An analysis of the cold spray process and its coatings

In this study, computational fluid dynamics (CFD) and extensive spray tests were performed for detailed analyses of the cold spray process. The modeling of the gas and particle flow field for different nozzle geometries and process parameters in correlation with the results of the experiments reveal that adhesion only occurs when the powder particles exceed a critical impact velocity that is specific to the spray material. For spherical copper powder with low oxygen content, the critical velocity was determined to be about 570 m/s. With nitrogen as the process gas and particle grain sizes from 5-25 mum, deposition efficiencies of more than 70% were achieved. The cold sprayed coatings show negligible porosity and oxygen contents comparable to the initial powder feedstock. Therefore, properties such as the electrical conductivity at room temperature correspond to those of the bulk material. The methods presented here can also be applied to develop strategies for cold spraying of other materials such as zinc, stainless steel, or nickel-based super-alloys.