Growth Mechanism of TiCx during Self-Propagating High-Temperature Synthesis in an Al−Ti−C System

The different shapes of titanium carbide (TiC x ) grains formed at different growth stages of self-propagating high-temperature synthesis (SHS) were obtained in the quenched sample. The shape evolution of the TiC x grains and the growth mechanism are discussed. As the highly substoichiometric TiC x nucleates at the initial stage of the SHS, the (111) surfaces become stable and the TiC x grains nucleate as octahedra. With an increase of the TiC x stoichiometry, the free energy of the (111) surfaces increases. Hence, the area of the (111) surfaces on the TiC x grains decreases gradually while the (100) surfaces are exposed. The growth shape of the TiC x grains turns to truncated-octahedron. Moreover, when the combustion temperature during the SHS exceeds a certain value (about 1800 °C), the (100) surfaces of the TiC x grains turn round and these rounded (100) regions grow and coalesce with further increasing of the TiC x stoichiometry. The growth shape of the TiC x grains then turns to close-to-sphere.