Relationship between β→α dynamic transformation and dynamic recrystallization under thermomechanical coupling in Ti-5Al-5Mo-5V-1Cr-1Fe alloy

Abstract

The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were performed within the range of deformation temperatures of 710–860 °C and strain rates of 0.001–1 s–1. Based on electron backscatter diffraction (EBSD) characterization and analysis technology, the interaction between dynamic phase transformation (DPT) of β-to-α and dynamic recrystallization (DRX) under thermal-mechanical coupling is deeply and systematically explored. We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation. The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery (DRV) deviates more from Burgers Orientation Relationship (BOR) than the α-phase that precipitates near {111}β as temperature increases. The proportion of α-phase precipitated by strain-induced on β recrystallized equiaxed grains for the deviating angle from BOR (θBOR) in the range of 20°–30° increases to 40% with the increase of strain rates below 800 °C. In addition, the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation, which undergoes continuous dynamic recrystallization (CDRX), exhibiting epitaxial recrystallization, namely {110}β//{0001}α. Furthermore, the morphology of grain boundaries α phase (αGBs) precipitated by strain-induced phase transformation (SIPT) on specific types of β grain boundaries (βGBs), as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated. The orientation relationships between α variants in {111}β grain are related with each other by 50°–60°/<–12–10> and 60°–70°/<–48–43> rotation. The “necklace” αGBs of recrystallization exhibit mainly the rotation of 50°–70° around the 〈2–310〉 zone axis, while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12−30>. In summary, the study has contributed to a deeper understanding of the deformation behavior and DPT laws of β-to-αp in near-β titanium alloy, which lays a foundation for the optimization of the hot deformation process and mechanical properties.