EFFECT OF INITIAL MICROSTRUCTURE ON HIGH-VELOCITY AND HYPERVELOCITY IMPACT CRATERING AND CRATER-RELATED MICROSTRUCTURES IN THICK COPPER TARGETS .2. STAINLESS-STEEL PROJECTILES

Three different, thick copper targets (an as-received, 98 mu m grain s ize containing similar to 10(10) dislocations/cm(2) (Vickers hardness of 0.89 GPa); an annealed, 124 mu m grain size containing 10(9) disloc ations/cm(2) (Vicker's hardness of 0.69 GPa; and a 763 mu m grain size containing 10(9) dislocations/cm(2) (Vickers hardness of 0.67 GPa) we re impacted with 3.18 mm diameter ferritic stainless steel projectiles at nominal velocities of 0.7, 2 and 5 km s(-1). Like companion experi ments utilizing soda-lime glass projectiles (Part I), absolute grain s ize of the target was observed to be less important than the dislocati on density in the cratering process. At low im pact velocity, depth/di ameter ratios were observed to increase dramatically in contrast to le ss dense soda-lime glass impactors, and the impactor behaviours were a lso very different. The ferritic stainless steel impactors spalled int o small fragments at or above 2 km s(-1) impact velocity and a signifi cant fraction of these fragments remained in the craters. No significa nt melt phenomena were observed either in connection with projectile f ragmentation or in the crater-related, residual microstructures. Dynam ic recrystallization, dislocation cell structures and microbands were significant microstructural features in the targets. They extended fro m the crater walls and contributed to hard ness profiles within the cr atered targets. These hardness profiles and actual hardness zones gene rally increased in extent from the crater wall with both impact veloci ty and projectile density.