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

Abstract

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 Y₂O₃-coated Al₂O₃ (Y₂O₃/Al₂O₃) crucibles and conventional Al₂O₃ crucibles with a withdrawal rate of 1 × 10⁻⁴ m s⁻¹ at 1550, 1650, and 1750 °C, respectively. The results indicated that the Al₂O₃ reacted with the NiTi-Al alloy strongly, leading to the formation of the TiO and (Ti,Al)₄Ni₂O 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 Al₂O₃ crucible was up to 1.366 wt% at 1750 °C. With the same DS parameters using the Y₂O₃/Al₂O₃ crucible, no chemical reaction occurred between the Y₂O₃ and the alloy, suggesting that the Y₂O₃ layer exhibited an effective barrier capability to avoid the reaction between the Al₂O₃ and NiTi-Al alloy. Although the alloy ingot obtained at 1750 °C contained a small amount of Y₂O₃ particles, its maximum oxygen increase was only 0.046 wt%.