Dislocation density based model for plastic deformation and globularization of Ti-6Al-4V

• A physically based model for the plastic deformation of Ti-6Al-4V is developed.
• The model is calibrated using tests done at various temperatures and strain rates.
• At low & medium temperatures, dislocation glide & climb are the dominant mechanisms.
• At high temperatures, globularization is also dominant.
• The model can reproduce flow softening and stress relaxation behavior in Ti-6Al-4V.

Although Ti-6Al-4V has numerous salient properties, its usage for certain applications is limited due to the challenges faced during manufacturing. Understanding the dominant deformation mechanisms and numerically modeling the process is the key to overcoming this hurdle. This paper investigates plastic deformation of the alloy at strain rates from 0.001 s−1 to 1 s−1 and temperatures between 20 °C and 1100 °C. Pertinent deformation mechanisms of the material when subjected to thermo-mechanical processing are discussed. A physically founded constitutive model based on the evolution of immobile dislocation density and excess vacancy concentration is developed. Parameters of the model are obtained by calibration using isothermal compression tests. This model is capable of describing plastic flow of the alloy in a wide range of temperature and strain rates by including the dominant deformation mechanisms like dislocation pile-up, dislocation glide, thermally activated dislocation climb, globularization, etc. The phenomena of flow softening and stress relaxation, crucial for the simulation of hot forming and heat treatment of Ti-6Al-4V, can also be accurately reproduced using this model.