Dislocation density in copper and tantalum subjected to shock compression depending on loading parameters and original microstructure

The dislocation density ρ in copper and tantalum specimens with various grain size that remained after high-strain-rate loading by shock and quasi-isentropic waves with amplitudes of 20–100 GPa has been studied using X-ray diffraction analysis. The deformation rate was 106–109 s−1. It has been confirmed that high-strain-rate loading generates a higher dislocation density in copper than does quasi-static deformation, as well as that the shock-wave loading generates a higher dislocation density than quasi-isentropic loading. In copper, a maximum of ρ has been found in the pressure range of P = 30–40 GPa, which corresponds to a degree of deformation of 0.25–0.3, followed by a drop. This drop in ρ is explained by the partial annealing of defects during adiabatic heating resulting from compression. An increase in ρ in copper with decreasing specimen temperature has been noted. In tantalum, an increase in the shock wave pressure leads to a monotonic increase in the dislocation density. No effect of heating on the annealing of defects in tantalum has been found, even under the maximum pressure. As the average grain size increases, ρ increases in both copper and tantalum.