Simulation Study Of Microstructural Evolution During Solidification Process Of Liquid Ca₅₀Zn₅₀Alloy

In this article, a simulation study was performed for the solidification process ofliquid metal Ca₅₀Zn₅₀by adopting a molecular dynamics method. Several analysismethods, including the pair distribution function g（r） curves, the chemical short-rangeorder （CSRO） parameter, the bond-type index method, the cluster-type index method（CTIM-2） and the three-dimensional visualizing, were used to analyze the variationsof microstructure during this solidification process.The rapid solidification processes of liquid metal alloy Ca₅₀Zn₅₀have beensimulated at different cooling rates. The results showed that as the cooling rate wereset as1×10¹⁴K/s﹑1×10¹³K/s﹑1×10¹²K/s﹑5×1011K/s, the amorphous structureswould be formed with icosahedral clusters as the majority clusters in the system. Thecritical cooling rate of crystallization is5×10¹¹K/s. and the icosahedral clustersincreases as the cooling rate decreases. However the cooling rate being1×10¹¹K/s﹑5×10¹⁰K/s, the crystal structures were metastable. the Zn atoms form bcc clusters,and the Ca atoms change into hcp and fcc.The rapid solidification process with the cooling rate of1×10¹³K/s of a systemcontains₅₀00Ca and₅₀00Zn atoms was simulated. Here we studied thecharacteristic of short-range and medium-range order of this system. We discoveredthat the pair distribution function curve unlike normal ones. The discrepancy betweenthe atomic radius of Ca and Zn causes first peak of pair distribution function curvesplitting into three small ones. Majority center atoms of clusters are Zn and thecoordination number between9-12. The majority of clusters is icosahedrons, and itsnumber change is the most obvious one. majority clusters are linked byvertex-sharing（VS）、edge-sharing（ES） and face-sharing（FS） atoms at high temperature,and big clusters are linked by intercross-sharing （IS） atoms.