Severe plastic deformation in Gum Metal with composition at the structural stability limit

The effects of severe plastic deformation on the mechanical properties and deformation behavior of Gum Metal with a nominal composition of Ti-36Nb-2Ta-3Zr-0.3O (mass.%) were investigated using high-pressure torsion (HPT). Applying the HPT process, the alloy shows ultra-low Young's modulus, high strength, extended elastic limit, high ductility, and very low hardening during HPT. The tensile strength of Gum Metal increases with increasing equivalent strain, while work hardening is much smaller than reported values for other common metallic materials. The deformation structure is composed of ultrafine grains produced by transgranular shear through application of HPT. These results suggest that the strengthening mechanism of Gum Metal is attributable to a unique plastic deformation which operates in the region where the local stress reaches values close to that of ideal strength.