In this study, porous and dense layers of alloy 625 are deposited on nickel foam sheets using a modified twin wire arc spraying process. Sandwich panels with arc-sprayed alloy 625 skins on nickel foam cores were fabricated then subjected to four-point bend testing. The effects of skin porosity on flexural rigidity and overall mechanical behavior are investigated. The ductility of porous alloy 625 skins was improved after heat treatment at 1100 °C for 3 h.

In this study, twin wire arc spraying is used to deposit dense Inconel skins on 40 PPI nickel foam sheets. A design-of-experiments approach is used to investigate the effects of grit blasting on the surface characteristics of paste-filled foam. In-flight behavior of molten droplets and its effect on coating properties is assessed at three spray distances. The Inconel coatings are evaluated based on SEM and EDS analysis, roughness measurements, and adhesion testing. The results indicate that acceptable adhesion, porosity, and oxide content can be achieved over a small range of grit blasting parameters.

Recently, an advanced technique was developed to fabricate sandwich structures for high temperature applications by depositing alloy 625 skins on Ni alloy foam core by thermal spraying. This study tries to utilize an analytical model to estimate the mechanical performance of these structures based on the mechanical properties of the constituents. The mechanical behavior of the Ni alloy foam is assessed via compression testing, while tensile tests are used in the case of the alloy coating. The flexural rigidity of the sandwich structure is calculated using analytical models and experimentally obtained elastic moduli of the alloy 625 coating and Ni alloy foam. The model is also used to calculate the flexural rigidity of sandwich samples with different skin thicknesses to check the accuracy of the model and to understand the effect of skin thickness on the predicted mechanical performance of sandwich structures. The effect of heat treatment on the mechanical behavior of sandwich structures is investigated as well.

Open pore foams can be used as gas filters, catalyst supports, and heat exchangers due to their high gas permeability and heat conductivity. In this study, Ni-Cr skins were deposited on each side of a foam sheet by HVOF spraying to form a sandwich structure for use as a heat exchanger. The microstructure of the skins and the interface with the nickel foam struts were examined and the hydraulic characteristics and heat transfer properties of the sandwich structure were experimentally determined. Pressure drops across the heat exchanger were measured and found to be proportional to the square of the velocity of the coolant and a least square fit was used to solve for the permeability, K, and form coefficient, C, of the foam.

Nickel-based superalloys can be used at temperatures up to 1050 °C in air. Superalloy open cell foam sheets with skin layers plasma sprayed on both sides can be used as high temperature heat exchangers provided that the two deposited skins are dense and well adhered to the open cell foam. In this study alloy 625 skins were deposited on each side of a sheet of metal foam by APS and HVOF to form a sandwich structure. Two densities of open cell foams, 20 and 10 pores per linear inch (ppi), were used in this study as the core. The initial Ni foam was converted to an alloy composition by plasma spraying aluminum and chromium on the foam’s struts with subsequent diffusion/solutionizing heat treatments before the alloy 625 skins were deposited. The microstructure of the coatings and the interface between the struts and skins was investigated. A layer of Ni-Al alloy was formed near the surface of the struts as a result of the heat treatment. The foam struts were imbedded more deeply into the coatings deposited by HVOF than the coatings deposited by APS.

Especially, composites of aluminium metal foams are of high potential for lightweight applications in automotive, aerospace and general engineering because of their excellent ratio of low weight and high stiffness. To fulfill the industrial need for these new materials as soon as possible, a new integrated manufacturing process concept has been developed and studied at our institute. The new “easyFoam-process” concept consists of four basic steps: production of semi-finished parts via the powder metallurgical route, forming of the foamable semi-finished part into a near net shape by extrusion or any standard aluminium-forming process, coating of the surface by thermal spraying and foaming by inductive heating. Thus it’s feasible to provide a fast, continuous and efficient production of metal foam composites with highly reproducible properties, resulting in eminent advantages over current techniques for foam sandwich production in terms of degree of anisotropy, statistical spread in foam properties and production economy. This process is also the only one being able to produce a graded pore structure in symmetrical parts of PM-aluminium foams. The thermally sprayed coatings serve simultaneously as mould and as future multifunctional coating. In this paper, some results of our first study in coating the foamable Al-tubes and inductive heating the coated parts are presented.

Beams of a hardenable aluminium foam were coated using electric arc spraying. AlSi6 and XCr13 were sprayed using compressed air or nitrogen. Subsequently the aluminium foam – coating - composites were post treated. The post treatment comprised of a heat treatment, suitable for hardening of the foam, grinding, shot-peening and / or sealing of the coating. Young’s moduli of the composites were non-destructively measured by resonant frequency. The dynamic properties of the composites were investigated by four-point-bending fatigue tests. The influence of the different post treatments on the bending stiffness and the fatigue behaviour was analysed using a statistical approach.

Various methods of making metallic foams and sponges have been studied, although the materials have not yet been put to commercial use. For foams produced using powder metallurgy, this is largely due to the poor surface quality and limited wear resistance. With thermal spray coatings, however, the foams can be upgraded to lightweight composites with defined surfaces, high wear resistance, and significantly increased strength. In this paper, commercial aluminum foams with closed cells and a closed foaming skin are coated with metal and ceramic layers by means of electric arc and plasma spraying. The coated foams are characterized based on their microstructure and the results of uniaxial compression testing. Paper includes a German-language abstract.

Scientist and engineers show an increasing interest in metal foams. Recent activities are not only limited to the different techniques which already exist to produce and characterise metal foams, but also focus on further steps that these fairly new materials have to pass before entering mass production. Metal foams do not possess a high strength; to increase their mechanical properties and to improve the surface finish, thermally sprayed coatings can be applied. A metal foam is mainly characterised by its alloy composition, its density and the size and shape of the cells and pores. The quality of the coating depends on the coating material, the chosen process, the preparation of the surface, spraying parameters and the adhesion of the coating. The main focus of this paper is to reveal the necessary requirements to realise a sound composite made of a thermally sprayed coating onto metal foam. Basic investigations are carried out and during a later stage of the project parameters are to be identified which allow to describe the properties of the new composite material. The priority within this project will be on aluminium foams.