Synthesis of syntactic steel foam using gravity-fed infiltration

In this study, we report a procedure for producing syntactic steel foams by melt infiltration of millimeter-sized ceramic microspheres. The gravity-fed infiltration method yields steel foam with uniform distributions of microspheres and negligible unintended porosity. The critical parameters in the manufacturing process are the melt temperature and the preheat temperature of the microspheres prior to infiltration. Syntactic foams with relative density of 0.46 were produced using monosized microspheres (4.45 mm) randomly situated in a mold. Six steel compositions were selected to produce steel foams of different inherent yield strength: five ferritic–pearlitic steels and one TRIP steel (transformation-induced plasticity). The resultant foams were characterized by chemical and microstructural analysis. The microstructure of the samples consisted of blends of ferritic and pearlitic constituents in varying proportions for the ferritic–pearlitic steels, while the cast TRIP steel matrix presented an austenitic microstructure. Simple compression behavior of the steel syntactic foams was studied, and the TRIP steel syntactic foam exhibited the highest compression strength and energy absorption capacity. Syntactic steel foams were also produced with different relative densities (0.60, 0.68 and 0.75). The steel syntactic foam with relative density of 0.60 exhibited the maximum energy absorption. Problems and challenges for achieving steel foams with lower relative densities and for scaling up the synthesis process are contemplated.