The influence of nozzle design in the cold spray process

Abstract

Publisher Summary One of the major characteristics of the cold spray process is the high-speed gas jet, which is governed by gas dynamics. In gas dynamics, supersonic flows are obtained with Convergent-Divergent [“CD”] nozzles (or de Laval nozzle), which are used for rocket motors. While the principal purpose of the design of a rocket motor nozzle is to maximize the thrust, in thermal spraying, the main purpose is to obtain better coating quality. The studies on thermal spraying show that the coating properties are principally determined by the thermal and kinetic energy states of particles upon impact with the substrate. To have a balance between these two states, various changes in the design of the High-Velocity Oxygen Fuel [“HVOF”] gun nozzle have been attempted. However, works concerning the influence of nozzle geometry on the thermal spray process are sparse. The effects of throat diameter and exit divergence of the gun nozzle on the HVOF process have been considered. The combustion gas flow (such as pressure, velocity, temperature and expansion state of gas jet from the nozzle exit), the particle behavior and, therefore, the nature of coatings were found to be significantly influenced by these nozzle parameters. In addition, the effect of the expansion state of the combustion gas jet on the HVOF process was investigated using a diverging nozzle exit.