Effect of shock compression method on the defect substructure in monocrystalline copper

Monocrystalline copper samples with orientations of [0 0 1] and [2 2 1] were shocked at pressures ranging from 20 to 60 GPa using two techniques: direct drive lasers and explosively driven flyer plates. The pulse duration for these techniques differed substantially: 40 ns for the laser experiments at 0.5 mm into the sample and 1.1∼1.4 μs for the flyer-plate experiments at 5 mm into the sample. The residual microstructures were dependent on orientation, pressure, and shocking method. The much shorter pulse duration in the laser driven shock yielded microstructures in recovery samples closer to those generated at the shock front. For the flyer-plate experiments, the longer pulse duration allows shock-generated defects to reorganize into lower energy configurations. Calculations show that the post-shock cooling for the laser driven shock is 103 ∼ 104 faster than that for plate-impact shock, increasing the amount of annealing and recrystallization in recovery samples for the latter. At the higher pressure level, extensive recrystallization was observed in the plate-impact samples, while it was absent in laser driven shock. An effect that is proposed to contribute significantly to the formation of recrystallized regions is the existence of micro-shear-bands, which increase the local temperature beyond the prediction from adiabatic compression.