Cooling rate dependence of simulated Cu64.5Zr35.5 metallic glass structure

Using molecular dynamics simulations with embedded atom model potential, we study structural evolution of Cu_64.5Zr_35.5 alloy during the cooling in a wide range of cooling rates γ ∈ (1.5 ṡ 10⁹, 10¹³) K/s. Investigating short- and medium-range orders, we show that the structure of Cu_64.5Zr_35.5 metallic glass essentially depends on cooling rate. In particular, a decrease of the cooling rate leads to an 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 γ_min = 1.5 ṡ 10⁹ K/s. Analysing the structure of the glass at γ_min, we observe the formation of nano-sized crystalline grain of Cu₂Zr intermetallic compound with the structure of Cu₂Mg Laves phase. The structure of this compound is isomorphous with that for Cu₅Zr intermetallic compound. Both crystal lattices consist of two types 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 of Cu-Zr system and explains the drastic increase of the abundances of these clusters observed at γ_min.