Characterizing Inhomogeneous Deformation Substructure in Large Single Crystals by Microscopy and XRD - A Synergystic Analysis

Extract

Characterization of deformed crystals containing extensive inhomogeneities and localized lattice reorientations presents a formidable challenge, particularly when the available sample volume is limited and/or irregular in configuration. The crystals analyzed in this work were originally high-symmetry single crystal tungsten rods, 6.9 mm in diameter and 102 mm long, which had been ballistically launched against steel blocks. At ordnance velocities (1.5 km/sec), the rods evert as they penetrate the block, resulting in a cylindrical cavity partially lined with a hollow tube of tungsten, with a slug resting at the bottom. These tungsten residuals contained many localizations, fractures, and assemblages of discrete sub-entities, typically 100-200 microns in size, within a macroscopic flow pattern extending over many millimeters. The measured cavity depths displayed a strong crystallographic symmetry dependence. Because the post-event samples, which were either blocks containing polished axial sections through the cavity or loose ejecta, were both massive and frangible, area-resolved X-ray diffraction, utilizing a fine-beam Laue technique with a precision specimen translator to permit correlation with micrographs, was used to map and characterize the lattice sub-structure.