Fe-Si Intermetallics/Al₂O₃ Composites Formed between Fe-20% Si and Fe-70.5% Si by SHS Metallurgy Method

Fe–Si intermetallics–Al₂O₃ composites were fabricated by thermite-assisted combustion synthesis. Combustion reactions were conducted with powder compacts composed of Fe₂O₃, Al, Fe, and Si. The starting stoichiometry of powder mixtures had an atomic Fe/Si proportion ranging from Fe-20% to Fe-70.5% Si to explore the variation of silicide phases formed with Si percentage. Combustion in the mode of self-propagating high-temperature synthesis (SHS) was achieved and the activation energy of the SHS reaction was deduced. It was found that the increase of Si content decreased the combustion temperature and combustion wave velocity. Three silicide compounds, Fe₃Si, FeSi, and α-FeSi₂, along with Al₂O₃ were identified by XRD in the final products. Fe₃Si was formed as the single-phase silicide from the reactions with Si percentage from Fe-20% to Fe-30% Si. FeSi dominated the silicide compounds in the reactions with atomic Si content between Fe-45% and Fe-55% Si. As the Si percentage increased to Fe-66.7% Si and Fe-70.5% Si, α-FeSi₂ became the major phase. The microstructure of the composite product showed that dispersed granular or nearly spherical iron silicides were embedded in Al₂O₃, which was dense and continuous. Most of the silicide grains were around 3–5 μm and the atomic ratio of silicide particles from the EDS analysis confirmed the presence of Fe₃Si, FeSi, and FeSi₂.