Rapid solid-state synthesis of titanium aluminides

Intermetallics, such as the titanium aluminides, hold promise for high-temperature structural applications if their ductility can be improved by making fine-grained materials. An important step toward this goal is the rapid synthesis of finely divided powders via simple chemical processes. Here, single-displacement reactions between varying ratios of the metal halides TiCl3 and AlCl3, utilizing Mg as a reducing agent, enables the rapid synthesis of Ti3Al, TiAl, and TiAl3 upon initiation with a heated filament. Reaction temperatures and propagation rates are measured using in situ thermocouples and electrodes. This leads to insights into the propagation mechanism for intermetallic formation in these displacement reactions. Once the sublimation temperature of AlCl3 (178 degreesC) is reached, propagation accelerates rapidly. The reaction temperature exceeds 1000 degreesC within 700 ms. Propagation velocities on the order of 0.5 mm/s are observed. Redox reactions that begin during propagation create electrical signals, which confirm that initiation of chemical processes occur upon the sublimation of AlCl3. Microwave heating was found to be another effective method to initiate these reactions and leads to the formation of phase pure TiAl which is not obtainable as a single product via filament initiation. Powders of TiAl3 can also be produced through reactions between LiAl and TiCl3.