MECHANISM OF ALPHA-]ALPHA(2)-SEPARATION IN HYPO-EUTECTOID TI-37 AT-PERCENT-AL ALLOY(GAMMA PHASE)

Features of the alpha-->alpha(2)+gamma phase separation in a hypo-eute ctoid Ti-37 at%Al alloy were investigated by transmission electron mic roscopy. Note that the eutectoid reaction in the Ti-Al alloy system ta kes 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 lame llar 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 a n intermediate stale. In other words, the sequence of the formation of the lamellar structure is the same as that in the eutectoid alloy, no t in the hyper-eutectoid alloy. It can be therefore concluded that the re are two types of the processes for the lamellar-structure formation in the phase separations of the Ti-Al alloy system.