Abnormal strain hardening in nanostructured titanium at high strain rates and large strains

Commercial purity nanostructured titanium prepared by equal channel angular pressing plus cold rolling (grain size ~260 nm) exhibits a nonnegligible strain hardening behavior at large compressive strains (>15%) and quasistatic loading conditions. The degree of the strain hardening increases with increasing strain rates and becomes more pronounced at dynamic loading rates. This behavior is in contrast with what we have seen so far in other nanostructured materials, where flat stress-strain curves are often seen. It was concluded from transmission electron microscopy investigations that in addition to dislocation slips, deformation twinning may have played a significant role in plastic deformation of nanostructured Ti. The structural failure behavior is in-situ recorded by a CCD camera and reasoned according to the microscopic observations.