Thermal Stability and Lattice Strain Evolution of High-Nb-Containing TiAl Alloy under Low-Cycle-Fatigue Loading

The micromechanical behavior and the effect of temperature on the micromechanical mechanism of high-Nb-containing TiAl alloy during low-cycle fatigue still remain uncertain. Herein, in situ and ex situ synchrotron-based high-energy X-ray (HEXRD) experiment results reveal that the γ and ω_o phases suffer compressive lattice strains but the lattice strain in the α₂ phase evolves from tensile to compressive during low-cycle fatigue at 900 °C. In addition, the three phases suffer compressive lattice strains during cooling to room temperature, which could result in larger compressive lattice strains in γ and ω_o phases and the change of the lattice strain state in the α₂ phase. The peak-broadening results show γ recrystallization is dominant in the interrupted low-cycle-fatigue samples, whereas inhomogeneous deformation occurs in the failed low-cycle-fatigue samples. The performed synchrotron diffraction experiments offer a deeper insight into the phase transformations and micromechanism of TiAl alloy during low-cycle fatigue.