Formation of Phases in Reactively Sintered TiAl(3) Alloy

This work highlights new results on the synthesis of the TiAl(3) intermetallic phase using self-propagating high-temperature synthesis. This method is considered a promising sintering route for intermetallic compounds. It was found that the reactions proceed in two stages. Below the melting point of aluminum, the Ti(2)Al(5) phase forms at 450 °C after long annealing times by a direct solid-state reaction between the aluminum and titanium, and is converted consequently to TiAl(3). This is a completely new finding; until now, many authors have believed in the preferential formation of the TiAl(3) phase. The second stage, the self-propagating strongly exothermic reaction, proceeds above the melting point of aluminum. It leads to the formation of the TiAl(3) phase accompanied by Ti(2)Al(5) and Ti(3)Al phases. The reaction mechanism was shown in the form of chemical equations, which were supported by calculating Gibbs energy. Reaction temperatures (T(onset), T(maximum), and T(offset)) were determined after induction heating thanks to recording by an optical pyrometer. This finding provides completely new opportunities for the determination of activation energy at heating rates, in which common calorimeters are not able to detect a response or even measure. Now, the whole procedure will become accessible.