Numerical Analysis Of Gas-particle Two Phase Flow In Vacuum Cold Spraying

The particle impact velocity is a key factor affecting the particle deposition in thecold spray process. It is difficult for submicron particles to realize effective deposits ortheir deposition efficiency is very low in the traditional cold spray with atmosphericenvironment when the submicron particles are subjected to the bow shock before thesubstrate. So the influencing factors on the submicron particles impact velocity werediscussed in the vacuum environment combing with the principle of the traditional coldspray and accelerating behavior of the submicron particles in the high-speed air flow.The research includes:Effects of standoff distance, particle diameter and density on particle impactvelocity in the atmospheric environment were studied by numerical analysis method.The results showed that the Cu particle best size range was0.8-15μm provided that thecarrier gas was air, inlet pressure P0was33.67atm, inlet temperature T0was600K, andstandoff distance SoD was25mm based on the critical deposition velocity was500m/s.The main parameters of effects of ambient pressure, or chamber pressure Pamb,standoff distance and temperature on submicron particle impact velocity in the vacuumenvironment were studied. The results showed that ambient pressure was the key factorsaffecting the submicron particle impact velocity. The submicron particle impact velocitygradually increased with the conditions of P0=5atm, T0=600K, SoD=25mm when theambient pressure decreased from1atm to0.1atm. The impact velocity of submicronparticles increased a little when reducing ambient pressure further. The impact velocitiesof Cu particles with the diameters of0.2-1μm in vacuum environment were much largerthan that under the atmospheric environment when the simulation conditions in vacuumcold spray were P0=5atm, T0=600K, Pamb=0.1atm, SoD=25mm, and in traditional coldspray of P0=33.67atm, T0=600K, Pamb=1atm, SoD=25mm. The submicron particleimpact velocity increased with the increment of the inlet temperature. The best size ofCu particle were0.4-5μm in vacuum environment with the conditions of P0=5atm,T0=600K, Pamb=0.1atm, SoD=25mm.The heat transfer process between the gas and the nozzle wall in the vacuumenvironment was studied considering the nozzle wall, the nozzle wall temperature distribution, and the changes of particle impact velocity under the nozzle of differentmaterials were also analyzed. The results showed that the nozzle temperature wasreduced gradually from inside to outside and the temperature of the nozzle throat wasthe highest; the lower thermal conductivity of the nozzle material, the higher thesubmicron particle impact velocity.The research may provide theoretical instruction for the preparation of submicroncoating.