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°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 Al ₂O₃ 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. Y₂O ₃ mould possesses a higher stability, which can be used in the directional solidification of TiAl alloys by the proper choice of more stable binder.