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

The effects of thermomechanical treatment on the microstructure and mechanical properties of a newly developed beta titanium alloy, i.e., Ti-28 Nb-35.4Zr (wt%, hereafter denoted Ti-Nb-Zr) were investigated. The as cast Ti-Nb-Zr alloy was subjected to solution treatment at 890 degrees C for 1 h, after which its thickness was reduced by 20%, 56%, 76%, and 86% via cold rolling. Results indicated that annealing at 890 degrees C for 1 h after cold rolling at a thickness reduction ratio of 86% resulted in a phase transformation from the stress-induced alpha and omega into beta, leading to a recrystallization of a uniform single beta phase. The recrystallized Ti-Nb-Zr alloy exhibited a tensile strength of 633 MPa, Young's modulus of 63 GPa, 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 omega phase. Transmission electron microscopy (TEM) analysis revealed that omega, alpha and beta 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.