Interactions between TiAl Alloy and Different Oxide Moulds under High-temperature and Long-time Condition

Interactions between Ti-47Al-2Cr-2Nb (at.%) alloy and alumina, zirconia and yttria moulds were studied under high-temperature and long-time condition, and the reaction mechanisms were explored. The moulds were prepared by traditional precision casting technique, and the experiments were carried out in a carbon resistance furnace at 1550 degrees C for 30 min. The results indicated that the interfacial reactions between TiAl alloys and alumina and zirconia moulds were serious. Obvious reaction layers composed of Ti-rich phases and Al2O3 inclusions were formed on the alloy-mould interfaces, and a large amount of dark Al2O3 inclusions were found in the alloy matrixes. Interaction between TiAl and yttria mould was mild. No obvious reaction layer was formed on the alloy-mould interface, and only a small amount of white inclusions inferred as Al-Y oxide were found in the alloy matrix. Al2O3 and ZrO2 cannot be used as mould materials for the directional solidification of TiAl alloys. Y2O3 mould possesses a higher stability, which can be used in the directional solidification of TiAl alloys by the proper choice of more stable binder.