The effects of α/β volume fraction on the superplastic deformation behavior of Ti-6Al-4V

Present investigation has been made to study the superplastic deformation behavior of Ti-6AL-4V alloy with respect to the variation of alpha/beta volume fraction. The results have been analyzed by the theory of inelastic deformation which consists of two mechanisms, i.e., the grain matrix deformation and the phase/grain boundary sliding. Grain matrix deformation is found to be dominant at 600 degrees C and well described by the plastic state equation when a permeability parameter, p, is 0.15. Phase boundary sliding becomes dominant at 800 OC and also consistent with the viscous flow equation with M-g=0.5. The flow stress curves for the fine grained structures (3 mu m) are well agreed with the iso-stress model, while those for large grained materials are the mixed mode of iso-stress and iso-strain rate modes. The largest elongation obtained in the 48% beta structure is primarily attributed to the phase boundary sliding occurring predominantly in the microstructure.