Interface reaction between ceramic moulds and high Nb-TiAl alloys

The interface reaction between Ti-44Al-8Nb-0.2W-0.1B-0.1Y (at%) alloy and Al₂O₃/ZrO₂/ Y₂O₃ crucibles was investigated. The thicknesses of the interface reaction layers are about 40, 170 and 20 μm. The most interesting is the microstructure transformation of Ti-44Al-8Nb-0.2W-0.1B-0.1Y solidifying in different crucibles. After solidifying in Al₂O₃/ZrO₂/ Y₂O₃ crucibles, the oxygen contents in Ti-44Al-8Nb-0.2W-0.1B-0.1Y alloy are measured to be 0.35, 0.41 and 0.11 (at%). During melting and solidification, oxygen in crucibles will diffuse into the alloy matrix. High oxygen content causes microstructure transformation. Peritectic reaction occurs in the alloys solidifying in Al₂O₃ and ZrO₂ crucibles. For contrast, Ti-49.5Al-2Cr-2Nb alloy was chosen to make investigation. No visible microstructure difference is found in alloys solidified in various crucibles though the oxygen contents are determined as 0.40, 0.63 and 0.25 (at%).