Deformation twinning in explosively-driven tantalum

Deformation twinning resulting from high explosive-driven shock and associated plasticity was investigated in high-purity b.c.c. tantalum. Post mortem characterization of samples shocked at relatively higher and lower pressures showed significant {112}〈111〉 twin activity. Further analysis of the lower shock pressure sample showed twins to be spatially clustered at the mesoscale, indicating the role of twin termination at grain boundaries to produce requisite twin initiation stresses in neighbor grains. In addition, analysis of electron backscatter diffraction data suggests that twin propagation across boundaries does not require minimal misorientations between the active variants of the twins in adjacent parent grains. A minimum threshold grain size of approximately 25 μm was determined for both samples, below which twinning was suppressed. Finally, the observation of spall voids at twin intersections implied that twinning increases the density of preferred damage initiation sites during the shock deformation process. Overall, twinning was shown to play a significant role in the deformation and damage evolution of shock-loaded tantalum.