Application Of High-pressure Torsion Research Articles

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

Abstract 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.

Application of High Pressure Torsion to Bulk Samples

High pressure torsion (HPT) is a well-known procedure to impart severe plastic deformation (SPD) into metallic materials. It was reported that HPT produces grain sizes finer than those using other SPD processes such as equal-channel angular pressing (ECAP). However, the application of HPT has been restricted to thin disk samples. In this study, an HPT process was developed for use with bulk samples. This process is designated as Bulk-HPT for comparison with conventional Disk-HPT. Cylindrical samples of an Al-3%Mg-0.2%Sc alloy having dimensions of 10 mm in diameter and 8.6 mm in height were prepared for Bulk-HPT. The samples were strained under a pressure of 1 GPa for 2 turns at room temperature. Microstructural observations revealed that the samples contained regions having a grain size of ~130 nm. Tensile testing showed a superplastic ductility ~480 % at 673 K with an initial strain rate of 3.3x10-2 s-1.