Comparison of Flow and Shear Band Structures in Oriented Columnar Tungsten, Single-Crystal Tungsten-Tantalum, and Intered Tungsten Heavy-Alloy Ballistic Penetrators
The penetration of long rods (L/D10) into standard RHA targets differs with rod failure and flow, which produces erosion and deceleration. Oriented, columnar grained W and  single crystal W-4%Ta rods exhibit dense shear/shear band flow phenomena consisting of overlapping bands ofpredominantly dynamically recrystallised (DRX) grain structures observed by optical metallography and transmission electron microscopy. This flow is contrasted withWHA (93%W, 5%Ni, 2%Fe) sintered rod penetration characterised by penetrator nose failure in blocks which move on narrow shear bands between the blocks and function like microstructural lubricants. From these comparative observations of residual, penetrated rods, strategies to promote rod penetration seem to involve the development of wide, overlapping bands or layers of equiaxed or preferentially oriented, refined microstructures, which facilitate material flow at high strain rates. Microstructural precursors, such as deformation twinning or the enhancement of recrystallisation or related microstructural issues, promoting frequent or overlapping shear bands, either through alloying or processing routes to control the shear instabilities, seem to provide the best strategies to enhance long rod penetration.