Microstructure and superplastic deformation for aerospace Ti-alloys associated with α-phase curing behavior

Superplastic deformation behavior of aerospace Ti-alloy (Ti-6.29Al-2.38Sn-2.24Zr-2.59Mo-1.74Cr) with medium grain size has been investigated by using a non-constant strain rate electronic tensile testing apparatus. The optimal superplastic temperatures have been determined in the range of 1133–1193 K, which is about 20–80 K below α solution temperature. The obvious α   phase curing occurred and played an important role during superplastic tension. Meanwhile, microstructural mechanism was characterized into three typical steps, viz., phase curing, dislocation rearrangement and neo-phase formation. The optimal superplasticity was caused by the repeated and in-turned curing and dynamic recrystallization associated with boundary sliding. The grain growth suggested that dynamic recrystallization occurred during superplastic tension. Therefore, the dynamic recrystallization associated with post-curing phase had advantageous to homogeneous deformation. Generally, the post-curing secondary phase with suitable grain size was greatly beneficial on superplasticity, and the maximum elongation that reached 1013% to coarse-grained alloy has been obtained at temperature of 1173 K with initial strain rate of 3.3×10−4 s−13.3×10−4 s−1.