Synthesis of γ-TiAl foils and sheets by innovative reactive diffusion methods from elemental Ti and Al

A liquid reaction route and a solid reaction route are developed to fabricate dense γ-TiAl foils and sheets. Sheets were prepared by a one-stage annealing of Ti–Al sandwiches made from two Ti sheets either side of one Al sheet. While annealing above the melting point of TiAl3 results in an inhomogeneous sheet thickness and Al content, a sheet with homogeneous thickness and Al distribution is obtained after annealing below this temperature. Dense γ-TiAl foils were prepared by a two-stage annealing of diffusion bonded sandwiches with aluminum as the outer layer. Depending on the annealing temperature, near-γ, layered γ–α2, layered duplex, or lamellar microstructure can be obtained. The first-stage annealing is below the melting point of aluminum and the second-stage annealing temperature is above 1000 °C. A corrugated γ-TiAl foil was prepared by diffusion welding, corrugation at room temperature and final two-stage reactive diffusion. The reaction mechanism involved in both routes, such as the porous TiAl3 layer formation, the consolidation of the porous TiAl3 layer, the formation of Al inclusions, voids and an irregular TiAl3 layer in the first-stage annealing, and the disappearance of voids and formation of surface cracks in the second-stage annealing was investigated and discussed.