Influence of Al addition on the products of self-propagating high-temperature synthesis of Al–Ti–Si system

Influence of Al addition on the products of self-propagating high-temperature synthesis (SHS) reaction in Al–Ti–Si system is investigated. When Al content is 0 wt.%, the product only consists of Ti5Si3. When the Al addition is varied over the range of 5–15 wt.%, the TiAl3 phase appears along with the Ti5Si3 phase. Besides Ti5Si3 and TiAl3, the transient phase Ti5Si4 is also detected in the final products when Al content increases over the range of 20–40 wt.%. However, both the Ti5Si3 and Ti5Si4 phases disappear completely when Al content further increases to 50 wt.%; only TiAl3 phase and trace of Al exist in the final products. Moreover, increase in Al content causes a decrease in Ti5Si3 and an increase in TiAl3 amount, which indicates that Al not only serves as a diluent but also participates in the SHS reaction process. Furthermore, the solubility of Si in TiAl3 increases significantly with Al addition increasing, while that of Al in Ti5Si3 mainly depends on the Al content in the Al–Ti–Si system. In addition, the Al incorporation has a great effect on the microstructure formation and evolution of the SHS reaction products. When Al content is less than 15 wt.%, the final product mainly consists of Ti5Si3; however, which changes into Ti5(Si,Al)3 as Al content increases to 20–25 wt.%, and then turns into another solid solution Ti(Al,Si)3 when Al content further increases to 30–50 wt.%. Consequently, the microstructure evolution may be summarized as follows: Ti5Si3 → Ti5(Si,Al)3 → Ti(Al,Si)3.