High Rate Deposition in Cold Spray

As cold spray applications are industrialized, conservation of the process materials and the cost effectiveness of the cold spray procedures become significant. Intelligent design of the cold spray process parameters can provide great service in this regard. Especially the mass flow ratio of the powder to the process gas in the nozzle. Prior studies have shown that, aerodynamically, the powder to gas mass flow ratio can be increased to much higher than traditionally adopted without much change to the particle impact velocities and temperatures. However, at high powder feeding rates attention needs to be paid to the control of the deposition to avoid local over-deposition and to keep the microstructural coating quality. In this work, high rate deposition of tantalum was studied by producing coating specimens by varying the powder to helium mass flow rate from 5% to 15%. Quasi-1D fluid simulations yielded a minimal effect of increased powder stream loading on particle impact velocity and temperature. Furthermore, the experimental specimens were examined through micrographs, porosity measurements, and hardness tests to show practically the same structures. The increased stream loading rate however helped increase the cost efficiency and gas efficiency of the operation by 300%.