Slip competition and rotation suppression in tantalum and copper during dynamic uniaxial compression

Abstract

When compressed, a metallic specimen will generally experience changes to its crystallographic texture due to plasticity-induced rotation. Ultrafast x-ray diffraction techniques make it possible to measure rotation of this kind in targets dynamically compressed over nanosecond timescales to the kind of pressures ordinarily encountered in planetary interiors. The axis and the extent of the local rotation can provide hints as to the combination of plasticity mechanisms activated by the rapid uniaxial compression, thus providing valuable information about the underlying dislocation kinetics operative during extreme loading conditions. We present large-scale molecular dynamics simulations of shock-induced lattice rotation in three model crystals whose behavior has previously been characterized in dynamic-compression experiments: tantalum shocked along its [101] direction, and copper shocked along either [001] or [111]. We find that, in all three cases, the texture changes predicted by the simulations are consistent with those measured experimentally using in situ x-ray diffraction. We show that while tantalum loaded along [101] and copper loaded along [001] both show pronounced rotation due to asymmetric multiple slip, the orientation of copper shocked along [111] is predicted to be stabilized by opposing rotations arising from competing, symmetrically equivalent slip systems.

Femtosecond Diffraction and Dynamic High Pressure Science

“…In previous laser-plasma shock experiments that viewed rotation in single crystals 175 the Taylor model was used 166 , where line elements perpendicular to the compression access are conserved. However, it can easily be shown that the situation is more complex for single slip when the deformation of the crystal takes place under the boundary conditions of uniaxial compression, and Heighway and Wark have shown that neither of these classic models correctly predicts the degree of rotation for a single crystal subject to uniaxial compression and undergoing single slip 176 ; furthermore, there is good evidence from MD simulations that multiple slip systems are active in these experiments 177 . Of course, in real polycrystalline materials, such as those observed in the Wehrenberg experiments, whilst the condition of uniaxial strain must hold globally, it need not hold locally owing to grain-grain interactions 178 .…”