Cooling rate dependence of simulated ${\rm Cu_{64.5}Zr_{35.5}}$ metallic glass structure

Abstract

Using molecular dynamics simulations with embedded atom model potential, we study structural evolution of ${\rm Cu_{64.5}Zr_{35.5}}$ alloy during the cooling in a wide range of cooling rates $\gamma\in(1.5\cdot 10^{9},10^{13})$ K/s. Investigating short- and medium-range order, we show that structure of ${\rm Cu_{64.5}Zr_{35.5}}$ metallic glass essentially depends on cooling rate. In particular, a decrease of the cooling rate leads to a increase of abundances of both the icosahedral-like clusters and Frank-Kasper Z16 polyhedra. The amounts of these clusters in the glassy state drastically increase at the $\gamma_{\rm min}=1.5\cdot 10^{9}$ K/s. Analysing the structure of the glass at $\gamma_{\rm min}$, we observe the formation of nano-sized crystalline grain of ${\rm Cu_2Zr}$ intermetallic compound with the structure of ${\rm Cu_2Mg}$ Laves phase. The structure of this compound is isomorphous with that for ${\rm Cu_5Zr}$ intermetallic compound. Both crystal lattices consist of two type of clusters: Cu-centered 13-atom icosahedral-like cluster and Zr-centered 17-atom Frank-Kasper polyhedron Z16. That suggests the same structural motifs for the metallic glass and intermetallic compounds and explains the drastic increase of the abundances of these clusters observed at $\gamma_{\rm min}$.