Tri-modal microstructure evolution of TA15 Ti-alloy under conventional forging combined with given subsequent heat treatment

For TA15 Ti-alloy, conventional forging combined with subsequent heat treatment provides a new method to obtain a tri-modal microstructure (consisting of about 20% equiaxed αp, 50-60% lamellar αs and transformed β matrix) possessing attractive comprehensive properties, and it is expected to solve the problems (such as, deformation temperature control, microstructure coarsening, or special requirement for the original microstructure) caused by using the existing method. In this paper, the forming process and principle of obtaining a tri-modal microstructure under conventional forging combined with given subsequent near-β and two-phase field heat treatments (NTH, i.e. 975 °C/30 min/WQ + 930 °C/100 min/AC) were investigated. Meanwhile, taking the volume fraction and morphology of equiaxed αp and lamellar αs as targets, the tri-modal microstructure evolution under different conventional forging conditions (deformation temperatures, deformation degrees, strain rates, cooling modes) and significance of influencing factors were revealed.