Coupled behavior of dynamic restoration mechanisms and α phase evolution in TC18 titanium alloy during hot deformation

Hot deformation in the dual-phase region is complicated by the inherent strain incompatibility between the α and β phases, together with the concurrent evolution of dynamic restoration (DR) mechanisms and phase transformation. The strong coupling of these phenomena produces distinct microstructural states that ultimately govern the mechanical response. In this study, the operative dynamic recrystallization (DRX) mechanisms of β grains, their transitions, and their interplay with α-phase evolution were systematically investigated under varying deformation parameters. By quantitatively distinguishing and spatially mapping discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) using EBSD, we show that deformation-induced α-phase spheroidization and the α → β transformation progressively diminish the pinning effect exerted on the original β deformation boundaries. This reduction in interfacial constraint promotes a transition of the β matrix from dynamic recovery (DRV)-dominated behavior toward CDRX-dominated restoration, while the fractional evolution of DDRX and CDRX demonstrates a clear competitive relationship across different deformation conditions. Moreover, the preferred nucleation sites for DDRX were observed to shift from α/β interfaces to β grain boundaries as deformation proceeds. These findings provide fundamental insights into α/β coupling during hot deformation and offer guidance for optimizing thermoforming strategies for near-β titanium alloys. • EBSD multi-criteria and TEM analyses quantitatively distinguish β-DRV, DDRX and CDRX during hot compression. • DDRX and CDRX fractions and spatial distributions are mapped as functions of strain rate and true strain, revealing a transition from DRV- to CDRX-dominated behavior under higher deformation severity. • α-phase evolution driven by α-DRX and deformation-induced α→β transformation modulates β-DRX through Zener-like interfacial pinning. • Schmid factor analysis demonstrates orientation-dependent slip transfer and DRX coordination between α and β phases. • A coupling framework links deformation parameters, α/β morphology evolution and DRX pathway selection in TC18 alloy.