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

摘要

For TA15 Ti-alloy two types of tri-modal microstructures with excellent comprehensive mechanical properties were obtained via a new approach, near-P 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 α_p and secondary lamellar α_s), was investigated. More and larger α_p contributes to higher plasticity, while more and thicker α_s 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 α_s and the stored distortion energy in as-forged specimen, and further results in more and larger α_p and fewer and thinner α_s 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.