DIRECT OBSERVATIONS AND COMPARISON OF CRATER CROSS-SECTION MICROSTRUCTURES IN COPPER TARGETS FOR ALUMINUM PROJECTILES IMPACTING AT 1.4 AND 6.7 KM(-1)

Light and transmission electron microscopy observations of impact crat er-related microstructures in copper targets have revealed dramatic di fferences in the extent and type of microstructures. For a crater form ed by a 6.4 mm diameter aluminium (1100) spherical projectile impactin g at 1.4 km s(-1), a narrow (similar to 20 mu m) recrystallized zone e xtended axially outward from the crater wall, with dislocation cells w hich increased in size extending from this zone. By comparison, a crat er formed by a 3.2 mm diameter aluminium (1100) spherical projectile i mpacting at 6.7 km s(-1) exhibited a recrystallization zone extending more than 200 mu m axially from the crater wall, a connecting zone of increasingly dense microbands, having an axial width of about 2000 mu m. This zone converged upon a region of dislocation cells which increa sed in size away from the crater wall. These observations highlight im portant microstructural differences in cratered metal targets in the h ypervelocity impact regime in contrast to the lower-velocity regimes w here shock-wave and related ultra-high-strain-rate effects are unimpor tant.