Development of ejector nozzle for high-pressure cold spray application: a case study on copper coatings

For coating deposition and additive manufacturing by cold spray, supersonic de Laval nozzles are traditionally used. The application of other configurations of the prechamber-nozzle units allows for the expansion of the technological capabilities of cold spray. In particular, the use of an ejector nozzle allows utilizing an open-type powder feeder, which does not require maintaining high pressure inside itself. In the present paper, for the first time, the possibility of application of the ejector nozzle under high-pressure cold spray conditions was investigated. A comparative analysis of the main characteristics of copper coatings deposited on aluminum alloy substrates using both the ejector and de Laval nozzles was also performed. It was demonstrated that the coatings obtained using the ejector nozzle are characterized by lower thickness, higher porosity, and similar microhardness as compared to the coatings obtained using de Laval nozzle. This development can be in demand in cases where the use of an open-type powder feeder is necessary to ensure technological simplicity of the cold spraying process.