Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 29: Mechanical Properties I
MM 29.4: Vortrag
Mittwoch, 27. Februar 2008, 14:45–15:00, H 0111
In situ tensile testing of nanocrystalline Pd and Pd-Ag alloys — •Kejing Yang1, Julia Ivanisenko2, Jürgen Markmann3, and Hans-Jörg Fecht1,2 — 1Institute of Micro and Nanomaterials, University of Ulm, D-89081 Ulm, Germany — 2Institut für Nanotechnologie, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany — 3Universität des Saarlandes, FR7.3 Technische Physik, Saarbrücken, Germany
Arising from a low strain hardening ability, the limited uniform elongation of nanocrystalline materials (NC) hinders the further improvement of their mechanical properties. In this study we suggest a way to enhance strain hardening by purposefully alloying Pd to reduce its stacking fault energy (SFE). Nanocrystalline Pd and Pd-Ag alloys were prepared by high-pressure torsion. Tensile testing was carried out in situ in a high-resolution SEM to investigate the mesoscopic deformation process at a strain rate of 10-3 s-1. The NC alloys demonstrated very high values of strength and ductility. The true stress-true strain curves exhibit a larger strain hardening effect and larger uniform deformation in Pd-Ag alloys than in pure Pd. We relate this enhanced behavior to a decreased SFE in the alloys: the lower the SFE, the more difficult is the cross slip and climb of split dislocations, which leads to greater dislocation storage and, ultimately, to increased strain hardening. The dimpled structure of fracture surfaces in the alloys will also be discussed in relationship to these findings.