Mechanisms of plastic deformation and shock-induced phase transformation in natural and synthetic single crystal scheelite

Dynamic response of natural, [0 0 1]-oriented, and synthetic, [2 0 1]-oriented, scheelite (CaWO4) was studied in planar impact experiments with shock up to 20 GPa. The velocity of the interface between the sample and the PMMA window was continuously monitored by VISAR. Although the waveforms recorded in the planar impact experiments revealed different dynamic responses of the two materials, the plastic deformation in both cases is governed by the dislocation glide in {112} planes with resolved shear stress of similar to 0.6-0.7 GPa. The waveform obtained from [0 0 1]-oriented material contains the signature of the second-order scheelite-fergusonite transformation. The absence of the transformation signature in the waveforms obtained after strong impact of [2 0 1]-oriented crystals is probably due to faster transformation kinetics under loading in this direction.