Cold gas spraying is a coating process by which coatings can be produced without significant heating of the sprayed powder. In contrast to the well-established thermal spray processes such as flame, arc and plasma spraying, in cold spraying there is no melting of particles prior to impact on the substrate. Bonding occurs when the impact velocities of the particle exceed a critical value. This critical velocity depends not only on the type of the spray material, but also on the powder quality, the particle size and the particle impact temperature. The present contribution summarizes general views and reports recent developments with respect to the understanding of the process and respective consequences for the optimization of the process. The presented optimization procedure covers principles to increase gas and particle velocities and rules to decrease the critical velocity for bonding. By consequently following such route for typical metallic spray materials, cold spraying as a quite new coating technique is already capable to provide coating qualities very similar to those of work hardened bulk material at powder feed rates similar to those of thermal spraying and deposition efficiencies of about 90 %.

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