Reaction bonded silicon nitride foams: The influence of iron disilicide on microstructure and mechanical strength

Abstract In this study open-cell reaction bonded silicon nitride (RBSN) foams with high and controlled level of porosity have been produced based on the wet processing of Si-PMMA suspensions in the presence of iron disilicide (FeSi 2 ) as an additive. The investigation focuses on the effect of FeSi 2 on the mechanical strength, nitriding mechanisms, and microstructure of the RBSN foam. The nitriding reactions and the foam microstructures and properties were investigated under various nitriding conditions and for different FeSi 2 contents. It was observed that 1 wt% FeSi 2 significantly increases the strength of the RBSN foams regardless of the nitriding temperature and atmosphere. The nitriding conditions have a strong influence on RBSN foam strength. The maximum strength was achieved under a N 2 atmosphere at 1390 °C with a foam porosity of 71 vol%. The high porosity level of the foam significantly affects the nitriding mechanisms and consequently the foam microstructure, compared to “dense” RBSN ceramics. FeSi 2 promotes the formation of both α- and β-Si 3 N 4 phases depending on its concentration and its addition also increases the whisker content of the foam microstructure due to an increase in SiO and Si vapor formation.