Hot tensile behavior of a TiAl alloy with a (β₀ + γ) microduplex microstructure prepared simply by heat treatments

A (β₀ + γ) microduplex microstructure was prepared in a Ti-42Al-8.5V (at%) alloy by means of quenching-tempering treatments, which was characterized by ultra-fine γ platelets embedded in millimeter-sized β₀ grains according to a definite K-S orientation relationship. Hot tensile tests were performed at 850–1000 °C with strain rates of 5 × 10⁻⁴–5 × 10⁻³ s⁻¹ and a near-superplastic creep behavior was yielded. As a consequence, high elongations (>100%) were obtained with a stress exponent of ~3. Deformation mechanism was further analyzed by examining the microstructure and orientation evolution in individual β₀ grains. The results showed that significant crystal rotation and fragmentation occurred in β₀ matrix due to plastic flow and recrystallization, leading to an equiaxed grain structure with a weak preferential orientation resembling ND fiber where {111}<112>was the dominant component. In contrast, evident globularization/coarsening of the γ platelets was observed during deformation. Meanwhile, the γ platelets were slightly deformed but drifted with the β₀ matrix. The spontaneous rotation due to grain boundary/interface sliding resulted in dramatic orientation divergence of γ phase. A weak and unusual<110>fiber was produced due to the preservation of K-S orientation relationship.