Interactions between Ni-44Ti-5Al-2Nb-Mo alloy and oxide ceramics during directional solidification process

Interactions between Ni-44Ti-5Al-2Nb-Mo (at.%) alloy and oxide ceramics during the directional solidification (DS) process were studied. The experiments were performed using novel Y ₂O ₃-coated Al ₂O ₃ (Y ₂O ₃/Al ₂O ₃) crucibles and conventional Al ₂O ₃ crucibles with a withdrawal rate of 1 9 10-4 m s-1 at 1550, 1650, and 1750 °C, respectively. The results indicated that the Al ₂O ₃ reacted with the NiTi-Al alloy strongly, leading to the formation of the TiO and (Ti,Al) ₄Ni ₂O inclusions. The extent of the reaction increased with increasing heating temperature at a constant withdrawal rate. The oxygen increase in directionally solidified ingot using the Al ₂O ₃ crucible was up to 1.366 wt% at 1750 °C. With the same DS parameters using the Y ₂O ₃/Al ₂O ₃ crucible, no chemical reaction occurred between the Y ₂O ₃ and the alloy, suggesting that the Y ₂O ₃ layer exhibited an effective barrier capability to avoid the reaction between the Al ₂O ₃ and NiTi-Al alloy. Although the alloy ingot obtained at 1750 °C contained a small amount of Y ₂O ₃ particles, its maximum oxygen increase was only 0.046 wt%.