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Indentation size effect and shear transformation zone size in a bulk metallic glass in two different structural states

Choi, In-Chul and Zhao, Yakai and Kim, Yong-Jae and Yoo, Byung-Gil and Suh, Jin-Yoo and Ramamurty, Upadrasta and Jang, Jae-il (2012) Indentation size effect and shear transformation zone size in a bulk metallic glass in two different structural states. In: ACTA MATERIALIA, 60 (19). pp. 6862-6868.

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Official URL: http://dx.doi.org/10.1016/j.actamat.2012.08.061


The existence of an indentation size effect (ISE) in the onset of yield in a Zr-based bulk metallic glass (BMG) is investigated by employing spherical-tip nanoindentation experiments. Statistically significant data on the load at which the first pop-in in the displacement occurs were obtained for three different tip radii and in two different structural states (as-cast and structurally relaxed) of the BMG. Hertzian contact mechanics were employed to convert the pop-in loads to the maximum shear stress underneath the indenter. Results establish the existence of an ISE in the BMG of both structural states, with shear yield stress increasing with decreasing tip radius. Structural relaxation was found to increase the yield stress and decrease the variability in the data, indicating ``structural homogenization'' with annealing. Statistical analysis of the data was employed to estimate the shear transformation zone (STZ) size. Results of this analysis indicate an STZ size of similar to 25 atoms, which increases to similar to 34 atoms upon annealing. These observations are discussed in terms of internal structure changes that occur during structural relaxation and their interaction with the stressed volumes in spherical indentation of a metallic glass. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to PERGAMON-ELSEVIER SCIENCE LTD, ENGLAND
Keywords: Bulk metallic glass;Nanoindentation;Indentation size effect;Shear transformation zone;Yield strength
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 31 Dec 2012 07:12
Last Modified: 31 Dec 2012 07:12
URI: http://eprints.iisc.ac.in/id/eprint/45587

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