Brazing of composite metal foams

Composite Metal Foams (CMFs) forgo the irregular porosities of conventional metal foams in favor of an array of similarly sized hollow metal spheres bolster by an interstitial metal matrix, allowing uniform deformation and outstanding energy absorption. These properties are valuable in high-strength structural applications but compatibility between existing solid metal joining processes and CMF needs to be further understood. Recent projects have shown solid-state joining techniques to be effective in bonding CMFs over a broad range of processing parameters, physical variation, and manufacturing histories. CMFs with thicknesses up to 25 mm were successfully welded through induction welding and up to 50mm by diffusion bonding. This study investigates the performance of CMF, varying in density, and thicknesses joined by brazing with either pure Cu or BNi-2 brazing alloy interlayers. Uniaxial tensile tests on brazed samples resulted in ∼20–48 MPa tensile strength for Cu-brazed samples and ∼24–40 MPa for BNi-2-brazed samples. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) observations were used to study interfacial diffusion and their impact on mechanical performance of bonded parts. Both braze materials successfully bonded S-S CMF of ∼22 mm to ∼42 mm thickness while largely avoiding any significant debonding at the brazed line. The CMF specifications including its density appear to be driving factors in braze joint strength. In general, the majority of samples fractured away from the bond line, indicating strong integration of the fillers into the CMF with consideration for material selection and well-controlled processing.