Interface characteristic and mechanical performance of TiAl/Ti₂AlNb diffusion bonding joint with pure Ti interlayer

Solid-state diffusion bonding (DB) of TiAl alloy and Ti₂AlNb alloy was carried out using pure Ti as an interlayer at 1000 °C under 20 MPa for 60–120 min. The effects of bonding times on the interfacial microstructure and mechanical performance of the TiAl/Ti/Ti₂AlNb bonded joints at room temperature (RT) were investigated detailly. The results demonstrated that the diffusion layers (DLs) mainly consisted of four characteristic layers, (I) single coarse α₂ phase adjacent TiAl alloy, (II) single refined α₂ phase at the bonding interface, (III) equiaxed/acicular α₂ phase embedded in β phase adjacent Ti₂AlNb alloy and (IV) both equiaxed α₂ phase and acicular O phase embedded in β phase adjacent Ti₂AlNb alloy, respectively. The thickness of the four layers increased with the increasing of the bonding time. The growth of DLs is controlled by diffusion and the reaction rate constant k for region I, II, III and IV are 1.22 × 10⁻⁶, 1.27 × 10⁻⁶, 2.6 × 10⁻⁷ and 7.7 × 10⁻⁷ m·s^−1/2, respectively. Meanwhile, the interface α₂ grain grows up without texture. The maximum tensile strength of 281 MPa was maintained at 1000 °C for 90 min under the pressure of 20 MPa. Consequently, the phase transformation and dynamic recrystallization behavior of the DLs were discussed.