| The microstructures of long rod [001] single-crystal W-5% Ta penetrators grown by zone-melt processing (ZM), and W penetrators grown by both chemical vapor deposition (CVD) and ZM processing were compared and examined before and after penetration into rolled homogeneous armor (RHA) steel targets. The initial Vickers microhardness average value for the CVD-W rods was 417 Vickers hardness number. (VHN) in contrast to 485 VHN for the ZM W and W-5% Ta rods as a consequence of an order of magnitude larger dislocation density. Examination of in-target residual cross-section rod heads and rod erosion fragments was performed utilizing scanning and transmission electron microscopy (SEM and TEM) as well as optical metallography. Consistent with prior, related studies, rod penetration (at 1.2 to 1.4 km/s) was facilitated by super plastic deformation (SPD)-induced solid-state flow, cleavage cracking, shear instabilities, and overlapping adiabatic shear bands characterized by dynamic re-crystallization (DRX).; Peripherally along both sides of the penetrator head (high strain points), the DRX zone is followed by an adiabatic shear band or many nucleating bands which allow flow and erosion to occur between this surface zone and the rod head center. These high strain points create a flow characteristic which seems to indicate a vortex-like effect creating a hot zone characterized by large, equiaxed grains. (Abstract shortened by UMI.)... |
