High-performing TiAl alloy with lamellar-network two-scale structure via semi-solid forging and its non-equilibrium solidification mechanism

TiAl alloys are lightweight, high-strength, and have good mechanical properties at elevated temperatures, rendering them appealing for high-temperature applications. However, their difficult processing, and limited ductility at ambient temperatures have hindered their widespread application. Here, we report fabrication of a Ti-43Al-9 V-0.3Y alloy with a novel lamellar-network two-scale structure comprising an inner α₂/γ lamellar colony + outer β₀/γ phases via semi-solid forging process. The formation of this lamellar-network two-scale structure is elucidated from the perspective of the solute diffusion and redistribution occurring, and occurs due to liquid segregation and a non-equilibrium transition of L → β(β₀) + α at late solidification. Compared to the as-cast alloy, the semi-solid forged alloy exhibits significant increases in elongation and tensile strength at room temperature and 800°C. The high density of dislocations and mechanical twins in the β₀/γ phases and special α₂/γ lamellae during tensile deformation effectively release the plastic deformation potential of the TiAl alloy at room temperature. Moreover, the abundant nano-twins in the β₀/γ phase and γ dynamic recrystallization behavior at 800 ℃ significantly enhance the high-temperature plasticity. This approach and microstructure offer a promising solution to the engineering challenges posed by the low room-temperature ductility and limited hot-working ability of TiAl alloys.