Hot Workability and Superplasticity of Low-Al and High-Nb Containing TiAl Alloys

The superplastic deformation mechanism of low-Al and high-Nb containing TiAl alloy was investigated in compression mode. The experimental results showed that intense dynamic recrystallization (DRX) breaks the balance and leads to a significant drop in flow stress after the peak when deforming below 950°C. Arrhenius kinetic analysis revealed that the activation energy for superplastic compression first increased then decreased with temperature, suggesting a change in the deformation mechanism. Microstructure observations showed that, when deformed at 850°C, the deformation mechanism was grain-boundary sliding accommodated by γ-DRX, γ-intragranular deformation, and β/B2-phase decomposition, while the mechanism was grain-boundary sliding accommodated by γ-DRX, β/B2-DRX, and γ → β/B2 + α₂ phase transformation when deformed at 1000°C. After compression, the microstructure tended to be uniform, which may yield important information for the development of new deformation techniques for TiAl alloys.