Molecular Dynamics Simulation Of Medium Range Order Of Metallic Glass

In recent years,metallic glasses have received a lot of attention due to their excellent physical and mechanical properties.These excellent properties are related to its structure.Understanding the atomic arrangement of metallic glasses is still a challenging topic.It is generally believed that the arrangement of metallic glass atoms has a topological and chemical order in short and medium ranges,but not in long range.The icosahedral cluster is regard as the basic local structure unit in short range order,which have high packing efficiency and five order symmetry.Icosahedral clusters can hinder the formation of crystals and improve the glass forming ability.However,the structure origin for the high glass forming ability of metallic glass is still unclear.Several medium range order models for metallic glasses has been proposed including the efficient cluster packing(ECP)mode and the Bergman packing.These two models describe the process from the atomic and cluster perspectives,respectively.In this paper,we introduce the research background,structural characteristics and development of metallic glasses.The rapid quenching processes of Zr₈₀Pt₂₀and Cu₄₇Zr₄₇Al₆alloy is investigated by using molecular dynamics simulation method.Atomic bonding and icosahedral clusters in short range order are investigated by radial distributional functions,Voronoi tessellation method and coordination numbers.We found that the main short range order in these two alloys are prefect icosahedral and distorted icosahedral.These ICO clusters are connection with each other by vertex sharing,edge sharing,face sharing and interpenetrating sharing forming medium range order clusters.For the medium range order,we analyze the arrangement of atoms investigated by radial distributional functions and angle distributional functions.In order to understand the atomic arrangement in the medium range,we developed a structure analysis method—sharing coordination atoms,which can better distinguish whether the atoms packed in Bergman or Mackay order.The results show that the atoms in both Zr₈₀Pt₂₀and Cu₄₇Zr₄₇Al₆packed in Bergman method.We picked all the center atoms of icosahedral in both systems to analysis their packing pattern.We found that in both the binary alloy Zr₈₀Pt₂₀and the ternary alloy Cu₄₇Zr₄₇Al₆,these atoms in the short range order are packed in the icosahedral method and in medium range order are packed in the Bergman method.We find a novel medium range order structure,in which the icosahedral clusters packed in the Bergman method,exists in the glass.This new cluster,with the size of 1.2-1.4nm and high degree of five-symmetry order,will contribute to the high glass forming ability.