Development of fabrication technology cold spraying for innovative coating by means of collision of high velocity solid particles

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Cold spraying has developed as a new technology to perform a high quality coating due to its lower heating of the powder. Relatively soft metals have been effectively coated by the process and superior coating properties compared with conventional coatings thermally sprayed have been reported. To establish the high quality coating by the process, utilization of fine particle may be effective. Typical identity of the process compared to the ordinal thermal spray process can be given by the coating formation unit as a solid particle, which collided onto the substrate surface or prior deposited coating surface at a quite higher velocity. To attain such a high collision velocity of the particle, especially for the fine particle around few pm in diameter, optimization in nozzle design still has to be performed. On the other hand, in a practical cold spraying, it has been indicated that the nominal velocity of the particle differ from net collision velocity due to bow shock effect on the sub … More strate surface. To realize a high collision velocity of the particle actually, especially in fine particle, bow shock problem onto the substrate surface has to be overcoine.To improve the deposition efficiency of copper fine particles, around 5 pm in diameter, in cold spray process onto metallic substrate, optimization in nozzle design was performed by numerical simulation. Particles velocity reached up to 585 m/s under the optimum conditions by using self-designed nozzle based on the simulation results. In the spraying of copper particle onto normal steel substrate, unique lamellar-like microstructure was formed near the interface region in the steel substrate. Work hardening may be induced significantly due to the higher velocity of the particles attained. Moreover, to reduce the bow shock effect on the substrate surface region in cold spray process, special nozzle was newly designed. The deposition efficiency, Vickers hardness and coating adhesion strength increased significantly especially in the case of both fine particle and 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 nozzle newly designed. 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 by 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 with conventional one Less