A new designed incremental high pressure torsion process for producing long nanostructured rod samples

High pressure torsion (HPT) is one of the most important and effective severe plastic deformation (SPD) processes for producing nanostructured (NS) and ultrafine grained (UFG) metals. Whereas HPT presents excellent mechanical properties, its applications are limited to small disk-shaped samples. In this study a new design of incremental HPT (IHPT) process entitled SIHPT is developed which is much convenient for the production of large NS and UFG metallic rods. In this new design, some steppers along the length of the rod-shaped sample are used while applying an axial load from two ends of it. Step twisting of stepper parts with simultaneous axial loads extend the deformed region to the whole length of the sample. The five turn IHPT process was applied to a 50 mm length and 10 mm diameter pure copper sample and microstructure, and mechanical properties were evaluated. The microstructural study of SIHPT processed samples using TEM and EBSD micrographs clearly reflected the NS sample having an average grain size of less than 100 nm. Also, microhardness measurements showed that the sample has fairly good homogeneity through both axial and radial directions. Besides, tensile test measurements indicate that there is about four times improvement in yield strength of nanostructured sample compared to unprocessed metal which is accompanied with satisfactory ductility as a result of high hydrostatic compressive stresses.