Low-temperature superplasticity of β-stabilized Ti-43Al-9V-Y alloy sheet with bimodal γ-grain-size distribution

•Superplasticity of TiAl alloy sheet with bimodal grain size distribution at the lowest temperature of 800 ℃ is realised.•Maximum elongation of ~360% is obtained at 900 ℃ with an initial strain rate of 2.0 × 10-4 s-1.•In-situ XRD verifies that there is no order-disorder transformation of β phase during superplastic deformation.•The coordination of dynamic recrystallization and grain-boundary sliding is the main mechanism of superplastic behaviour.