Active Eutectoid Decomposition of α → γ + τ1 and the Morphological Evolution in a Ru-Containing TiAl Alloy

The active eutectoid decomposition and its morphological evolution during slow cooling and isothermal holding were investigated in a Ru-containing TiAl alloy. The fine τ1/γ active eutectoid nodules precipitated at α grain boundary and interior during water quenching. The active eutectoid microstructure evolved from sheaf-like, granular to bulky net-like sluggish eutectoid morphology gradually with the decrease in quenching/holding temperatures. The active eutectoid reaction occurs from 1220 to 1290 °C, while the beginning temperature of sluggish eutectoid locates at 1305 ± 5 °C. The combination of the intact τ1 phase and immature nano-sized γ laths suggests a short incubation period of τ1 phase in the active type. Furtherly, the semiquantitative estimation shows that the growth velocity of active eutectoid is about ninety times higher than sluggish type. In addition, a representative feature of γ phase abruptly ripening along {111} crystallographic plane was also observed in the active eutectoid.