Molecular Dynamics Simulation Of Rapid Solidification Process Of Metallic Cooper And Cooper-zirconium Alloy Under High Pressure

The development history of theory and technology about liquid metal rapid solidification,the important role of computational simulation in scientific research and industrial production,the application of molecular dynamics（MD）simulation are briefly reviewed in this paper.The commonly used microstructure analysis methods and the definition of the largest standard cluster（La SC）and related structural parameters is then described.Using MD simulation,the microstructure evolution of metal copper and copper-zirconium alloy during high-pressure rapid solidification were studied,in term of energy-temperature curve,pair distribution function,and La SCA.The following conclusions were obtained.（1）The potential energy of liquid metal copper increases with pressure,but the randomness of non-equilibrium phase transition of rapid cooling causes the energy of solid copper to not change monotonically with pressure.The specific heat of liquid Cu is always greater than that of solid Cu at all pressures.There are pressure-and process-independent constants during rapid solidification:in supercooled liquid copper,there are the total of 33 types of topologically close-packed（TCP）atoms;at the temperature T_cat which the crystallization begins,the type of La SC of atoms,the average coordination number of atoms,and the number of TCP atoms are fixed at 3300,13.08and 18.3%.Based on TCP structures,the essential structural characteristics of the liquid metal can be revealed.（2）The copper-zirconium amorphous alloy Cu₅₀Zr₅₀ is obtained by rapid cooling at the pressure not higher than 15 GPa,where the onset temperature of amorphization increases with pressures and therefore the glass forming ability（GFA）is enhanced.The number of the short-range order structure S555 increases rapidly with pressure,and so does S666.Therefore,S666 is a factor that must be considered when discussing the amorphous structures.Not only is the TCP structure much higher than the icosahedron（ICO）in number,but it can reasonably explain the existence（or even increase）of S444 and S666 in metallic glasses,so the TCP structure can more effectively describe the structural characteristics of metallic glasses.