Microstructure refinement in near-α/Ti₂AlNb gradient transition zone by laser deposition-hot deformation hybrid manufacturing

Gradient titanium alloys, formed by joining dissimilar alloys, integrate superior properties from both ends, yielding enhanced service performance compared to individual alloys. The intrinsic nature of additive manufacturing demonstrates advances in fabricating gradient titanium alloys by smoothing the gradient transition zone (GTZ) in between, thereby avoiding the hard interfaces typical of traditional joining methods. However, additive-manufactured GTZs inevitably exhibit coarse grains that limit their mechanical properties. In this study, the superior microstructure refinement of a near-α/Ti₂AlNb GTZ is achieved through a hybrid manufacturing approach that combines laser deposition with subsequent hot deformation. Results demonstrate that continuous dynamic recrystallization (CDRX) dominates microstructure refinement over discontinuous dynamic recrystallization ( DDRX) across all deformation parameters. The CDRX is governed by its interaction with O phase. Specifically, nano-sized O phase preferentially precipitated to low-angle grain boundaries at low strains, effectively pinning boundary migration and suppressing CDRX. The pinning effect weakens with increasing strain, allowing CDRX to proceed. The grain refinement map is established as the function of strain rate and temperature, which sheds light on the fundamental understanding of microstructure refinement in titanium and gradient titanium alloys via additive-hot deformation hybrid manufacturing.