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

The high strength and stability of the full-lamellar structure guarantee the industrial application of the beta-solidifying gamma-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 beta and alpha single-phase region during the solidification. It is found that the full-lamellar structure can be obtained by the solution heat treatment at 1230 degrees C for 20 min and then aging treatment at 800 degrees C for 3 h. Interestingly, a new microstructure, namely, the pearlitic-like microstructure (PM) induced by the alpha(2)/gamma -> beta(o) + gamma cellular reaction was observed when the aging temperature is increased to above 800 degrees 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 degrees C, respectively. The mechanism of the reduced alpha(2)/gamma lamellae and PM formation was discussed regarding the heterogeneous distribution of beta stabilizing elements and the interface energy stored in alpha(2)/gamma lamellae.