Flow characteristics and deformation mechanisms for TiAl/Ti₂AlNb diffusion bonded joint

The hot deformation behavior and deformation mechanism of TiAl/Ti₂AlNb diffusion bonded (DB) joint in the temperature range of 900 °C–1000 °C and strain rate range of 0.001 s⁻¹∼0.1s⁻¹ were investigated by isothermal compression tests. The deformation may be related to the coordination deformation of the two alloys，with the deformation of Ti₂AlNb section coming firstly, followed by TiAl due to the existence of the DB interface. The flow behavior of DB joint can be expressed by the hyperbolic sine constitutive equation, and the calculated deformation activation energy Q is 343.5 kJ/mol. The Q value is almost equal to lattice diffusion coefficient (265–331 kJ/mol) in O + B2 Ti₂AlNb alloy, which suggests the deformation mechanism could be controlled by lattice diffusion. Microstructure observation shows that, When deformed at 900°C-0.1s⁻¹, the deformation mechanism is grain boundary sliding accommodated by O-DRX in Ti₂AlNb, γ-DRX in TiAl, deformation twin and β→α₂ phase transformation. While the deformation mechanism is dislocation slip accommodated by β+O→ε phase transformation，ε-DRX，β-DRX in Ti₂AlNb and deformation twin when deformed at 1000°C-0.001s⁻¹. Besides, the 3D processing map of TiAl/Ti₂AlNb DB joint were obtained with deformation temperature and strain rate. There are no flow instability regions of DB joint and the optimum processing parameters were determined to be 1000°C-0.001s⁻¹, favoring development of a new structural component.