To eliminate the composition transient zone in directional solidification of TiAl alloys

The technique of directional solidification (DS) with cold-crucible and seeding is used to control the lamellar orientations in the solidified structures of TiAl alloys. However, the concentration transient zone (CTZ), a characteristic of alloy DS, may result in failure of the structure control because the CTZ separates the seed and the directionally solidified peritectic structure of TiAl alloys due to the β-phase formation. A composition adjusting method is proposed to eliminate the CTZ in this paper. Measurements were carried out to determine the macro-composition distributions in the directionally solidified Ti-Al%-Si% samples with and without the composition adjustment. The CTZ length measured in the directionally solidified sample without composition adjustment shows to be comparable to that predicted by a zone-melting-equivalent modeling performed in the present work. The experimental results for the CTZ control in zone-melting-like DS process with a cold crucible are exhibited. These results show that the CTZ control is feasible.