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

Abstract

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.