Development and application of the low critical velocity cold spray process

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The Low Pressure Cold Spray (LPCS) technology has proven its capability of in-situ material build-up from tens of microns to centimeters, varying the composition and characteristics of the formed coatings, and imparting to the deposited coatings such properties as high density, high conductivity and/or corrosion resistance. However, the low deposition rate is one of the main unresolved short comings of the LPCS process, substantially limiting its industrial usage. The low deposition rate is correlated with particle velocity, which is necessary for forming of dense coating. It has been well established that impacting particles must exceed a critical value of particle velocity, called - critical velocity, to deposit on instead of bouncing off the substrate. The magnitude of the critical velocity generally depends on several factors, including particle and substrate material properties, particle temperature and size, particle and substrate surface conditions, etc. Of special interest is the presence of an oxide layer on the particle surface and its ability to considerably affect the critical velocity. Developing a method to manage the critical velocity of the feedstock powder material is very important, because the lower the critical velocity, the higher the deposition rate of the accelerated powder particles. The project offers to resolve the low deposition rate problem by controllably decreasing the particle oxide film thickness, using plasma pre-treatment of feedstock metal powders. The overall objectives of the project are: (a) developing a Low Critical Velocity Spray process (LCVS) by using plasma pre-treated Al and Cu based feedstock powder compositions intended for EnWin Utilities, Ltd., applications and (b) implementing the developed LCVS process into a compact proof of concept prototype LPCS system, with an elevated deposition efficiency.