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

Abstract

• Semi-solid forging is applied to the fabrication of TiAl alloys for the first time. • The semi-solid forged TiAl alloy forms a lamellar-network two-scale structure through non-equilibrium solidification. • The semi-solid forged Ti-43Al-9V-0.3Y alloy exhibits excellent elongation of 82% at 800℃. 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 α 2 /γ lamellar colony + outer β 0 /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(β 0 ) + 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 β 0 /γ phases and special α 2 /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 β 0 /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.

Topics & Concepts