This study investigates the use of cold gas spraying (CGS) for depositing braze filler coatings. In the experiments, pure Cu layers were sprayed onto Mg alloy substrates, which were then joined to AlSi steel by contact reaction brazing in a vacuum furnace. The bonding temperature influenced the dissolution of Cu as well as the eutectic reaction between the coating and substrate. The thickness of the brazed seam was found to be 300 μm although the initial thickness of the Cu layer was just 50 μm. The shear strength of the joint peaked at 37 MPa, corresponding to a brazing temperature of 530 °C. Intermetallic phases and interfacial defects of various types were responsible for the low strength of the joints.

Solid oxide fuel cells (SOFCs) are one of the options as auxiliary power units (APU) in transportation, e.g. in vehicles or in aircraft. In particular, metal supported SOFCs consisting of metallic frames and substrates coated with plasma sprayed functional layers have shown an excellent stability concerning redox cycling. In order to provide sufficient power, these single cells have to be assembled to stacks. To prevent short-circuiting the frame of each cell has to be electrically insulated from the neighbouring one. For that purpose a ceramic coating is applied on each metal frame by thermal spraying before it is brazed to other stack components. Such layers should at one hand show good wetting and adhesion to the silver based brazing materials. On the other hand it should maintain sufficient electrical resistance even at the fuel cell operating temperature. As the applied solder, which connects the cells and seals the gas manifold simultaneously, is an excellent electrical conductor, it is mandatory to prevent the brazing material from penetrating into the deposit. In this paper a description of the design and experiences with these plasma sprayed insulating layers is given.

The conventional manufacturing process of the automotive brazed heat exchanger includes complex preparation processes before brazing: aluminum brazing filler alloy is pre-claded on both sides of a fin by an extrusion method, and holed aluminum tubes are coated on both sides with Zn for corrosion protection by a wire arc spraying process. The intent of this study is to simplify the preparation process by kinetic spraying using all of the components, including Al-12%Si (for the brazing filler metal), Zn (for corrosion protection), and KAlF4 (flux powder). Four kinds of blended powder, with and without flux, were evaluated. The bond properties and composition distribution at the braze joint area were evaluated by SEM and an electron probe micro analyzer (EPMA). It was necessary to control the Zn content so that the corrosion resistance and brazeability of the aluminum heat exchanger would not be affected. An optimal kinetic spray condition was obtained, in order to fabricate the heat exchanger in this study. It was observed that the joints of the brazed specimens on each side of the brazing part were sounder than those achieved brazed by the conventional methods. Further, the kinetic sprayed heat exchanger showed acceptable corrosion protection.

Application of cold gas spraying for deposition of braze filler coatings is investigated. Different light weight alloy substrates, i.e. aluminum AA1050, AA3005, AA5754 and AA7022, magnesium AZ91 and titanium TiAl6V4, are used. Filler coating materials depend on the substrate melting temperature. So for aluminum alloys Al12Si and zinc based fillers, for AZ91 pure zinc and for Ti6Al4V different Cu-Ni blends are applied. CGS process parameters are varied with regard to process gas (nitrogen) temperature and pressure, powder feed rate and spray distance. Correlation to process characteristics and economical aspects are given. The usability of the produced filler coatings is shown by different optimized brazing/soldering processes. In case of aluminum braze joints a full metallographical investigation is carried out by optical and scanning electron microscopy as well as EDXS analyses. The gathered results are compared with those of conventional filler material addition, i.e. wire, roll plating and foil.

The use of modern thermal spraying techniques for filler metal application may offer new solutions for brazing complex metal components without fluxing agents, when the spraying processes are fitted to the requirements of the following brazing process. The necessary coating parameters always depend on the kind of base material, the geometry of the joint, the used filler metal, and the chosen heating process for brazing (heating in vacuum or protective atmosphere furnaces, inductive or flame heating etc.). Copper and nickel based alloys are typical filler metals for brazing complex components made of stainless steel (heat exchanger, fuel pipe systems, exhaust systems, catalytic devices etc.). Using these examples, the results of brazing experiments and technical aspects of thermally sprayed braze coatings compared with conventional filler metal application techniques are discussed.

Both bonding strength of coating to substrate in low pressure plasma spraying and the effect of reverse transferred arc treating before spraying are studied in this paper. It is difficult to obtain the bonding strength precisely in low pressure plasma spraying by standard testing methods, such as, ASTM Standard C633-79 and JIS H8666-80. Therefore, for the bonding strength test rather than using a conventional adhesive, we believe a vacuum brazing process using Ag-Cu-In-Ti active filler metal at 1023 K should be used. We have also confirmed the practicality of this step. By the above test method, it has been proven that the bonding strength of low pressure plasma sprayed coating is over 100 MPa. Also, that reverse transferred arc treating after blasting enhances the bonding strength of low pressure plasma sprayed coating. It is also believed that the projections formed on the substrate surface by reverse transferred arc treating are buried into the coating and perform the pile effect.