Coupling between chemical and dynamic heterogeneities in a multicomponent bulk metallic glass

We performed molecular-dynamics simulation and predicted a strong coupling between chemical short-range order and dynamic heterogeneity in a multicomponent ${\text{Cu}}_{45}{\text{Zr}}_{45}{\text{Ag}}_{10}$ alloy that possesses excellent glass-forming ability. The intrinsic correlation between the chemical and dynamic heterogeneities leads to significant spatial partitioning and dynamic isolation between Cu-rich slow-dynamics regions and Ag-rich fast-dynamics regions. This characteristic may play an important role in the improved glass-forming ability with Ag addition by retarding crystallization kinetics.

Figure 1

(Color online) (a) Temperature dependence of a fraction of dominant Voronoi polyhedra centered by Cu atoms in ${\text{Cu}}_{45}{\text{Zr}}_{45}{\text{Ag}}_{10}$ during cooling from 2500 to 300 K. The average number of Ag atoms in Ag-chained clusters is also plotted against temperature. (b) Cross section of atomic structure of glassy ${\text{Cu}}_{45}{\text{Zr}}_{45}{\text{Ag}}_{10}$ at 300 K. The bronze (light gray in printed version) and dark blue (dark gray) balls represent Cu and Ag atoms, respectively. The Cu atoms center the polyhedra with a Voronoi index $⟨0,0,12,0⟩$. Zr atoms are not shown in order to clearly illustrate the chemical heterogeneity.

Figure 2

(Color online) (a) Self-intermediate scattering functions of Cu, Zr, and Ag in ${\text{Cu}}_{50}{\text{Zr}}_{50}$ and ${\text{Cu}}_{45}{\text{Zr}}_{45}{\text{Ag}}_{10}$ liquids. (b) Dynamic susceptibility of ${\text{Cu}}_{50}{\text{Zr}}_{50}$ and ${\text{Cu}}_{45}{\text{Zr}}_{45}{\text{Ag}}_{10}$ as function of time.

Figure 3

(Color online) Correlation between atomic mobility of Cu atoms and their local structural environments in ${\text{Cu}}_{45}{\text{Zr}}_{45}{\text{Ag}}_{10}$ at 800 K. The Cu atoms are sorted into 20 groups in the increasing order of their displacement. In each group, the percentage of $⟨0,0,12,0⟩$ polyhedra and the number of coordinated Ag atoms are plotted with (a) a short time interval of $1.5t_{\beta }$ and (b) a long time interval of $1.5t_{\alpha }$. (c) 3D mean-square displacement map of all atoms based on propensity motion for the conditions observed in (b). The isosurfaces indicate the slow- and fast-dynamics regions where $\Delta r^2$ is less than $25{\text{Å}}^2$ (blue regions, dark gray in printed version) and more than $80{\text{Å}}^2$ (green to red regions, light gray to gray), respectively. (d) 3D map showing both isosurfaces of slow-dynamics regions and distribution of Ag atoms (balls). The slow-dynamics regions are apparently Ag-poor regions. The cube has the dimensions of $53\times 53\times 53{\text{Å}}^3$; the color bars shown in (c) and (d) show the range from fast (top) to slow (bottom) dynamics.

Figure 4

(Color online) Distance matrix for (a) the slowest and (b) the fastest Cu atoms categorized in Fig. 3b. Darker squarelike areas in (a) correspond to the atoms that travel a smaller distance and indicate the MB-MB transitions. These transitions are not observed for the fastest Cu atoms.