Effect of Fe addition on self-propagating high-temperature synthesis of Ti_5Si_3 in Fe-Ti-Si system

摘要

The effect of Fe addition on the SHS reaction products of Fe-Ti-Si system was investigated. When Fe content is 0 wt. percent, the product only consists of Ti_5Si_3 . As the Fe content ranges from 10 to 30 wt. percent, besides Ti_5Si_3 and Fe phases, the transient Fe_2Ti is also found in the final products. With a further increasing Fe content of 40 or 50 wt. percent, however, in addition to Ti_5Si_3 , Fe and Fe_2Ti phases, the FeSi phase is also detected. Furthermore, the contents of Fe_2Ti and FeSi phases as well as the solubility of Fe in Ti_5Si_3 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. percent, theTi_5Si_3 exhibits cobblestone-like shape. When Fe content is increased to 30 wt. percent, the Ti_5Si_3 particulates are finer and most of them are surrounded by the bonding agents. As the Fe content is further increased to 50 wt. percent, it is difficult to distinguish Ti_5Si_3 particulates from Fe and its compounds. The Ti_5Si_3 particulate sizes decrease from more than 6 to about 0.6 |xm or less when Fe content in the preforms ranges from 10 to 50 wt. percent. 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 Ti_5Si_3 formation during SHS reaction process. The formation mechanism of Ti_5Si_3 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 Ti_5Si_3 particulates, as well as the presence of growth striation on the surface of Ti_5Si_3 particulates.