Berlin 2015 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 40: Nanomaterials II: Mechanical Properties
MM 40.3: Vortrag
Mittwoch, 18. März 2015, 16:15–16:30, H 0107
Aspects of universal yield behavior of bulk metallic glasses unraveled in nanocrystalline Pd-Au alloys — •Andreas Leibner, Christian Braun, Jonas Heppe, Manuel Grewer, and Rainer Birringer — Universität des Saarlandes, FR7.2 Experimentalphysik, Campus D2 2, 66123 Saarbrücken
We present experimental evidence that plastic yielding of nanocrystalline (NC) metals at the low end of the nanoscale is reminiscent of universal yield behavior of metallic glasses. NC Pd-Au samples with a grain size of D 10 nm and isotropic microstructure were deformed under different conditions:
From strain-rate dependent deformation studies on shear-compression-specimens, we find that the energy barrier height of NC Pd90-Au10 exhibits universal scaling behavior Δ G ∝ Δ τ3/2 [1], where Δ τ is a residual load, giving rise to a generalization of the Johnson-Samwer T2/3 scaling law [2] of yielding in metallic glasses. Additionally, we use microhardness as measure for the shear yield stress of Pd-Au samples with different Au-concentrations (and concomitantly different elastic moduli). As a result, the NC alloys exhibit the linear correlation τy / G = 0.00267 ± 0.002 discovered for over 30 bulk metallic glasses [2]. Since shear transformations are considered to be the generic flow defect in metallic glasses, it seems reasonable to suppose that shear softening of grain boundaries provokes the occurrence of shear transformations.
M. Grewer and R. Birringer, PRB 89, 184108 (2014)
W.L. Johnson and K. Samwer, PRL 95, 195501 (2005)