Behaviour and constitutive modelling of ductile damage of Ti-6Al-1.5Cr-2.5Mo-0.5Fe-0.3Si alloy under hot tensile deformation

In this paper, the flow softening and ductile damage of TC6 alloy were investigated using a uniaxial hot tensile test with deformation temperatures of 910 degrees C similar to 970 degrees C and strain rates of 0.01 s(-1)similar to 10 s(-1). Scanning electron microscopy (SEM) was performed on the deformed specimens to reveal the damage mechanism. The results showed that the flow stress rapidly increases to a peak at a tiny strain, followed by a significant decrease due to flow softening and ductile damage. The ductile damage of the studied TC6 alloy can be ascribe to the nucleation, growth and coalescence of microdefects, and the microvoids preferentially nucleate at the interface of the alpha phase and beta matrix due to the inconsistent strain. Then, a set of unified viscoplastic constitutive equations including flow softening and ductile damage mechanisms was developed and determined, and this set of equations was verified by the experimental flow stress, which indicated the reliability of the prediction. Furthermore, the predicted normalized dislocation density and the adiabatic temperature rise increase with decreasing temperature and increasing strain rate. The predicted damage components show that the microdefects mainly nucleate in the initial stage, but then primarily grow and link together with continuing deformation. (C) 2018 Elsevier B.V. All rights reserved.