Microstructural evolution and mechanical properties of hot-rolled Ti-30Zr-5Al-2.5Sn alloy with mixed α and α′ phases

Abstract

Ti-30Zr-5Al-2.5Sn (TZAS, wt. %) is a novel α-type Ti-Zr based alloy. Herein, the effect of phase and microstructure evolution on mechanical properties of hot-rolled TZAS alloy with mixed α and α′ martensite phase were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and statistical analysis. The content of primary α phase decreased as the hot-rolling temperature increased from α to α+β region. When the rolling temperature increased to 875 °C, the predominant phase transformed from α phase to α′ martensite phase. The spheroidization degree of TZAS alloys increased with rolling temperature until 850 °C. As the rolling temperature increased from 775 °C to 825 °C, the yield strength gradually enhanced, attributing to the synergistic effect of grain-boundary strengthening, dislocation strengthening and second-phase strengthening from martensite. While, as further increase of rolling temperature, the coarsen primary α grains led to the decrease of yield strength. A peak yield strength of 1038 ± 26 MPa and total elongation of 14 ± 0.6% were obtained after rolling at 825 °C. One should note that work hardening was also a key factor for the alloys strengthening. Furthermore, the fracture mechanisms of studied alloys were also discussed in depth.