The superplasticity and microstructure evolution of coarse-grained Ti40 alloy

The superplastic deformation characteristics of coarse-grained Ti40 alloy have been studied in the temperature and strain rate range of 760–880°C and 5 × 10⁻⁴ to 1 × 10⁻²s⁻¹, respectively. The alloy exhibited good superplasticity in all test conditions except at 760°C and strain rate higher than 5 × 10⁻³s⁻¹, with the maximum elongation of 436% at 840°C, 1 × 10⁻³s⁻¹. The activation energy value was found to be close to the self-diffusion activation energy of Ti40 alloy, suggesting that the rate controlling mechanism was lattice diffusion. The coarse grain was elongated and refined which can be attributed to the occurrence of dynamic recovery and continuous dynamic recrystallisation. These processes were promoted by the subgrain formation and evolution, resulting in the good superplasticity of Ti40 alloy with coarse grains.