Comparing the evolution and deformation mechanisms of lamellar and equiaxed microstructures in near β-Ti alloys during hot deformation

This work systematically investigates the microstructural evolution and deformation mechanism of lamellar and equiaxed Ti-55511 alloys during hot deformation. For textural discrepancies, the classical Burgers orientation relationship in lamellar microstructures broke down owing to dynamic recrystallization (DRX) of the alpha phase during hot deformation, while the intensities of micro-textures increased due to the elongated alpha phase parallel to the rolling direction. The anisotropies of the mechanical properties in deformed lamellar microstructures were influenced by the DRX of the alpha phase and inhomogeneous deformation, such as the formation of shear bands. With regard to equiaxed microstructures, dynamic recovery (DRV) of the alpha phase predominated, forming elongated alpha grains perpendicular to the loading direction, which increased the anisotropy. However, the anisotropy from DRV was compensated for by the DRX of the beta phase. DRV alpha grains with serrated boundaries promoted the DRX of the beta phase due to the accumulation of dislocations. The localized shear band found in the lamellar alpha plate during spheroidization comprised two ribbon-like {1 (1) over bar 01} twins, which are abreast but nonparallel and play critical roles in the evolution of alpha phases. The activation of this type of twin is heavily dependent on the aspect ratios of the alpha phases. These studies provide insight into the deformation behavior of lamellar and equiaxed near beta-Ti alloys, which paves the way for the development of ultra-fine-grained microstructures with excellent mechanical properties.