Cold spray modeling and validation using an optical diagnostic method

Abstract

The Cold Gas Dynamic Spray process uses the kinetic energy of unmelted sprayed particles to produce coatings. The most important element of the cold spray system is the nozzle used to accelerate the particles. Consequently, the nozzle design optimisation is a key to improve the coating quality and reduce the spraying costs. In this study, an axi-symmetric two-dimensional mathematical model is presented and used to predict the flow inside a cold spray nozzle as well as the particle velocity in the vicinity of the nozzle exit. The model results are compared with those obtained using the one-dimensional isentropic theory and with particle velocity measurements made on a commercial cold spray system. The study shows that the particle exit velocity depends on the type, stagnation temperature, and pressure of the propellant gas. The comparisons show that the proposed model is more accurate than the one-dimensional theory. It allows predicting accurately the behavior of the particles in the cold spray jet even in the presence of shock waves. Following this work, the design of new nozzles for specific applications using this mathematical model can be considered.