Dependence of the titanium structure formed under high-rate loading on its initial state

The structure of titanium specimens with different grain sizes and initial defect density that were subjected to large high-rate strains is studied, and the critical parameters of the onset of an unstable plastic flow in the specimens are determined. It is established that the formation of a titanium structure and the critical parameters governed by this structure are determined mainly by twinning. Twinning in shock-loaded titanium is the mechanism of plastic deformation that ensures the minimum change in the internal energy. Twinning in titanium under high-rate strain develops at the earlier stages over all admissible twinning systems and results in fragmentation of the structure. The twins are not the structural elements that contribute to the evolution of a uniform plastic strain. Fragmentation of the structure in the formation of twins decreases the critical parameters of the onset of an unstable plastic flow. It is found that as the strain increases, the twins fill the material up to a certain limit level, after which energy relaxation occurs owing to the formation of adiabatic-shear bands and/or cracking. The titanium structure formed in the deformation is highly stable.