Dresden 2006 – scientific programme
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MM: Metall- und Materialphysik
MM 37: Nanostructured Materials I
MM 37.3: Talk
Thursday, March 30, 2006, 15:15–15:30, IFW D
The role of dislocations during deformation of nanocrystalline metals — •Jürgen Markmann1,2 and Jörg Weissmüller1,2 — 1Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft, Postfach 3640, 76021 Karlsruhe — 2Universität des Saarlandes, FR 7.3 Technische Physik, Postfach 151150, 66041 Saarbrücken
During deformation of nanocrystalline metals various deformation mechanisms can be activated. Depending on the applied strain rate and size of the grains grain boundary diffusion, i.e. Coble creep, grain boundary sliding, and even grain rotation contribute to the material transport. Despite the fact that standard dislocation sources of the Frank-Read type in the interior of nano grains cannot be activated before the material fails, it has been shown that dislocations are active in nanocrystalline metals. Here the microstructure of nanocrystalline palladium after a true strain of є≈ 0.3 to 0.7 deformed by cold rolling at strain rates є between 0.08 s−1 and 0.3 s−1 was investigated. With increasing strain rate the stacking fault density decreases while the number of twins notedly increases as shown by HRTEM images. The number of discovered lattice faults especially after deformation at higher strain rates implies dislocation motion as the main and dominant mechanism of deformation. This means that the number of dislocations is a function of the applied strain rate or stress rather than a function of the strain or total deformation of the material. Furthermore the possibilities of nucleation of dislocations from grain boundaries as proposed by theory and the nucleation of a complete dislocation loop inside the grain are shortly discussed.