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

Abstract

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 Ti 5Si 3. When the Al addition is varied over the range of 5–15 wt.%, the TiAl 3 phase appears along with the Ti 5Si 3 phase. Besides Ti 5Si 3 and TiAl 3, the transient phase Ti 5Si 4 is also detected in the final products when Al content increases over the range of 20–40 wt.%. However, both the Ti 5Si 3 and Ti 5Si 4 phases disappear completely when Al content further increases to 50 wt.%; only TiAl 3 phase and trace of Al exist in the final products. Moreover, increase in Al content causes a decrease in Ti 5Si 3 and an increase in TiAl 3 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 TiAl 3 increases significantly with Al addition increasing, while that of Al in Ti 5Si 3 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 Ti 5Si 3; however, which changes into Ti 5(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: Ti 5Si 3 → Ti 5(Si,Al) 3 → Ti(Al,Si) 3.