Strain-induced continuous transition from orthorhombic to hexagonal-like phase in Ti-36Zr-6Nb alloy with abnormally high strain hardening

The deformation mechanism of the α″-type Ti-36Zr-6Nb alloy exhibiting an abnormal strain hardening behavior was investigated using in-situ high-energy X-ray diffraction and ex-situ transmission electron microscopy under tensile tests. It was discovered that the orthorhombic α″ phase distorts successively toward hexagonal symmetry during tension through coupled atomic shear and shuffle, and the successive distortion of the α″ lattice contributes to the abnormally high strain hardening of the Ti-36Zr-6Nb alloy. Notably, the orthorhombic α″ phase does not transform into an ideal hexagonal phase during tension but instead transforms into a hexagonal-like phase. The hexagonal-like phase exhibits shear and shuffle components that are very close to those of the ideal hexagonal phase. Additionally, the strain-induced α″ to hexagonal-like martensitic transition was found to be partially reversible during unloading. The present study offers an in-depth understanding of the abnormal strain hardening behavior and the strain-induced phase transition behavior of the α″-type titanium alloys. © 2024 Elsevier B.V.