Superplastic deformation and microstructural evolution of Ti-6Al-4V alloy

The deformation behavior and superplasticity of Ti-6Al-4V alloy at elevated temperature have been investigated through tensile tests. The microstructures near the fracture of the specimen have been observed by optical microscopy. The results show that the flow stress of Ti-6Al-4V alloy decreases obviously with increasing of the temperature or decreasing of the initial strain rate. The temperature and the initial strain rate of optimal superplastic deformation are 880 ?C and 0.001 s^-1, respectively. Under this optimal condition, the maximum elongation is 689%; however, the peak stress is only 30.03 MPa. During the superplastic tensile deformation, the dynamic recrystallization occurs obviously in the deformation zone of the specimen and the lamellar α grain is broken, refined and spheroidized, so that the superplasticity can be improved. With increasing of the deformation temperature, the deformation amount and the deformation time, the recrystal α grain will merge and grow up, causing obvious coarsening of the microstructure. The temperature of optimal superplastic deformation should not exceed the ceasing temperature of lamellar α→β phase transformation for the α+β titanium alloy with primary α phase and lamellar transformed β phase.