Dynamic deformation and adiabatic shear microstructures associated with ballistic plug formation and fracture in Ti–6Al–4V targets

Cylindrical, flat-nose, 4340 steel projectiles (2.0 cm height) were impacted onto Ti–6Al–4V targets (2.5 thick) at velocities ranging from 633 to 1027 m/s. Plug formation was observable at 633 m/s and exited the target between 1006 and 1027 m/s. Adiabatic shear bands (ASBs) composed of dynamically recrystallized (DRX) grains and cracks formed both vertically and horizontally (parallel or perpendicular) to the impact axis. The ASB characteristically white-band thickness varied from 5 to 40 μm, with the thicker bands occurring at the highest impact velocity. ASBs and cracks increased in frequency with increasing impact velocity, forming a cylindrical flow regime characterizing the plug. TEM analysis showed a greater than order of magnitude decrease in the DRX regime composing the ASBs, while EBSD analysis showed a residual DRX, grain-size regime varying from 50 to 900 nm. There was no evidence for an α → β transformation occurring within the ASB/DRX regime.