2015-Sustainable Industrial Processing Summit
SIPS 2015 Volume 1: Aifantis Intl. Symp. / Multiscale Material Mechanics
| Editors: | Kongoli F, Bordas S, Estrin Y |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2015 |
| Pages: | 300 pages |
| ISBN: | 978-1-987820-24-9 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Exploring the Size-Induced Brittle-To-Ductile Transition in Small-Scale Metallic Glasses with Gradient Plasticity Models
Dominik Toennies1; Cynthia A. Volkert1; Robert Maass1;1INSTITUTE OF MATERIALS PHYSICS, UNIVERSITY OF GOETTINGEN, Goettingen, Germany (Deutschland);
Type of Paper: Regular
Id Paper: 206
Topic: 1
Abstract:
Plastic deformation of metallic glasses is known to depend on several intrinsic and extrinsic parameters, such as mechanical strain, temperature, deformation rate, structure, sample size and composition. In recent studies, the size-dependent deformation behavior of small-scale Pd77Si23 metallic glass samples was investigated by micro compression testing of FIB-made pillars in the size range of 200--2000 nm in diameter. A size- and rate-dependent brittle-to-ductile transition during room temperature deformation was demonstrated by showing that pillars deform in an apparently homogeneous manner when they are either smaller than a critical value in diameter, or when they are tested at very low applied rates. A careful analysis of shear band patterns in SEM micrographs of pillars above the critical size reveals that the shear band spacing scales with sample size and the brittle-to-ductile transition can be explained by a geometric overlap of neighbored shear bands due to a reduction of their spacing below the typical shear band thickness of ~15 nm. However, since the strain rate sensitivity exponent remains unchanged at a value of about 0.05 regardless of sample size, deformation rate, and apparent deformation mode, it is concluded that the underlying atomistic mechanism remains the same through the brittle-to-ductile transition. The work is now extended in order to explore the physical reasons behind the scaling of the shear band spacing with size. Gradient plasticity models have successfully explained a similar scaling behavior of shear bands in nano-crystalline materials in the past. Here, we present the first results regarding the applicability of gradient plasticity models to explain the compression behavior of small scale specimens of metallic glasses.