Effect of different initial lamellar plate thicknesses on grain refinement and superplastic behaviour in HPT-processed Ti-6Al-4V alloy

Ti-6Al-4V alloy was heated to above the β phase transformation temperature with two different cooling speeds: air cooling and furnace cooling, in order to generate a full thin lamellar structure and a fully coarse lamellar structure, respectively. Then the alloy in two heat-treated conditions was processed at room temperature up to 10 turns by high-pressure torsion (HPT) processing. Investigations were carried out to study the effect of the different initial lamellar plate thicknesses on the microstructure development during HPT processing, and the corresponding superplastic behaviour at the selected low testing temperatures of 773 - 923 K