Generation of extreme grain aspect ratios in severely deformed tantalum at elevated temperatures

Severe plastic deformation effectively produces nanostructured metals. During deformation these structures undergo repetitive dynamic recovery processes, limiting refinement and aspect ratio. Processing tantalum at elevated temperatures by high pressure torsion allows the synthesis of structures with extreme grain aspect ratios of almost ten. Although the overall restoration processes increase with deformation temperature, reflected in enlarged lamellae thicknesses, they are not effective enough to reduce the lamella length at elevated temperatures. Our results indicate that triple junction motion is impeded below a certain temperature while the efficiency of deformation-induced boundary migration diminishes with temperature, allowing to generate such elongated structures. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.