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The TiAl-based alloy has excellent high-temperature comprehensive properties such as low density, high specific strength and high specific stiffness. It is expected to replace a nickel-based alloy with high density in aero-engine manufacturing. In this paper, the transformation rule of β₂-phase and its effect on the mechanical properties at room temperature in the cast TiAl alloy were studied systematically. The experimental results demonstrated that the toughness of the cast Ti-Al-Nb-Cr-Mo-B alloy is not decreased when the holding time is 2h, but the strength increased from 1200MPa to 1500 MPa. In the process of heat preservation, α decomposes into γ + β phase, and then in the process of cooling, the disordered β phase transforms into ordered β₂ phase. The experimental results show thatβ₂ phase is a hard brittle phase, and a small amount of β₂ phase can promote the strength of the alloy.