Effect of Cell Size on the Microstructure and Mechanical Properties of Hollow Alumina Spheres-Ductile Iron Syntactic Foams

Cellular metals and metallic foams as a class of new engineering materials have unique properties and thus, these materials can be successfully used in many industrial applications. In this study, hollow alumina spheres were used to create cells and cell walls in ductile iron. Alumina hollow spheres were manufactured by polystyrene beads as the substrate and using the coating the polystyrene beads by mixture of alumina powder and sodium silicate as binder. Sand casting technique was used to produce ductile iron syntactic foams. In this technique, alumina hollow spheres were placed into the mold cavity and then, the molten metal was poured. Casting specimens were grinded and then, light microscopy, scanning electron microscopy evaluations, and compression testing were carried out. The results were shown that reduced cell sizes, improved compressive behavior of casting foams. The microstructure of casting specimens consisted of pearlite and ferrite surrounded nodular graphite. In the specimens with smaller alumina hollow spheres, the thickness of the cell walls decreases and cooling rate increases. Therefore, carbide phases were formed in microstructure.