Microstructure of Rapidly Solidified Ti-46Al-2Cr-2Nb-xY Alloys

In this paper, a rapid solidification (RS) method was employed to produce yttrium-containing TiAl based alloy ribbons. The microstructure evolution was investigated in terms of yttrium addition and RS parameters. For comparison, the conventionally cast counterpart alloys were studied as well. It was found that the microstructure of as cast alloys is sensitive to the Y content. The alloys with addition of 0 to 1.0at.% Y were of lamellar microstructures, but the alloy samples with 1.5 and 2.0at.% Y additioin were of strip-like microstructure. The yttrium-free alloy exhibited full γ phase, while the Y-bearing alloys contain γ phase, a small amount of α2, and yttrium containing phases. With increasing Y content, the secondary dendritic arm spacing (SDAS) gradually reduced. In the case of the rapidly solidified alloys, the microstructure was refined evidently when compared with the as cast counterparts. The fine Y-rich precipitates were homogeneously distributed in the matrix with a particle size of several tens of nanometers. A bcc phase (a=0.314 nm) was found in the alloys containing more than 1.5at.% Y, which was attributed to the extension of the solubility of Y in the matrix by rapid solidification.