INTRODUCTION The deformation of body-centered cubic (BCC) crystals is an important subject of current research, both for its inherent scientific interest [1] and because it is the focus of an extensive, on-going effort in the computer simulation of dislocation plasticity [2]. The modeling effort, in particular, has created a need for complementary experimental research to identify wellcharacterized examples that can be used as reliable test cases. The construction of well-characterized examples of bulk deformation poses a number of experimental challenges whose solution would seem to require a “multi-scale” approach to the problem. The engineering result of plasticity is macroscopic deformation, which is tested by deforming bulk samples in large machines. The detailed mechanisms of plastic deformation ordinarily involve dislocation motion on the micro- to nanoscale, and are best studied with transmission electron microscopy. Given the usual heterogeneity of p
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