Impact resistance of explosively hardened gradient copper

Gradient microstructures offer a promising route to improve dynamic strength, yet their impact mechanisms remain unclear. In this work, oxygen free copper (C10100) cylinders were explosively hardened using a low detonation velocity ammonium nitrate/fuel oil (ANFO) charge, and the charge thickness was tuned to create controllable radial gradients. Optical microscopy (OM) and electron backscatter diffraction (EBSD) quantify millimeter scale refinement in fine grain fraction and near surface grain size reduction from 8.45 to 3.07 μm, together with higher geometrically necessary dislocation density and low-angle grain boundary fraction, and a lower twin-boundary fraction. Radial nanoindentation hardness profiles map the hardness gradient and an area weighted hardness indicator captures the effective contribution of the strengthened shell. Taylor cylinder impact tests at 236 m/s show a monotonic rise in residual length and an estimated dynamic flow stress increase of ∼20% for the strongest condition. Post impact EBSD on recovered specimens indicates that severe loading drives both untreated and hardened states toward similarly saturated substructures, implying that preexisting gradients mainly regulate early stress and strain partitioning. Molecular dynamics modeling of Taylor impact isolates grain size gradients, twins, and preexisting dislocations, and uses waveform characteristics (peak compressive magnitude, wavefront width, blunting index) and defect-localization entropy to link microstructure to stress-wave evolution. Grain gradients broaden the compressive front, twins promote more spatially distributed planar defects and can suppress gradient driven broadening, while dislocations sharpen and amplify peaks with strong blunting reduction. These results establish microstructure informed guidelines for impact resistant metallic materials.