Mechanism of α→α2+γ phase separation in hypo-eutectoid Ti-37 at%Al alloy

Features of the alpha-->alpha(2)+gamma phase separation in a hypo-eutectoid Ti-37 at%Al alloy were investigated by transmission electron microscopy. Note that the eutectoid reaction in the Ti-Al alloy system takes place at 1398 K in an Al concentration of 40 at%. The present data clearly show that in the hypo-eutectoid alloy the alpha(2)+gamma lamellar structure is formed in an equilibrium state, just as in cases of the eutectoid and hyper-eutectoid alloys. A characteristic feature in the hypo-eutectoid alloy is the appearance of the amorphous state as an intermediate stale. In other words, the sequence of the formation of the lamellar structure is the same as that in the eutectoid alloy, not in the hyper-eutectoid alloy. It can be therefore concluded that there are two types of the processes for the lamellar-structure formation in the phase separations of the Ti-Al alloy system.