Superplastic deformation behavior and constitutive model of TA32 titanium alloy

Abstract:

The mechanical behavior and microstructure evolution of TA32 titanium alloy during superplastic deformation were investigated by uniaxial tensile tests at different temperatures (880~940 ℃) and initial strain rates (5×10-4~1×10-2 s-1). The modified Johnson-Cook constitutive model and BP neural network constitutive model were established. The results indicate that the flow stress and elongation of TA32 titanium alloy are sensitive to temperature and strain rate. The strain rate sensitivity exponent decreases with the increase of strain and increases with the increase of temperature. Increase of temperature and deformation degree promotes the α to β phase transformation and the grain growth of the two phases. Decrease of strain rate moderately increases the grain size of the two phases. The morphology of β phase grains changes significantly with the change of deformation conditions, while α phase grains remains equiaxed. The superplastic fracture mode of TA32 titanium alloy is microporous aggregation fracture caused by the growth and coalesce of cavities. The prediction accuracy of BP neural network constitutive model is higher than modified Johnson-Cook constitutive model under large scale deformation condition.