The cold gas dynamic spraying process solves many issues with respect to the deposition and additive manufacturing of metals. Namely, it provides a reduced reactive environment, simplicity of operation, and high deposition rates. It is known that the deposition efficiency of the cold spray process can be substantially increased using helium instead of nitrogen as the process gas. However, the use of pure helium can be cost prohibitive in many situations and commercially available helium recovery systems constitute a major capital investment on top of the spray system and ancillary equipment. This work focuses on the development and use of a novel, inline gas mixing system, designed to provide a blend of nitrogen and helium at any ratio. Deposits produced with different gas ratios were investigated through particle velocity, deposition efficiency, porosity, and hardness. The experimental results show that helium, even in lower percentages, can have a significant effect on deposition efficiency and that helium percentage can be optimized to reduce the overall coating production costs. From the results, a cost model is presented which, when provided experimental values and user costs, can be used to identify the nitrogen-helium ratio that will produce the lowest overall coating cost.

This paper describes the influence of post-spray heat treatment parameters on mechanical properties of Ni-TiC composite coatings. Thin Ni-TiC composite coatings were produced by low pressure cold gas dynamic process (also referred as cold spray or kinetic spray process) on an Inconel alloy substrate. In the coating process, mechanically mixed micron-sized Ni-TiC powders (~50 µm) were injected into a de-Laval nozzle propelled by a supersonic gas stream to high velocity (>300 m/s) to impinge upon a substrate. The coatings are formed subsequently as the metallic particles are severely deformed plastically and bonded to both the substrate and to one another. However the tensile adhesion strength levels were determined to be in the range of 10-14 MPa. A subsequent post-spray heat treatment in vacuum was found to enhance the bond strength of the coated particles with the substrate due to good metallurgical bonding caused by diffusion mechanism.

The present study was carried out to evaluate the applicability of the Gas Dynamic Spraying (GDS) of different powder compositions for depositing wear-resistant composite coatings on iron and steel castings. This process, simply known as “cold spray,” utilizes the kinetic energy of particles sprayed at supersonic velocities to produce a bonding of the particles to the substrate. Ni and Cu based coatings containing W, Zn and TiC as reinforcement were made by the low pressure GDS technique and investigated. The coatings microstructures were studied by both optical and scanning electron microscopy. Phase composition, hardness and wear resistance of the GDS coatings were analyzed. The ball-on-disc sliding wear test was used for assessing the wear resistance characteristics of the coatings using a ceramic (Si 3 N 4 ) ball. W and TiC reinforced coatings showed the best wear performance. These were further evaluated in greater detail. In addition to the obtained test results, the application prospects for such GDS coatings were discussed.

A computational fluid dynamic (CFD) model of the cold gas dynamic spray process is presented. The gas dynamic flow field and particle trajectories within an oval shaped supersonic nozzle as well as in the immediate surroundings of the nozzle exit, before and after the impact with the target plane, are simulated. Predicted nozzle wall pressure values compare well with experiment. In addition, predicted particle velocity results at the nozzle exit are in qualitative agreement with those obtained using a side-scatter laser Doppler anemometer (LDA.) Details of the pattern of particle release into the surroundings are visualized in a convenient manner.