Research On The Structure And Kinetic Properties Of Metal Solid-liquid Interface

The properties of the solid-liquid interface is known to be fundamental important in understanding many phenomena and processes in material sciences, such as the crystal nucleation within melt, the near-equilibrium crystal growth, the interfacial solute segregation and the wetting of liquid droplets on solid substrates, etc. Due to the difficulties in performing direct measurements on solid-liquid interfaces, computer simulations, have become a good way in evaluating the interface properties. The molecular dynamics (MD) simulations have been performed to explore the structure and kinetic properties of liquid-solid interface of pure metals and alloys based on a potential of embedded atom type, named by Zhou. The main contents and results are as follows:We presented MD simulations on the structural order of solid-liquid interface of Co. The number density profiles and ordering parameter profiles of solid-liquid interface for the (100),(110) and (111) interfacial orientations have been calculated. The number density profiles show that there are some ordering structures in the liquid region approaching the solid-liquid interface. The values of number density change faster than those of ordering parameter at the interface. The calculated values of two dimension pair correlation functions for the (100) interfacial orientation differ at the different interface layers, indicating that the transition from crystal to fluid occurs over a region of only6layers.The kinetic properties of liquid-solid interface of Co have been studied. By determining the time dependence of the volume per particle for different temperatures, the simulated melting temperature of1720K, is a little lower than the experimental one of1770K. The calculated kinetic growth coefficient agrees well with the latest experimental result. The anisotropy of kinetic growth coefficient is given by μ100>μ110>μ111, which is consistent with other metals. The relationship of interfacial velocity and temperature has been investigated at temperatures ranging from1720K to OK. The movement of solid-liquid interface can be described by diffusion limited (W-F) model at higher temperatures; while at lower temperature, it can be fit by a simple Arrhenius type expression. The calculated diffusion activation energy is almost close to zero under high undercoolings, although the crystal growth still proceeds with the speed of about60m/s, indicating that the movement of interface is not controlled by diffusion mechanism under deep undercoolings.Molecular dynamics simulations have been performed to explore kinetic properties of liquid Cu50Ni50alloy. When the volume remains the same, the simulated melting temperature of Cu50Ni50alloy is determined, which is a little lower than the experimental one. The calculated interface velocity increases with the increasing undercoolings ranging from0K to335K, where the calculated values are a little higher than the experimental ones at higher temperatures, and in agreement with the experimental ones at lower temperatures. What’s more, the relationship of interface velocity and temperature has been investigated to make comparison to the results of Co in the last chapter. Cu50Ni50alloy shows the same tendency with Co at the whole temperature regions. We also fit the data by a simple Arrhenius type expression at lower temperature. The activation energy of atom is almost close to zero under deep undercoolings, although the crystal growth still proceeds with the speed ranging from50m/s to10m/s, indicating an athermal process.