Microstructure evolution in rapidly solidified y added TiAl ribbons

In the present study, Ti-46Al-2Cr-2Nb (atomic ratio) based alloys with various yttrium additions (0, 0.5, 1.0, 1.5, 2.0 at.%) have been produced by melt spinning method and the microstructure evolution with Y additions was studied intensively. For comparison, cast alloys with the same compositions were also prepared by argon arc melting. Investigations revealed that Y additions have an evident influence on the microstructure of the both alloys. With the addition of up to 1.5 at.% Y, the microstructure of the as-cast alloys changed from lamellar, typical of the Y free alloy, to dendritic, while the addition of 2 at.% Y led to a finer dendritic structure than for the 1.5 at.% Y alloy. For the rapidly solidified TiAl based alloys, a considerably refined microstructure was produced. Increasing Y concentration progressively modified the phase constituents from γ-TiAl + α₂-Ti₃Al phase, to γ-TiAl + α₂-Ti₃Al + a small fraction of Al₂Y phase, and then to γ-TiAl + α₂-Ti ₃Al + a small fraction of Al₂Y + B2 phase. Although the phase constitutions on the roll contact and free surfaces of the rapidly solidified ribbons were essentially the same, the microstructure of the former was finer than that of the latter.