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 Y2O3-coated Al2O3 (Y2O3/Al2O3) crucibles and conventional Al2O3 crucibles with a withdrawal rate of 1 x 10(-4) m s(-1) at 1550, 1650, and 1750 A degrees 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)(4)Ni2O 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 A degrees 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 A degrees C contained a small amount of Y2O3 particles, its maximum oxygen increase was only 0.046 wt%.