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

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