Regensburg 2019 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 36: Liquid and Amorphous Metals

MM 36.8: Vortrag

Donnerstag, 4. April 2019, 12:15–12:30, H46

Size-dependent failure of the strongest bulk metallic glass — •Ruitao Qu^1,2, Dominik Tönnies¹, Lin Tian¹, Zengqian Liu², Zhefeng Zhang², and Cynthia Volkert¹ — ¹Institute of Materials Physics, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany — ²Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, China

Upon reducing sample size into the sub-micrometer scale, the mechanical behavior of metallic glasses (MGs) is often changed dramatically. For instance, obvious tensile ductility and necking can be observed in nano-scale MGs, while they are rarely seen in bulk samples. Here we present our recent studies on the size effect of the deformation and failure behaviour of a Co-based MG, which exhibits the highest strength among all known bulk MGs. An obvious brittle-to-ductile transition accompanied by a drastic change of failure mode were observed on decreasing the sample size. The bulk compressive samples failed by splitting and shattering, similar to other brittle MGs, while the micrometer and sub-micrometer scale specimens demonstrated shear banding, typical of ductile MGs. In order to assess whether this size effect was caused by the reduced probability of the presence of defects in small-scale samples, we intentionally designed various micropillar specimens containing defects. However, no brittle failure was observed in the defective micropillars, even though the local maximum tensile stress in front of defects had far exceeded the critical tensile stress for splitting in bulk sample. A characteristic distance model for cleavage cracking initiation in brittle MGs is proposed to explain these observations.