{332}(113) twinning in a 6-type Ti-Nb alloy over a wide range of strain rates

The {332}(113) twinning in a 6-type Ti-25Nb alloy is investigated quantitatively at 10% compression strain over a wide range of strain rate from 10-2 s-1 to 106 s-1, using material testing system, split Hopkinson pressure bar, and gas gun loading. Electron backscatter diffraction data are collected from the postmortem samples to obtain activated twinning systems and twinning strain tensors. With increasing strain rate, yield stress and twin density increase, and twin thickness decreases. At low strain rate, only the twinning systems with high Schmid factor can be activated to form thick twins. However, at medium and high strain rates, certain twinning activation deviates from the Schmid law, and twin thickening is relatively insensitive to Schmid factor. Twinning strain is the highest for the matrix grain orientations near (114), but approximately zero for the orientations near (111). Contribution of twinning to plastic strain at medium strain rate is significantly higher than those at low and high strain rates.