Microstructural evolution in ultrafine-grained Ti-6Al-4V alloy processed by high-pressure torsion

A commercial cold-rolled Ti-6Al-4V sheet was subjected to1073K/1h+823K/3h AC, and equiaxed αphase and very little lamellar structure was obtained. The processing by HPT was performed at room temperature with a pressure of 6.0 GPa and a rotation speed of 1 rpm. Processing of the material was conducted through total numbers of revolutions, N, of 1/4, 1/2, 1, 2, 5, 10 and 20. The dislocations increase with the increasing numbers of turns, grain refinement is achieved and the grains are reasonably equiaxed and uniformly distributed with an average size of ~100 nm. There is a typical logarithmic function relation between the microhardness values and the numbers of the turns. In addition, the microhardness values and the corresponding equivalent strain were linear