Berlin 2012 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 3: Topical Session Bulk Nanostrucured Materials I - Processing

MM 3.5: Vortrag

Montag, 26. März 2012, 11:30–11:45, H 0107

Effect of hydrostatic pressure on the microstructure and mechanical properties during and after high pressure torsion — •Erhard Schafler, Roman Schuster, Michael Kerber, and Florian Spieckermann — Universität Wien, Fakultät für Physik, Physik Nanostrukturierter Materialien

The hydrostatic pressure is a general feature of severe plastic deformation (SPD) methods, especially when performing high pressure torsion (HPT). It is essential for achieving the high strains and to introduce the high amount of lattice defects, which are necessary for the fragmentation into an ultra-fine grained materieal. The investigations of HPT-processed Cu and Ni under variation of the hydrostatic pressure revealed marked differences between the in-situ torsional stress (torque measurement) and the post-HPT flow stress of the ultrafine-grained materials. A special experimental procedure was designed to simulate the hydrostatic pressure release, in order to gain insight into the processes behind unloading. Investigations by X-ray line profile analysis and hardness measurement show marked influences of the pressure release on microstructure and strength. While the size of the coherently scattering domains indicate that the fragmentation process is already finished during the HPT-deformation, the dislocation density decreases drastically and the arrangement of the dislocations within the subgrain structure changes to a less stress-intensive one, upon pressure release. In parallel the hardness decreases significantly and confirms the discrepancy between in-situ torque-stress and post-HPT flow stress. Work supported by the Austrian Science Fund, project S 10403