Influence of Cu addition on the self-propagating high-temperature synthesis of Ti5Si3 in Cu–Ti–Si system

The self-propagating high-temperature synthesis (SHS) reactions can take place in Cu–Ti–Si systems with Cu additions of 10–50 wt.%, and the products only consist of Ti5Si3 and Cu phases, without any transient phase. In Ti–Si system, most of the Ti5Si3 grains synthesized exhibit the polygon-shaped coarse appearance with an obviously sintered morphology. When Cu content increases from 10 to 50 wt.%, however, the Ti5Si3 exhibits cobblestone-like shape with a relatively smooth surface, and its average size decreases significantly from ∼15 to ∼2 μm or less. The formation mechanism of Ti5Si3 in Cu–Ti–Si system is characterized by the solution, reaction and precipitation processes. Furthermore, the addition of Cu has a great influence on the volume change between green and reacted preforms. The volume change increases with Cu content increasing from 0 to 20 wt.%, and then decreases with the content further increasing from 20 to 50 wt.%. The addition of Cu to Ti–Si system significantly decreases the onset temperature of the reaction during differential scanning calorimetry process, which is even much lower than the α → β transition temperature of Ti (882 °C), suggesting that the reaction could be greatly facilitated by Cu addition. As a result, the role of Cu serves not only as a diluent but also as a reactant and participates in the self-propagating high-temperature synthesis reaction process.