Optimal design of a cold spray nozzle by numerical analysis of particle velocity and experimental validation with 316L stainless steel powder

The optimization of exit diameter of a cold spray nozzle under different spray conditions was investigated numerically for the first time. The optimal expansion ratio is influenced by the gas conditions, particle size, nozzle divergent section length and throat diameter. The optimal expansion ratio increases with the increases in gas pressure and nozzle divergent length. It decreases with the increases in gas temperature, particle size and nozzle throat diameter. The optimal expansion ratio using He is less than that using N2 under the same operating conditions. The experiment with a 316L stainless steel powder indicates that a dense 316L stainless steel coating with a high microhardness can be deposited with an optimized nozzle using air as an accelerating gas owing to the high particle velocity. The good correlation of particle velocity with the coating microstructure and microhardness confirmed the optimal design method.