Cross-sectional TEM studies of plastic wave attenuation in shock loaded NiAl

The role of plasticity and overall shear strength of metals subjected to weak and moderate shock waves is not well understood. The plastic response of shocked metals is known to vary with applied pressure although these variations are different for each material. Weakly shocked single crystals will tend to display plastic anisotropy and anisotropic Hugoniots at least up to the overdrive pressure. In the current study, cross-section transmission electron microscopy (XTEM) has been used to elucidate these effects in single crystals of nickel aluminide (NiAl). Single crystals of NiAl (5 mm diameter) were cut and polished down to 100–300 μm along three loading directions 〈0 0 1〉, 〈1 1 0〉, 〈1 1 1〉. Each of the three samples was subjected to laser induced shocks of around 15 GPa. Cross-sectional transmission electron microscopy (XTEM) samples were extracted from shocked samples and were used to observe dislocation structures and lattice rotations with selected area diffraction patterns. Regions within 2 μm of the drive surface exhibited lattice rotation gradients up to about 1400°/mm in 〈1 1 0〉 samples. Following the first few microns, the lattice rotations were found to decay rapidly over the next 5 μm. These trends were also seen in orientation imaging microscopy (OIM) data. The lattice rotation gradients correlated well with pressure decay from 1D hydrodynamic calculations.