Study on diffusion bonding of composite metal foams

Metal foams are notable for their impressive impact and thermal energy absorption capabilities primarily when compared to bulk metals. Composite metal foams (CMF) exemplify these properties through unchallenged structural uniformity, enhanced by an arrangement of similar prefabricated hollow metal spheres suspended within a metallic matrix. CMF's extraordinary physical, thermal, and mechanical properties make it a prime candidate for replacing bulk materials in various structural applications. However, the use of CMF in larger structures requires the implementation of joining methods. Solid-state joining processes are particularly well-suited for metal foams as they can form solid bonds between porous workpieces without distorting their cellular structures. Previous success was achieved in joining CMF panels up to 2.5 cm thick through induction welding, though localized heating through induced Eddy currents could not fully permeate thicker samples. This limitation has caused a shift in focus to diffusion bonding of CMF panels thicker than 2.5 cm. This process utilizes a vacuum furnace, combining heat with intense pressure to facilitate atomic diffusion between workpieces. This study evaluates the suitability of diffusion bonding in joining CMF panels through a combination of uniaxial tensile tests and scanning electron microscopy (SEM) observations. Tensile testing indicated bond strength to be largely affected by sample density, and in turn, consistency of the steel powder used in CMF production. Overall, diffusion bonding of CMF was successful from thicknesses below 2.5 cm up to 5 cm, with material density and surface preparation being the apparent driving factors to successful bonding.