Constitutive modeling hot tensile behavior of Ti6Al4V alloy by considering phase transformation and damage mechanisms

The hot tensile and fracture behavior, as well as damage mechanisms of Ti6Al4V alloy are investigated by the hot tension tests and microstructure observation experiments. For comprehensively characterizing the hot tensile behaviors, a developed dislocation density-based constitutive model was established by coupling the flow soft -ening, phase transformation and damage mechanisms. The results show that the flow stresses under the relatively high strain rates (0.01-1 s-1) easily peak at low strains and then decrease with the further straining. However, under the low strain rate (0.001 s-1), the flow stress tends to a continuously increasing trend until fractured. After hot deformation, the fraction of beta phase greatly increases compared to that under the initial state. Meanwhile, beta-phase fraction increases with the strain rate decreasing or the deformation temperature increasing. The great input thermal energy by the high temperature and the long deformation period under low strain rates promote the alpha-beta phase transformation. Furthermore, the necking diffusion caused by dislocation motion en-hances the homogeneous deformation under low strain rate or high temperature. The cavitations preferentially nucleate at the alpha/beta phase interface due to the inconsistent strain. The comparison of the measured and calculated results confirms the excellent prediction ability of the established model in reproducing the hot tensile behavior, beta-phase fraction and damage evolution under different processing parameters.