Effect of injection pressure on particle acceleration, dispersion and deposition in cold spray

The effect of injection gas pressure on particle acceleration, dispersion and deposition in cold spray process was investigated by both numerical and experimental methods. A computational fluid dynamics (CFD) model was developed which exactly matches the real nozzle in experiment to predict the supersonic gas flow field and particle velocity prior to the impact. Based on the simulation results, it is found that injection pressure significantly affects the flow field of the driving gas. Higher injection pressure leads to higher injection flow rate as well as powder injection rate, producing thicker coating on the substrate. Besides, the particle footprints on the substrate surface at different injection pressures were predicted and compared with the experimental measurements of the single track coating width. The results indicate that particles disperse more widely at higher injection pressure. In addition, the parameter η which refers to the ratio of particle impact velocity to critical velocity is used to evaluate the effect of injection pressure on coating characteristics. With increasing the injection pressure, both η and deposition range have a downward trend, which implies the deterioration of the deposition efficiency and coating bonding strength. For the purpose of validation, the deposition efficiency of copper coatings was also experimentally measured at different injection pressures, which confirms the numerical analysis.