Deposition of Copper Fine Particle by Cold Spray Process

To improve the deposition efficiency of copper fine particles mean diameter around 5 mu m onto metallic substrate surface in cold spray process, optimization in nozzle design was performed by numerical simulation. Particles velocity reached up to 585 m/s under the optimum conditions with originally designed nozzle based on the simulation results. In the spraying of copper particles onto normal steel substrate, lamellar-like microstructure was formed near the interface in the steel substrate. Correspondingly, remarkable hardness increase in this lamellar-like region of the steel substrate was recognized due to the higher velocity of the particles attained. Moreover, to reduce the bow shock effect especially for fine particles on the substrate surface in cold spray process, special nozzle was newly designed. The deposition efficiency, Vickers hardness and coating adhesion strength increased significantly especially in case of fine particles, as well as at higher pressure level of the working gas, while nominal particle velocity decreased with the special nozzle. Numerical simulation indicated that the pressure levels on the substrate surface decreased effectively in the newly designed special nozzle. In the observation of sprayed individual particles onto the substrate, extended metal jet was recognized at the splat's periphery when the particle was sprayed with the special nozzle. The results indicate that the decrease of particles velocity due to bow shock was suppressed effectively in the special nozzle as compared to the conventional one. [doi:10.2320/matertrans.MRA2008223]