Matching Glass-Forming Ability with the Density of the Amorphous Phase
Y. Li1,2*,
Q. Guo1,2,
J. A. Kalb1,3
and
C. V. Thompson1,3*
1 Singapore–Massachusetts Institute of Technology (MIT) Alliance, 4 Engineering Drive 3, Singapore 117576.
2 Department of Materials Science and Engineering, National University of Singapore, 7 Engineering Drive 1, Singapore 117576.
3 Department of Materials Science and Engineering, MIT, Cambridge, MA 02139, USA.
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Fig. 1. Layer structure of a microcantilever with a fixed support (side view). A thin film of amorphous Cu-Zr (thickness 128 ± 4 nm) was deposited on the SiN (thickness 216 ± 3 nm). A thin Pt capping layer (thickness 15 ± 5 nm) was used to prevent oxidation of the Cu-Zr film during annealing. The thicknesses of the layers are not drawn to scale.
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Fig. 2. Scanning electron microscopy images of 5-µm–by–30-µm cantilevers before and after furnace crystallization of the Cu-Zr film. (A) Before crystallization. The cantilevers have an initial downward deflection of 3.0 ± 0.5 µm after sputter deposition, due to a compressive stress in the as-deposited Cu-Zr films. (B) After crystallization. The cantilevers curve up by 7.0 ± 0.5 µm due to the development of a tensile stress upon crystallization of the amorphous Cu-Zr films. (C) Schematic side view of the cantilever after the Cu-Zr film has been crystallized. The cantilever curves up with radius r, which is accompanied by a vertical deflection  .  is the central angle corresponding to the curvature. L0 is the total length of the cantilever.
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Fig. 3. Density change upon crystallization ( c – a)/a (A), and the critical thickness for glass formation (B) versus Zr content (atomic %). The density change axis is inverted, to make the two plots more directly comparable. The error of the composition measurement (A) is estimated to be ±1.0 atomic %. In the wedge-casting experiments (B), the error of the critical thickness measurement is ±0.04 mm, and the variation of the composition can be controlled within ±0.05 atomic %
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Fig. 4. Density plot for different compositions in the binary Cu-Zr system. The density of the crystalline phase (estimated from the equilibrium phase diagram using the lever rule), the density of the amorphous phase (estimated from the density change upon crystallization in the present study and the density of the crystalline phase), and density data for Cu-Zr metallic glasses reported in the literature (25, 30–32) are shown.
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