Effect of cooling rate and Y element on the microstructure of rapidly solidified TiAl alloys

The influence of cooling rate and rare earth yttrium element on the microstructure of two rapidly solidified TiAl alloys with nominal compositions of Ti-46Al-2Cr-2Nb and Ti-46Al-2Cr-2Nb-1.0Y (at.%) prepared by melt spinning method was studied. The results show that rapid solidification refined and homogenized the microstructure of TiAl alloys, comparing to the conventionally cast mother alloy. A metastable supersaturated α2 phase was retained to low temperature. With increasing cooling rate, the microstructure is refined more and contains more supersaturated α2 phases. Y element promotes γ phase nucleation, leading to more γ phase with more Y addition, γ phase was found mainly located at the grain boundaries. Besides the main two phases, supersaturated α2 and γ, Y-enriched phase was also found in the 1.0 at.% Y containing alloy. The Y-enriched phase distributes as sphere morphology homogeneously in the matrix with a grain size of 20-130 nm. With increasing cooling rate, the amount of Y-enriched phase was decreased, indicating an increasing solubility of Y atom in TiAl alloys.