Temperature-mediated extraordinary rate insensitivity of strongly textured titanium

Strain rate sensitivity is a critical parameter influencing mechanical behaviors, typically resulting in increased flow stress at higher strain rates across most metallic materials. In the present study, we report an unusual phenomenon of strain rate insensitivity in hexagonal titanium deformed at 77 K, independent of strain rates ranging from 0.001 to 0.1 s⁻¹. Through detailed characterization using synchrotron Laue microdiffraction, transmission electron microscopy, and in situ electron backscatter diffraction, we attribute this unusual behavior to the consistency in the type and density of defects. Specifically, at the yield stage, strain rate insensitivity is linked to the prevalence of <a> dislocations, while the insensitivity during initial deformation stages correlates with the dynamics of dislocations and twins both of which are evolved in concert. These findings not only provide new insights into cryogenic deformation theory, but also identify new challenges and prospects for the development of high-speed cryogenic forming or extrusion.