In cold spraying, in contrast to thermal spraying the coating material is not melted prior to the impingement onto a substrate. The powder particles are accelerated to high velocities by a supersonic gas jet. Even though the particles are in a solid state, they form a dense and solid bonded coating upon impact. In order to form a dense coating with sufficient adhesion to the substrate, the particles have to reach a certain velocity before hitting the substrate. This velocity is characteristic of the coating material and also depends on the particle temperature. A variety of experiments have been carried out with copper as spay material in order to determine the critical velocity for solid bonding of particles onto the substrate. To investigate the effect of spray parameters and nozzle geometry on the velocity and temperature of the particles, computational fluid dynamics was performed. The calculations allow a direct correlation between experimentally obtained deposition efficiencies and process parameters. Finite element modeling of the particle impact could relate successful bonding to high strain rate phenomena at the particle interface. In view of the above criteria an optimization strategy for cold spray process can be developed.

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