Simulation of Cold Spray Nozzle Accompanying a Water-cooling Adjustment

Cold spraying is a coating process which enables production of metallic and metallic ceramic coatings with dense (very low porosity level) and pure (low oxygen content) structures. Several coating applications such as corrosion resistance and electrical conductivity rely on these properties. Generally, cold spraying is based on higher particle velocities and lower process temperatures than other thermal spray processes. The coating is formed in a solid state when feedstock particles impact on a substrate with high kinetic energy, deform and adhere to the substrate or the previous deposits. Therefore a high pressure gas is usually necessary to accelerate the particles to a sufficient kinetic energy terms of velocity to obtain an intensive plastic deformation. Also, quality of the coating depends on particle size distribution and shape, gas pressure, gas temperature, gas molecular weight, nozzle shape and so on. In commercial cold spray applications where the cost efficiency is mostly considered, continuous flow of work is required. However during the deposition, the nozzle of a cold spray system operating high pressure and temperature will foul with the metallic powder causing system failure and rework removing damaged nozzle. To solve that problem number of nozzle assemblies are introduced accommodating venturi adjustments or adoption of synthetic fiber (PBI) instead of typical nozzle materials including brass, stainless steel or tool steel. In our experience based on commercial practices, a water-cooling nozzle assembly will also help to achieve to provide continuous deposition without clogging. In this work we focus on a water-cooling convergent-divergent nozzle design and its effects on particle velocity which is the most important parameter in cold spray practice. A computational fluid dynamic (CFD) model of the cold gas dynamic spray process is presented. The gas dynamic flow fields within both typical adiabatic and water cooled de-Laval nozzles as well as in the immediate surroundings of the nozzle exits is simulated. Predicted particle velocity results at the nozzle exit are compared with experimental data which are obtained using a commercially available in-flight particle condition monitoring system. In addition details of predicted nozzle wall temperature values and particle velocities are visualized in a graphical manner.