EFFECT OF INITIAL MICROSTRUCTURE ON HIGH-VELOCITY AND HYPERVELOCITY IMPACT CRATERING AND CRATER-RELATED MICROSTRUCTURES IN THICK COPPER TARGETS .1. SODA-LIME GLASS PROJECTILES

Three uniquely different initial microstructure regimes were created i n 2.5 cm thick copper targets: an as-received 98 mu m grain size conta ining similar to 10(10) disiocations/cm(2). (Vickers hardness of 0.89 GPa); an annealed 124 mu m grain size containing similar to 10(9) disl ocations/cm(2) (Vickers hardness of 0.69 GPa); and a 763 mu m grain si ze containing similar to 10(9) dislocations/cm(2) (Vickers hardness of 0.67 GPa). Each of these target plates was impacted by 3.18 mm diamet er soda-lime glass spheres at nominal impact velocities of 2, 4 and 6 km s(-1). Grain size was observed to have only a very small or negligi ble contribution to cratering, while the dislocation density had a con trolling influence on both the target hardness and the cratering proce ss. Residual crater hardness profiles were correlated with specific mi crostructure zones extending from the crater wall into the target, and both hardness profiles a nd residual microstructures differed for eac h specific target, and for each different impact velocity. Microbands coincident with traces of {111} planes were associated with a zone of residual target hardening and increased with increasing grain size and impact velocity. No significant melt-related phenomena were observed, and crater-related target flow occurs by solid-state plastic flow thr ough dynamic recrystallization, forming a narrow, softened zone at the crater wall.