Dresden 2014 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 32: Transport II - Microstructure/Grain boundaries
MM 32.2: Talk
Tuesday, April 1, 2014, 16:00–16:15, IFW B
Transport and structural properties of grain boundaries in ultrafine grained Cu — •Matthias Wegner1, Jörn Leuthold1, Martin Peterlechner1, Daria Setman2, Michael Zehetbauer2, Sergiy V. Divinski1, and Gerhard Wilde1 — 1Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Straße 10, D-41849, Germany — 2Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Wien, Austria
According to existing models of grain refinement by severe plastic deformation, the abundance of lattice dislocations created during the severe straining serves to modify the grain boundary structure of general high angle grain boundaries (GHAGB) towards a state with an enhanced excess free energy density. The hereby modified microstructure of 4N Cu, processed by High Pressure Torsion (HPT), tends to recrystallize already at low homologous temperatures of about 0.26 revealing a significant decrease in the recrystallization temperature. Diffusion in these structures features "ultra fast" in addition to "conventional" rates of grain boundary diffusion along GHAGB (as present in annealed coarse-grained polycrystals). The results indicate a special microstructural state of at least a fraction of interfaces (suitable for percolation) which relax, but are still observable at 320 K. Diffusion experiments above 320 K involve a complete recrystallization of the initial structure. Fast diffusion rates are still measurable featuring the presence of "High Energy Grain Boundaries" (HEGB) in recrystallized HPT Cu. At temperatures higher than 443 K, microstructural relaxation induces a further transformation of HEGB into GHAGB.