The Research On Gas-Solid Two-Phase Flow Shock Wave And Deposition Behavior On Metal Surface Molecular Dynamics Simulation In Cold Gas Spray

Supersonic cold gas spray is a new coating process which has many good attributes and it has attracted attentions from scholars in and abroad. But as a newly-developed technology, it is short of perfect theory and the quality and the efficiency of spray should be improved. And what's more, it has not been carried out in practical project although it can be applied to nanometer-sized particle spray. In order to illustrate the mechanism of supersonic gas-solid two-phase flow and the deposition behavior on metal surface in cold gas spray, this paper has done the following researches: gas-solid two-phase sound velocity and shock wave,Molecular Dynamics Simulation of the melting point of nanometer-sized Au,Molecular Dynamics Simulation of the deposition behavior of nanometer-sized Au clusters on a Au surface.First, considering the balance of the two-phase mixture, we derive the sound velocity of gas-solid two-phase flow from Laplace's Equation of isentropical sound velocity and analyze the sound velocity of different gas-solid two-phase mixture. The experimental results show that pressure and volume ratio of gas has much influence on sound velocity. This conclusion is consistent with Prandtl's analysis and agrees well with the experimental results. Second, we present a two-phase shock wave model based on two-phase sound velocity which is more suitable for the two-phase shock wave than single- phase sound velocity model and analyze the effects to shock wave by phase slip, heat transfer between phases, different materials and parameters upstream shock. The results show phase slip, pressure upstream shock have a little effects on shock wave, but Mach number, velocity, sound velocity and gas volume ratio upstream shock are the main working factors.Using many-body potential function, we simulate nanometer-sized Au clusters which have atoms ranging from 256 to 32000 by Molecular Dynamics Simulation and then analyze the melting point change with the change of size of clusters by calculating the radial distribution function. We can see that the melting point decrease along with the decreasing of the size of clusters. when the atoms is below 5000, the melting point we calculate is same as the ones calculated before and the melting point of the nanometer-sized clusters can be calculated by the radial distribution function with precision. When the number of atoms is above 5000, the melting point we calculate is higher than ones calculated before. When the number of atoms is above 9000, the...