Deformation mechanism and mechanical properties of a thermomechanically processed β Ti-28Nb-35.4Zr alloy.

The effects of thermomechanical treatment on the microstructure and mechanical properties of a newly developed β titanium alloy, i.e., Ti-28Nb-35.4Zr (wt%, hereafter denoted Ti-Nb-Zr) were investigated. The as-cast Ti-Nb-Zr alloy was subjected to solution treatment at 890°C for 1h, after which its thickness was reduced by 20%, 56%, 76%, and 86% via cold rolling. Results indicated that annealing at 890°C for 1h after cold rolling at a thickness reduction ratio of 86% resulted in a phase transformation from the stress-induced α" and ω into β, leading to a recrystallization of a uniform single β phase. The recrystallized Ti-Nb-Zr alloy exhibited a tensile strength of 633MPa, Young's modulus of 63GPa, and elongation at rupture of 13%, respectively. The cold rolled specimens showed a higher Young's modulus than that of the recrystallized specimen due to the stress-induced ω phase. Transmission electron microscopy (TEM) analysis revealed that ω, α" and β phases co-existed in the microstructure of the cold-rolled specimens. Electron backscatter diffraction analysis revealed that the deformation mechanisms during thermomechanical processing included kink bands, {332}<113> twins and shear bands; and the predominant deformation mechanism depended on the extent of CR deformation.