The Mechanism and Difference of Superplastic Deformation Microstructure of SP700 Ti‐Alloy Sheet with Two Kinds of Thickness

SP700 is a novel dual‐phase titanium alloy. To elucidate the superplastic deformation mechanisms of SP700 sheets with two different thicknesses, constant strain rate tensile tests were conducted on 0.8 and 2.0 mm specimens at temperatures ranging from 755°C to 815°C and strain rates between 10 ⁻² and 10 ⁻⁴ s ⁻¹ . Results show that the maximum elongation was achieved in the 0.8 mm specimen deformed at 775°C and 10 ⁻³ s ⁻¹ . The strain rate sensitivity index decreased with increasing strain and temperature. Scanning electron microscopy (SEM) reveals that, under a constant strain rate, both the α grain size and volume fraction initially decrease, then increase, and subsequently decrease again with rising temperature. At a constant temperature, α grain size decreased continuously with increasing strain rate, while the volume fraction first increased and then decreased. A more uniform distribution of α‐phase grain sizes in the range of 0.5 μm to 4 μm is associated with superior elongation. Transmission electron microscopy (TEM) indicates that grain boundary sliding, accompanied by dynamic recrystallization, dominates the deformation in the 0.8 mm, leading to significant superplasticity. In contrast, dislocation slip coupled with grain boundary sliding acts as the dominant mechanism in the 2.0 mm. This study provides theoretical support for the SP700 superplastic forming process.