Abstract: The fine and uniform lamellar microstructure plays a crucial role in mitigating the room-temperature brittleness of TiAl alloys. However, such fine microstructures often suffer from insufficient temperature-bearing capacity, and addressing the trade-off between room-temperature (RT) plasticity and high-temperature performance is essential for the broader industrial application of TiAl alloys. This study combines powder metallurgy and composite processes to develop a fine lamellar microstructure in high Nb-TiAl alloys, featuring a synergistic distribution of Si atoms and precipitated phases (TiB/Ti₅Si₃). The TiB phases serve as nucleation sites, promoting equiaxed γ grains at lamellar colony interfaces and refining the colony structure. This composite lamellar microstructure greatly improves strength and plasticity at both room and elevated temperatures. Notably, the 0.2SiB₆/TiAl-based composite exhibited a sixfold enhancement in room-temperature plasticity compared to the sintered high Nb-TiAl alloy, with ultimate tensile strength (UTS) rising from 608 MPa to 745 MPa. At 900 °C, the composites retained an outstanding UTS of 585 MPa, while the fracture strain was increased to 18.8%. These improvements are attributed to the refined lamellar colony, twin/twin intersections during plastic deformation, and the formation of stacking faults, all of which enhance work-hardening ability. Additionally, Si solid solution strengthening, precipitate phase strengthening, and their role in hindering dynamic recrystallization significantly improve high-temperature strength. This microstructural design offers a promising approach for developing TiAl-based composites possessing remarkable room and elevated-temperature properties.

Key words: TiAl alloys, Sintering, Composite materials, Microstructure design, Strength-ductility synergy