The effect of Zr addition on the microstructure evolution and mechanical properties of hot-rolled TiAlNbZr alloy

Abstract

The microstructure and mechanical properties of hot-rolled Ti–6Al–7Nb-xZr (x = 0, 5, 10, 15, 20 wt%) (TANZ) alloys were systematically studied. Herein, the effects of phase and microstructure evolution on the mechanical properties of hot-rolled TANZ alloy were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and statistical analysis. The addition of zirconium can change the β-phase stabilization ability of TANZ alloy and thus change its phase transformation point. Metastable phases (α′, α″, and metastable β phases) are retained during hot rolling at 850 °C and subsequent water quenching. Furthermore, the recovery of the initial α phase is promoted during hot rolling and holding. During the deformation process, the presence of both the initial α phase and the metastable phase (β transformation structure) is conducive for coordinated simultaneous deformation. The uniform deformation ability and the work-hardening behavior of TANZ alloys are significantly improved by increasing Zr content. The yield strength, true stress in tensile strength tests, and uniform elongation of the TAN15Z alloy are 848 MPa, 1160 MPa, and 9.5%, respectively. The corresponding values for the TAN20Z alloy are 810 MPa, 1331 MPa, and 11.6%, respectively. A significant improvement in the trade-off between strength and plasticity was achieved. Furthermore, the fracture mechanisms of the studied alloys were also discussed in depth.