Atomic-Scale Heterogeneity of a Multicomponent Bulk Metallic Glass with Excellent Glass Forming Ability

We report the atomic structure of a multicomponent ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$ bulk metallic glass investigated by state-of-the-art experimental and computational techniques. In comparison with a binary ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ metallic glass, Zr-rich interpenetrating clusters centered by paired and stringed Ag atoms and Cu-rich icosahedra are widely observed in the ternary ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$ alloy. The atomic-scale heterogeneity caused by chemical short- and medium-range order is found to play a key role in stabilizing the liquid phase and in improving the glass forming ability of the multicomponent alloy.

Figure 1

Experimental EXAFS spectra from glassy ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$, ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$ and ${\mathrm{Cu}}_{40}{\mathrm{Zr}}_{40}{\mathrm{Ag}}_{20}$ alloys. (a) and (b) EXAFS spectra $k^2\chi (k)$ of ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$, ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$, and ${\mathrm{Cu}}_{40}{\mathrm{Zr}}_{40}{\mathrm{Ag}}_{20}$ for Cu-$K$ and Zr-$K$, respectively; (c) and (d) The Fourier transforms of the Cu-$K$ and Zr-$K$ edges from ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$, ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$ and ${\mathrm{Cu}}_{40}{\mathrm{Zr}}_{40}{\mathrm{Ag}}_{20}$, respectively.

Figure 2

EXAFS spectra $k^2\chi (k)$ of ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$ and corresponding Fourier transforms at (a) Cu-$K$, (b) Zr-$K$, and (c) Ag-$K$ edges obtained experimentally (blue lines) and by model calculations using 300 K ab initio configuration (red lines).

Figure 3

(a) 3D atomic configuration of ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$ predicted by ab initio MD simulations. The bronze, green and light blue balls represent Cu, Zr, and Ag atoms, respectively. (b) The fraction of dominant polyhedra centered by Zr atoms, (c) Cu atoms, and (d) Ag atoms. The blue, red, and green bars represent the results of ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$, ${\mathrm{Cu}}_{45}{\mathrm{Zr}}_{45}{\mathrm{Ag}}_{10}$, and ${\mathrm{Cu}}_{40}{\mathrm{Zr}}_{40}{\mathrm{Ag}}_{20}$, respectively, and the polyhedra are indexed by Voronoi indices.

Figure 4

Ag-centered interpenetrating cluster and corresponding EXAFS spectra. (a) An interpenetrating cluster with paired Ag atoms in the center; (b) EXAFS spectra $k^2\chi (k)$ of Ag-$K$ edges from experiment and from the interpenetrating cluster shown in (a); (c) Fourier transform of Ag-$K$ edge EXAFS spectra $k\chi (k)$; and (d) a large interpenetrating clusters centered by stringed Ag atoms. The red line denotes Ag-Ag connections, and the bronze, green, and light blue balls represent Cu, Zr, and Ag atoms, respectively.