The modeling of the cold gas dynamics spray process is conducted. The Navier-Stokes equations are solved for the gas flow, including turbulence model equations. The model is validated with experimental measurements for flows with and without shock waves. It predicts accurately the gas flow for both cases. A one-dimensional model is used to track the particles injected in the flow. It is shown that the effects of the shock wave present in front of the substrate are not negligible for small diameter particles and have a direct influence on their impact velocity. The spray stand-off distance is shown to have a direct effect on the flow structure and on the impact velocity of the particles. It is shown that the one-dimensional approach is not sufficient for the particle analysis.

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.

Supersonic, two-phase flow of a gas/particle mixture directed towards a substrate may enable the deposition of "cold" particles onto a "cold" substrate under certain conditions. The method is commonly known as Cold Gas Dynamic Deposition or Cold Spray. Current research shows that copper can be deposited within a wide range of parameters and velocity regimes, whereas the deposition of other materials may involve difficulties depending on the material properties and substrate characteristics. Although particle velocity is recognized as being the key factor in the deposition of particles with the cold spray process, it alone cannot describe the state of the particle prior to and during impact. A simple analysis shows that the impulse of particles with equal particle velocity and size depends significantly on its density. For common engineering metals, an interval varying by up to a factor of 5 is possible considering, for example, magnesium and molybdenum. The impact force, directly dependent on the particle's impulse, governs the pressures generated during impact. In a simplified calculation, pressure values of around 3000 MPa can be very easily determined. While the particle impulse accounts for the degree of interaction - partial or complete deformation - the particle's and the substrate's lattice structure and its capacity to deform determine the type of particle substrate interaction. Depending on these properties, the substrate, the particle or both will be deformed. Evaluating impact experiments shows distinct differences between the impacts of copper, steel and aluminum particles on aluminum and steel substrates. The paper presented may be seen as a contribution to the discussion of a theory to evaluate coating and substrate combinations prior to spraying in order to predict bonding and coating build-up or to offer guidance concerning the optimum parameter set for deposition.

The interaction of the supersonic gas jets of rectangular section with a flat obstacle under conditions of the Cold Spray process was studied. Pressure distribution on the obstacle surface at various jet regimes is measured. Instability of the jet as well as compressed layer structure is observed with the aid of laser Schlieren visualization. Depending on jet pressure ratio, distance between nozzle exit and the obstacle various modes of the jet are registered including classical mode, the mode with peripheral maximum and circulate bands, the mode with oscillations of bow shock, and the mode with jet oscillations. It is shown that the distribution of pressure along the smaller size of the nozzle is self-similar in the classic regime of the impingement and does not depend on the angle of encounting at φ= 50 - 90°. The critical parameters of the gas, when it accelerates along the surface, are reached near the boundary of the falling jet. The distributions of the stagnation temperature and heat transfer coefficient in the near-wall jet at various stand-off distances are experimentally obtained. It is shown that the experimental data on the heat transfer coefficient are higher than the calculated ones, and this difference can be explained by velocity fluctuations in the vicinity of the stagnation point and in the near wall jet.

Electroplated nickel can be used to fabricate miniature components such as gears, linkages, and other two-dimensional mechanical structures. This process produces excellent parts, but it is slow and somewhat expensive. Because cold spray produces low oxide-content, high-density deposits at a high rate, cold spray processing might be a viable alternative to electroplated nickel components. In addition, cold gas-dynamic spray can process materials, such as stainless steel and aluminum, which can not be electroplated. The purpose of this study was to evaluate the mechanical properties of cold spray nickel in the as-sprayed and heat treated conditions, then compare them to those of bulk nickel and electroplated nickel. Characterization of freestanding structures is subjective since the final product of any thermal spray process produces a material unlike any other material formed by conventional techniques. Specifically, this investigation determines the mechanical characteristics of nickel, through metallographic imaging and tension testing. Metallographic imaging showed that as-sprayed nickel has slightly more voids than the heat-treated structures. Tension tests of the as-sprayed nickel showed little plastic behavior, while a heat treatment gives much more ductility without compromising ultimate strength.

In wire arc spray, atomizing gas is one of the most important parameters. The atomizing gas in wire arc spray is improved by using super sonic cold gas (non combustion gas) jet for better coating characteristics. To generate the super sonic cold gas jet, one is an optimization of nozzle shape with conventional compressed gas and another is that the pressed gas heated at 500-800K is supply to converging-diverging nozzle. Namely, coating deposition mechanism of cold spray, which is high particle impact velocity to substrate, is applied to wire arc spray. In this study, gas dynamics investigated the effect of pressure and temperature of supplied nitrogen gas, nozzle geometry on wire arc spray process (thermodynamical behavior of atomizing gas and coating properties).