Indentation size effect and shear transformation zone size in a bulk metallic glass in two different structural states
- Indentation size effect and shear transformation zone size in a bulk metallic glass in two different structural states
- 최인철; Zhao, Yakai; 김용재; 유병길; 서진유; Ramamurty, Upadrasta; 장재일
- Bulk metallic glass; Nanoindentation; Indentation size effect; Shear transformation zone; Yield strength
- Issue Date
- Acta materialia
- VOL 60, NO 19, 6862-6868
- 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
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