Hot pack rolling nearly lamellar Ti-44Al-8Nb-(W, B, Y) alloy with different rolling reductions: Lamellar colonies evolution and tensile properties

Abstract

The relationship of the microstructure and tensile properties between the rolling conditions was investigated by fabricating Ti-44Al-8Nb-(W, B, Y) alloy sheets under different rolling conditions. The original nearly lamellar structure with mean colony sizes of 120μm was significantly refined to a duplex microstructure with mean grain sizes of 5–6.1μm. The mechanism of lamellar colonies evolution is discontinuous dynamic recrystallization (DDRX), which occurs at tri-boundaries, phase boundaries, and twin boundaries. The microstructure refinement and uniformity of as-rolled alloys was improved by increasing total reduction. As the total rolling reduction increases from 43% to 72%, the volume fraction of remnant lamellar colonies decreases from 28.5% to 6.8% and newly formed α2/γ lamellar colonies increases from 13.7% to 33.7%. The mean grain sizes of recrystallized grains also can be refined from 5.4μm to 3.6μm. The tensile properties exhibit an increasing trend with the increase of total rolling reduction. When the total rolling reduction is 72%, the alloy exhibits a small fluctuation of mechanical properties. The UTS is higher than 1106MPa with an elongation value of 0.94% at room temperature. At 800°C, the UTS remains as high as 744MPa with an elongation value of over 40%.