Fabrication of low-density ferrous metallic foams by reduction of chemically bonded ceramic foams

Abstract

Closed cell ferrous foams were fabricated using a chemically bonded oxide ceramic foam precursor. The major constituent of the ceramic foam precursor was iron oxide (Fe 2O 3), which was mixed with various foaming/setting additives. The density of the foam was modified by varying the ambient pressure under which foaming was carried out. Further, a magnesium-ammonium phosphate-based cement system was utilized to promote more rapid setting times and hence minimize foam collapse. The oxide foam was then reduced by heating at 1240°C in a non-flammable hydrogen/inert gas mixture to obtain metallic foams. The relative density of samples foamed under a reduced pressure ( ∼ 380 Torr) was 0.13±0.006, which is the lowest value reported to date for a closed cell ferrous foam. A relative density of 0.21±0.01 was achieved for samples foamed under atmospheric pressure. With regard to the foam morphology, the average cell diameter was 1.41±0.6 mm for the low-density (LD) foams, and 0.96±0.2 mm for the high-density (HD) foams. The iron foams were tested in compression and yielded an average compressive strength of 11±1 and 19±4 MPa for the LD and HD foams, respectively. A comparison based on a bending strength performance index showed that the properties of the ceramic-precursor-derived foams compared favorably with those of steel foams fabricated by other techniques. © 2006 The American Ceramic Society.