Fabrication and Microstructure of Metal-Metal Syntactic Foams

Abstract : The objective of this paper is to report on the fabrication process and document the microstructure of metal-metal syntactic foams. The composite microstructure consists of thin-wall, hollow Fe-Cr stainless steel spheres cast in various metal matrices including aluminum alloys 6061, 7075, 413, magnesium alloy AZ31B, and unalloyed aluminum and magnesium. Hollow spheres were formed from slurries of fine particle size iron and chromium oxides via the coaxial nozzle process. The oxides were reduced and sintered in hydrogen to the corresponding Fe-Cr alloy. Spheres were sufficiently uniform to allow arrangement into random or periodic arrays. These arrays were infiltrated by an aspiration casting process, resulting in a structure less dense than the matrix metal.