Mechanism dependent strain rate response of dynamic recrystallization in TC18 titanium alloy during hot deformation in the α+β region

Strain rate plays a critical role in governing the hot deformation behavior and dynamic recrystallization (DRX) mechanism of near β titanium alloys. In this study, the mechanism dependent strain rate response of DRX in TC18 titanium alloy deformed in the dual phase region was investigated by uniaxial compression (UC), with supplementary shear compression (SC) at low nominal strain used to clarify the influence of deformation path on the development of distinct DRX pathways. The results demonstrate that the strain rate response of DRX is not uniform, but depends strongly on the active restoration mechanism. Under UC, discontinuous dynamic recrystallization (DDRX) assisted boundary bulging and migration predominated at low strain rates, whereas continuous dynamic recrystallization (CDRX) related intragranular subdivision gradually became dominant with increasing strain rate and strain. In particular, the DRX evolution did not show a simple monotonic dependence on strain rate under all conditions, suggesting a transitional balance between DDRX related boundary migration and CDRX related intragranular subdivision. The concurrent α phase evolution and α/β interfacial effects further contributed to local strain partitioning and β DRX pathway selection. Supplementary SC further reveals that the shear dominated deformation path can further promote CDRX related intragranular reorganization at high strain rate, indicating that β DRX pathway selection is affected by both strain rate and deformation path.