Influence of heat treatment on microstructure of a new β-solidifying γ-TiAl alloy

The high strength and stability of the full-lamellar structure guarantee the industrial application of the β-solidifying γ-TiAl alloys. However, it is a huge challenge to design an alloy with good hot-deformability as well as the full-lamellar structure. The low-cost Ti–42.5Al–2Mn–0.4Mo–0.1B–0.1C (at.%) alloy was designed, which undergoes both β and α single-phase region during the solidification. It is found that the full-lamellar structure can be obtained by the solution heat treatment at 1230 °C for 20 min and then aging treatment at 800 °C for 3 h. Interestingly, a new microstructure, namely, the pearlitic-like microstructure (PM) induced by the α₂/γ → β_o + γ cellular reaction was observed when the aging temperature is increased to above 800 °C. The volume fraction of the PM is gradually increased from 0% to 25.5%, 65%, and 94% according to elevated aging temperature from 800 to 900, 1000, and 1050 °C, respectively. The mechanism of the reduced α₂/γ lamellae and PM formation was discussed regarding the heterogeneous distribution of β stabilizing elements and the interface energy stored in α₂/γ lamellae.