Dynamic compression-induced twins and martensite and their combined effects on the adiabatic shear behavior in a Ti-8.5Cr-1.5Sn alloy

The samples cut from the Ti-8.5Cr-1.5Sn titanium alloy were prepared to explore the combined effects of dynamic compression-induce twins and martensite on the adiabatic shear behavior. The morphologies of the deformed microstructures were examined by means of optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) observations, which revealed a high density of twins and martensite. The volume fraction of these features increased when the strain rate increased from 1000/s to 1500/s, owing to the relatively large driving force associated with twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) effects. Such phenomena resulted in an increase in the unit strain increment (induced by the unit stress increment Delta epsilon / Delta sigma) and the energy absorbed. At strain rates of 2000/s or higher, adiabatic shear failure occurred and the values of Delta epsilon / Delta sigma and the absorbed energy were far greater than that at 1500/s. The twins and martensite around the adiabatic shear bands (ASBs) were broken due to severe local deformation and subsequent dynamic recrystallization. Furthermore, the presence of twins and martensite induced (in general) bifurcation of the ASBs, which played a crucial role in the plasticity of the alloy.