On the mechanism and the length scales involved in the ductile fracture of a bulk metallic glass

Tandaiya, Parag and Narasimhan, R and Ramamurty, U (2013) On the mechanism and the length scales involved in the ductile fracture of a bulk metallic glass. In: Acta Materialia, 61 (5). pp. 1558-1570.

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Abstract

Some bulk metallic glasses (BMGs) exhibit high crack initiation toughness due to shear band mediated plastic flow at the crack tip and yet do not display additional resistance to crack growth due to the lack of a microstructure. Thus, at crack initiation, the fracture behavior of BMGs transits from that of ductile alloys to that of brittle ceramics. In this paper, we attempt to understand the physics behind the characteristic length from the notch root at which this transition occurs, through testing of four-point bend specimens made of a nominally ductile Zr-based BMG in three different structural states. In the as-cast state, both symmetric (mode I) and asymmetric (mixed mode) bend specimens are tested. The process of shear band mediated plastic flow followed by crack initiation at the notch root was monitored through in situ imaging. Results show that stable crack growth occurs inside a dominant shear band through a distance of, similar to 60 mu m, irrespective of the structural state and mode mixity, before attaining criticality. Detailed finite element simulations show that this length corresponds to the distance from the notch root over which a positive hydrostatic stress gradient prevails. The mean ridge heights on fractured surfaces are found to correlate with the toughness of the BMG. The Argon and Salama model, which is based on the meniscus instability phenomenon at the notch root, is modified to explain the experimentally observed physics of fracture in ductile BMGs. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Item Type:	Journal Article
Publication:	Acta Materialia
Publisher:	Elsevier Science
Additional Information:	Copyright of this article belongs to Elsevier Science.
Keywords:	Metallic Glass; Ductile Fracture; Fracture Mechanism; Shear Band; Length Scale
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	11 Apr 2013 05:31
Last Modified:	11 Apr 2013 05:31
URI:	http://eprints.iisc.ac.in/id/eprint/46309

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