Evolution of Lamellar in Ti6242S Ti-Alloy After -Forging Combined with Two-phase Zone Heat Treatment

The Ti6242S Ti-alloy was processed through beta-forging combined with a two-phase zone heat treatment to investigate the effects of deformation and heat-treatment conditions on the final lamellar alpha phase. It was found that by increasing the deformation degree, the thickness of lamellar alpha was increased, while its volume fraction first increased and then decreased. This is because a larger deformation will result in more distortion energy, and promote nucleation and growth of lamellar alpha, leading to an increase in its volume fraction. When the deformation degree reached 70%, coarsening and spheroidization occurred in some lamellar alpha via cylinderization and boundary splitting during subsequent heat treatment, and resulted in an increase in the thickness and a decrease in the volume fraction of the lamellar alpha. A larger deformation resulted in more low-angle grain boundaries and made the high-angle grain boundaries gradually become continuous, and promoted the precipitation of lamellar alpha with a rotation axis of [(10) over bar 5 5 (3) over bar]/63.26 degrees. Increasing the two-phase zone heat-treatment temperature promoted the alpha -> beta phase transformation and the lamellar alpha growth in length and thickness. Increasing the holding time, martensite decomposition, primary alpha dissolution, and lamellar alpha precipitation occurred, resulting in an increase in the lamellar alpha volume fraction.