Laser shock compression of copper and copper–aluminum alloys

Copper and copper aluminum (2 and 6 wt% Al) with orientations [0 0 1] and [1 3 4] were subjected to high intensity laser shocks (energy levels of 40–300 J; energy densities of 15–70 MJ/m2 and durations below 10 ns). In situ X-ray diffraction and VISAR wave profile measurements were used to study the response of the lattice to the shock. Recovered samples were characterized by transmission electron microscopy in order to study the defects within the lattice. The results are rationalized in terms of a criterion in which slip and twinning are considered as competing mechanisms. The slip-twinning transition is determined quantitatively and predicted as a function of orientation, temperature, and stacking fault energy (determined by the Al content of the alloy). A constitutive description is applied to the two orientations and differing compositions, incorporating both slip and twinning in terms of orientation, stacking fault energy, temperature, and strain rate. The threshold stress is calculated, considering the effect of shock heating. The constitutive description provides calculated thresholds in pure copper: 18 GPa for [0 0 1] and 25 GPa for [1 3 4]. The experimentally determined threshold twinning stress for pure copper in the [0 0 1] orientation is 25 GPa, whereas the one for the [1 3 4] orientation is between 40 and 60 GPa. The predictions are in agreement with experiments. It also provides thresholds for the Cu–Al alloys.