Tri-modal microstructure and performance of TA15 Ti-alloy under near-β forging and given subsequent solution and aging treatment

For TA15 Ti-alloy two types of tri-modal microstructures with excellent comprehensive mechanical properties were obtained via a new approach, near-β forging combined with the solution and aging treatments (SAT), regardless of whether there was a short time of air cooling (AC) during forgings transferring in practice before water quenching. Performance of tri-modal microstructure, with different morphologies and contents of constituent phases (primary equiaxed αp and secondary lamellar αs), was investigated. More and larger αp contributes to higher plasticity, while more and thicker αs benefits for room and high temperature strengths and impact toughness. The formation of tri-modal microstructure via near-β forging+SAT was investigated. AC may change the formation process of lamellar αs and the stored distortion energy in as-forged specimen, and further results in more and larger αp and fewer and thinner αs in final tri-modal microstructure, leading to lower strength but higher plasticity and fracture toughness. The dependences of near-β forging conditions on the obtained tri-modal microstructure via near-β forging and SAT were revealed. The tri-modal microstructure and its performance for service need can be adjusted via control of air-cooling time before water quenching combined with near-β forging conditions selection.