Effect of Heat Input to the Substrate on Coating Properties during Cold Spraying

Previous work showed that, depending on the cold spray system and nozzle configuration, the substrate surface temperature can rise up to a value close to the inlet gas stagnation temperature in the area located beneath the cold spray gun where the sprayed particles are deposited. In typical spray conditions, the inlet gas temperature ranges from room temperature to up to 800°C. The heat input could therefore be high enough to soften the surface on which the particles are deposited. As a consequence, the adhesion conditions change significantly with the increasing inlet gas temperature. Moreover, the increase in surface temperature may also influence the coating build-up itself after depositing the first layer and so modify the coating properties.

The influence of the heat input to the substrate beneath the cold spray gun on coating properties and build-up characteristics during cold spraying of copper powders is investigated. The spray parameters have been chosen in order to show similar particle velocities (measured by optical diagnostics) while leading to different substrate and coating surface temperatures (measured by ultrafast infrared imaging). The effects of surface temperature on oxygen intake, deposition efficiency, electrical resistivity, porosity, micro-hardness and other microstructural features are analysed and discussed.