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 size containing similar to 10(10) dislocations/cm(2) (Vickers hardness of 0.89 GPa); an annealed, 124 mu m grain size containing 10(9) dislocations/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) were impacted with 3.18 mm diameter ferritic stainless steel projectiles at nominal velocities of 0.7, 2 and 5 km s(-1). Like companion experiments utilizing soda-lime glass projectiles (Part I), absolute grain size of the target was observed to be less important than the dislocation density in the cratering process. At low im pact velocity, depth/diameter ratios were observed to increase dramatically in contrast to less dense soda-lime glass impactors, and the impactor behaviours were also very different. The ferritic stainless steel impactors spalled into small fragments at or above 2 km s(-1) impact velocity and a significant fraction of these fragments remained in the craters. No significant melt phenomena were observed either in connection with projectile fragmentation or in the crater-related, residual microstructures. Dynamic recrystallization, dislocation cell structures and microbands were significant microstructural features in the targets. They extended from the crater walls and contributed to hard ness profiles within the cratered targets. These hardness profiles and actual hardness zones generally increased in extent from the crater wall with both impact velocity and projectile density.