Superplastic forming of titanium alloys at 700°C

Abstract

The formability of the novel Ti-1.5Al-1.5V-2.75Fe-3.0Mo-0.25Ni-0.1B alloy and the commercial Ti-6Al-4V alloy at 700°С was evaluated in the present study. Experiments have demonstrated the possibility of superplastic forming of both alloys with a fine-grained microstructure at 700°C and a constant argon gas pressure p = 2 MPa. However, the forming time for the novel alloy was only a few minutes (τ = 235 s), while for the Ti-6Al-4V it amounted almost 2.5 hours (τ = 8700 s). The better formability of the novel alloy at 700°С compared to the commercial one is in good agreement with the results of computer simulations performed earlier and is mainly due to an increased content of the β phase. Microstructural analysis showed that low-temperature superplastic forming was accompanied by the development of spheroidization and recrystallization processes. It is important that recrystallization did not lead to a significant grain growth and provided an increase in the structure homogeneity and randomization of the rolling texture. The most significant improvement of microstructure homogeneity after forming at 700°C was observed in the Ti-6Al-4V alloy with the initial partially recrystallized structure.