Influence of Fe addition on products of self-propagating high-temperature synthesis (SHS) reaction in 3Ti-Si-2C system was investigated in the present study. Without Fe addition, Ti5Si3 and TiC are the dominant phases along with a small amount of Ti3SiC2 phase and unreacted C left in the final products. As Fe content ranges from 10% to 30%, the products consist of TiC, Ti5Si3, Fe2Ti and unreacted C, but no trace of Ti3SiC2 phase is detected. Furthermore, the amounts of both Fe2Ti and C phases increase with Fe content increasing. Addition of Fe has a great effect on the reaction route and significantly restrains the formation of Ti3SiC2 during the combustion synthesis process, and therefore, the SHS is not an effective fabrication technique to synthesize the ternary Ti3SiC2 ceramic in either 3Ti-Si-2C or Fe-3Ti-Si-2C system. Besides, without Fe addition, Ti5Si3 presents as the coarse irregular appearance with an obviously sintered morphology. In contrast, the shape of Ti5Si3 exhibits more and more spherical (cobblestone-like) and the surface becomes increasingly smooth, because the amount of liquids formed during the SHS reaction increases with the increase of Fe content. On the other hand, with Fe content increasing from 0 to 30 wt.%, the particulate size of TiC decreases from more than 5 μm to 1 μm or less, mainly due to the fact that the combustion temperature decreases with the increase of Fe content in the preforms.
In the present study, by adding SiC particles into AI-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced AI matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in AI matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/AI composites were investigated by using scanning electron microscopy （SEM） and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 pm to 30 μm. The size of primary AI dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fiber-form to a short fiber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no significant change in dendrite arm spacing （DAS） was observed in the presence of SiC particles.
