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

Ti-30Zr-5Al-2.5Sn (TZAS, wt. %) is a novel alpha-type Ti-Zr based alloy. Herein, the effect of phase and microstructure evolution on mechanical properties of hot-rolled TZAS alloy with mixed alpha and alpha' martensite phase were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and statistical analysis. The content of primary alpha phase decreased as the hot-rolling temperature increased from alpha to alpha+beta region. When the rolling temperature increased to 875 degrees C, the predominant phase transformed from alpha phase to alpha' martensite phase. The sphemidization degree of TZAS alloys increased with rolling temperature until 850 degrees C. As the rolling temperature increased from 775 degrees C to 825 degrees 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 alpha 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 degrees 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.