Open pore metallic foam core sandwich structures prepared by thermal spraying of a coating on the foams can be used as high efficiency heat exchangers due to their high surface area to volume ratio and consequent high heat conductivity. The quality of such skins which is indicated by coating porosity, oxide content, adhesion and mechanical strength plays a significant role in applicability and efficiency of the heat exchangers. In this research a twin wire arc thermal spray process optimized to deposit a dense and high strength Inconel 625 skin on 40 pores per linear inch (PPI) nickel foam sheets. The effects of grit blasting parameters on the surface characteristics of substrate (paste filled foam) were investigated through a DOE method. In-flight characteristics of the molten droplets and their effects on the coating properties were investigated by DPV-2000 monitoring system for three different spraying distances. Characterization of the prepared surface and sprayed skin were conducted using SEM, EDS, roughness measurements and adhesion test. Based on statistical analysis and experimental investigations of the coating, a small range of grit blasting parameters were indicated as surface preparation criteria to get an acceptable adhesion of the skin to the foam with the minimum amount of porosity and oxide in the coating. Effects of the different wire arc spraying distances were also studied and optimum distance was specified to fabricate foam core sandwich structures.
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