Effect of Fe addition on self-propagating high-temperature synthesis of Ti5Si3 in Fe–Ti–Si system

The effect of Fe addition on the SHS reaction products of Fe-Ti-Si system was investigated. When Fe content is 0 wt.%, the product only consists of Ti5Si3. As the Fe content ranges from 10 to 30 wt.%, besides Ti5Si3 and Fe phases, the transient Fe2Ti is also found in the final products. With a further increasing Fe content of 40 or 50 wt.%, however, in addition to Ti5Si3, Fe and Fe2Ti phases, the FeSi phase is also detected. Furthermore, the contents of Fe2Ti and FeSi phases as well as the solubility of Fe in Ti5Si3 also increase with the increasing of Fe content. This indicates that Fe not only serves as a diluent, but also participates in the SHS reaction process. Moreover, addition of Fe has a great effect on the microstructures of SHS reaction products. When Fe content is 10 or 20 wt.%, the Ti5Si3 exhibits cobblestone-like shape. When Fe content is increased to 30 wt.%, the Ti5Si3 particulates are finer and most of them are surrounded by the bonding agents. As the Fe content is further increased to 50 wt.%, it is difficult to distinguish Ti5Si3 particulates from Fe and its compounds. The Ti5Si3 particulate sizes decrease from more than 6 to about 0.6 mum or less when Fe content in the preforms ranges from 10 to 50 wt.%. This is mainly due to the fact that the combustion temperature decreases with the increasing of Fe content. The addition of Fe provides more liquid phase for the Ti5Si3 formation during SHS reaction process. The formation mechanism of Ti5Si3 in Fe-Ti-Si system can be characterized by the solution, reaction and precipitation processes. This can be confirmed by the presence of bonding agents (remaining liquids), nearly spherical (cobblestone-like) morphology and relatively smooth surface of Ti5Si3 particulates, as well as the presence of growth striation on the surface of Ti5Si3 particulates.