Design and microstructure control of Al-doped in-situ TiC reinforced titanium matrix composites

New type of Al-doped TiC-reinforced titanium matrix composite (TMC) was fabricated using a combination of melting-casting and in-situ reaction methods. The microstructure of the TMCs was tailored via forging and annealing treatments. The microstructure of the titanium matrix and reinforcements in TMCs with varying Al contents were systematically characterized using SEM, TEM, and EDS techniques. Abundant in-situ TiC reinforcements formed in the as-cast TMCs across all Al content levels. The morphology of the TiC reinforcements was significantly altered by Al content: increasing Al content promoted the formation of primary TiC while inhibiting the formation of long strip-shaped eutectic TiC. The forging process distinctly regulated α phase precipitation in the matrix, as well as the morphology and distribution of in-situ TiC. Specifically, TiC reinforcements in forged TMCs exhibited short rod-like and near-equiaxed morphology. Furthermore, the microstructure of the titanium matrix was controlled by annealing treatments at different temperatures. Annealing at 700°C and 800°C notably enhanced α phase precipitation, whereas numerous acicular α' martensite grains formed at 900°C. Elemental analysis indicated that the Al concentration in TiC increased with rising Al content in the TMCs, a trend scarcely affected by forging or annealing treatments. Theoretical calculations demonstrated that Al atoms most likely occupy C vacancies in the TiC lattice, thereby inducing lattice expansion of TiC. The effects of Al doping on TMC microstructure and the corresponding microstructure control strategies are also discussed in this study.