This paper represents an effort to systematize an understanding of the cold spray process and the suitability of material for such a process. The evaluation is based on a brief analysis of the powder particle impact and a literature research concerning shock compression phenomena in matter and related physical effects, such as impact heating and dynamic yielding. The FEM simulations performed permit estimating the maximum impact pressures, the deformation rates and the deformation kinetics during impact. The calculations can be verified experimentally and are supported by the data published. From a brief analysis of the equations of state applied to shock compression, key material parameters are derived and investigated. A parameterization of physical properties and correlation with the crystal types endeavors to provide a ranking of material suitability.

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.

Atmospheric Rheo-Spraying (ARS) using the HVOF process enables injection-molded structures and thick-film coatings from steels and from high-temperature Ni-based alloys with layer thicknesses down to the centimeter. The ARS process control is based on the thermal spraying of particles in the solid state at a maximum average speed of more than 600 m/s. The coating consolidation to porosity values below 1% occurs through the particle impact with high kinetic energy. Because of the low particle oxidation, the mechanical properties of the heat-treated injection-molded structures are comparable to those of forged alloys. In this paper, ARS injection molding is successfully implemented in combination with an innovative manufacturing technique in rocket engine technology to produce a model composite combustion chamber with a thermally sprayed internal pressure jacket. Paper includes a German-language abstract.

In this paper, a coating system for a thermal barrier, consisting of a CoNiCrAlY adhesive layer (HVOF) and a zirconium dioxide top layer (APS), is optimized with the help of particle diagnostics. The paper describes the optimization approach for a thermal barrier coating system with the aid of particle diagnostics and considering the results of the hot tests carried out within the scope of TEKAN on the DLR technology test stand P8 in Lampoldshausen. The objective is to engineer a thermal protective coating in a duplex setup for a cryogenic rocket engine and its heat flow densities of approximately 80-90 MW/meter square. Paper includes a German-language abstract.

New near-net-shape structures of alloy Inconel 718 processed by HVOF spraying require optimum mechanical properties. Dominant factors defining the material quality are the particle properties velocity and temperature adjusted by the HVOF process parameters. Based on theoretical analysis of the HVOF process, experiments were performed with a defined variation of primary process parameters, producing coating samples of alloy 718 and measuring the particle velocities. Microstructural and X-ray analysis shows that in coatings with a high fraction of molten phase and high velocity, mainly divalent and spinell-type oxides are formed during particle impact on the substrate. Due to severe oxidation of the y'/y''- forming elements Ti, Al and Nb, precipitation-hardening effects of In 718 coatings are low. This leads to merely mediocre mechanical properties. The reduction of the molten phase to nearly zero leads to a drastic decrease of the oxide formation. The hardening γ'/γ'' phases are precipitated homogeneously in the Ni-base matrix. Strength values comparable to cast and wrought alloy In718 are attained by spraying with a low molten-phase fraction and high particle velocity. However, extensive intergranular 8-phase precipitation due to too high an Nb content of the powder causes only mediocre fracture elongation. Coatings up to 10 mm thick have been sprayed. The construction effort and hence the costs and weight of combustion chambers for hypersonic propulsion systems are to be reduced through direct thermal spraying of the loadbearing metallic pressure jacket onto the tubular cooling system. As a semifinished product, the selected Inconel 718 alloy exhibits good mechanical properties in the cryogenic temperature range as well as under higher thermal loads, and is commercially available in powder form. Aging serves to increase the strength up to the range of 1,200 N/mm2. For the sprayed In718 version, coating thicknesses in the centimeter range, a porosity < 1% and mechanical properties comparable with those of the cast version are required. The objective of the research work is to optimize spray-process control so that the resultant structural thick layers meet the design as well as the material requirements with respect to combustion-chamber technology. This necessitates elaborating the dominant microstructural parameters influencing the mechanical properties and the effect on them of the spraying process, and correlating them with the particle-condition parameters and the process parameters [1].