Cryoforged nanotwinned titanium with ultra-high strength and ductility

Instruments used

EDAX^® Hikari EBSD system and EDAX OIM Analysis™ software

Background

Titanium has the highest strength-to-weight ratio of all metals. Traditionally, the strength of titanium has been improved through alloying, which comes at the expense of reduced ductility and a higher cost associated with the alloying elements. Alternatively, strength can be improved through grain size refinement. In this work, cryoforging was used to reduce the effective grain size by introducing a high density of twin boundaries through repeated gentle uniaxial compression along the principal axes of cuboid-shaped samples at liquid nitrogen temperatures. Twin boundaries are beneficial due to the coherent nature of the grain boundary geometry, which allows for both blocking and transmission of dislocations during deformation. This enhances both the strength and ductility of the material. The approach also preserves the initial grain structure rather than elongating the grains in one direction. Compared with random high-angle grain boundaries, twin boundaries are lower energy boundaries and have reduced mobility. The result is greater stability at higher temperatures, allowing for retention of properties in elevated temperature applications.