Non-spherical voids and lattice reorientation patterning in a shock-loaded Al single crystal

An Al single crystal shock loaded in the <1 2 3> direction and captured at incipient spallation was examined by combining X-ray tomography, electron backscatter diffraction on a scanning electron microscope, and transmission electron microscopy (TEM). Octahedral voids with {1 1 1} faces were a characteristic feature in the spall region. Regular patterns of lattice reorientation were found around individual voids, with lattice rotation being up to 25-30°. Each reorientation pattern consists of a number of reoriented zones. The direction of lattice rotation varies systematically from one zone to another. Four groups of reorientation patterns were identified morphologically in the same metallographic section, which result from different sectioning positions relative to the voids and thus provide equivalently a “serial sectioning” investigation of the deformed volume around the voids. An analysis of the observed reorientation patterns based on active slip systems rationalizes the key features observed and suggests that the systematic reorientation patterns result from the dominance of a single slip system in each individual zone. Microstructures revealed by TEM in the spall region show formation of dislocation cells and extended dislocation boundaries, illustrating the importance of plastic deformation during void growth.

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