Abstract

The foamability of iron‐carbon alloys using the powder metallurgical process route was investigated. Pure iron and carbon powder with an addition of foaming agent were mixed and compacted. The foaming process started during heating the sample as soon as a temperature above the solidus temperature of the iron‐carbon alloy was reached. Result of the process is an iron foam with a porosity of up to 60%. It was investigated, how the foaming behaviour is influenced by the parameters of alloy composition and compaction process. Different foaming agents (alkaline earth metal carbonates and metal nitrides) as well as different carbon additions and compacting processes were tested.It can be seen that sort and amount of foaming agent have an unexpected low influence on the expansion process whereas an increasing carbon content supports the expansion significantly. The use of different compacting processes has only little influence on the expansion itself, but highly effects both the pore distribution and homogeneity. The poor effect of the foaming agent cannot be satisfactorily explained. Investigations of a possibly premature gas emission or of a not gas‐tight inclusion of the foaming agent do not show clear results. The support of the expansion by carbon additions can be attributed to the formation of CO‐gas by the Vacher‐Hamilton law during simultaneous formation of the liquid Fe‐FeC‐eutectic phase. The more inhomogeneous pore structure of iron foams caused by the use of hot‐or hot isostatically pressed semi‐finished products can be traced back to a higher internal gas pressure in the sample which results in a burst of the microstructure of the semi‐finished product.

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