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MM: Metall- und Materialphysik

MM 45: Mechanical Properties III

MM 45.3: Talk

Friday, March 31, 2006, 13:00–13:15, IFW A

High compression strain in bulk metallic glass composites containing low fraction of nanocrystals — •Alban Dubach, Florian Dalla Torre, Marco Siegrist, Kaifeng Jin, and Jörg F. Löffler — Laboratory of Metal Physics and Technology, Department of Materials, ETH Zürich, Wolfgang-Pauli-Str. 10, CH-8093 Zürich, Switzerland

A significant difference in compression strain but a similar yield strength has been measured for Zr-based bulk metallic glasses, if cast using two different techniques (casting via arc melting or induction melting). The processing route via arc melting produces samples showing plastic compression strains of 10-20%, whereas the other generates samples with only 0-2% plasticity. Microstructural analysis shows that despite the good glass-forming ability of the alloys chosen, samples with high compressive strain contain nanosized crystals in a glassy matrix. These samples are x-ray amorphous, while transmission electron microscopy clearly reveals the presence of a low fraction of nanocrystals. In contrast, the samples processed via induction melting are fully amorphous, but less ductile. We suggest that the second-phase nanoparticles, despite their low volume fraction not detectable by x-ray diffraction, lead to nucleation and multiplication of shear bands, in turn producing high plastic strain. Such high plasticity allows ’in-situ’ probing of deformation kinetics by cycling the strain rate during compression testing. Results show a negative strain-rate sensitivity, which tends to be more pronounced for samples containing a higher fraction of second-phase particles or tested at higher strain rates.