Synergistic Regulation of Microstructure and Mechanical Property in TiAl Alloys via Rolling and Cyclic Heat Treatment

The presence of the brittle β/B2 phase in TiAl alloys often deteriorates their mechanical properties, posing a significant challenge for manufacturing large-sized, high-performance sheets. To address this issue, this study systematically investigates the synergistic effect of pack rolling and subsequent heat treatment on the microstructure evolution and mechanical properties of a Ti-44Al-4Nb-1.5Mo-0.1B-0.1Y alloy. Sheets with two different deformation levels (R7: 69.8% and R11: 83.0% reduction) were prepared via pack rolling. This was followed by a series of heat treatments at different temperatures (1150–1350 ◦C) and cyclic heat treatments at 1250 ◦C (3, 6, and 9 cycles). The results demonstrate that the higher deformation level (R11) promoted extensive dynamic recrystallization, resulting in a uniform microstructure of equiaxed γ, α2, and β phases, while the lower deformation (R7) retained a significant fraction of deformed γ/α2 lamellae. Heat treatment at 1250 ◦C was identified as optimal for transforming the microstructure into fine lamellar colonies while effectively reducing the β/B2 phase. Cyclic heat treatment at this temperature further decreased the β-phase content to 4.1% after 9 cycles. The elimination mechanism was determined to follow the β→ α → γ + α2 phase transformation sequence, driven by the combined effect of rolling-induced defects and cyclic thermal stress.