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

Title
Indentation size effect and shear transformation zone size in a bulk metallic glass in two different structural states
Authors
최인철Zhao, Yakai김용재유병길서진유Ramamurty, Upadrasta장재일
Keywords
Bulk metallic glass; Nanoindentation; Indentation size effect; Shear transformation zone; Yield strength
Issue Date
2012-11
Publisher
Acta materialia
Citation
VOL 60, NO 19, 6862-6868
Abstract
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 ~25 atoms, which increases 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.
URI
http://pubs.kist.re.kr/handle/201004/43299
ISSN
13596454
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KIST Publication > Article
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