Directional Solidification Microstructure of Ti-46Al-8Nb Alloy and Effectof Crystal Selector Angle on Alloy Lamellar Orientation

Ti-46Al-8Nb (atomic fraction/%) alloy was directionally solidified by using BaZrO₃/Al₂O₃ composite mold shell with Bridgman furnace. The interface erosion layer morphology, microstructure and phase composition of the alloy, and the effect of the crystal selector angle on the crystal selection efficiency and the alloy lamellar orientation were studied. The results show that after directional solidification, a 10 μm thick erosion layer existed at the bottom of the alloy. With increasing height, the oxygen content in the alloy and the thickness of the erosion layer increased. The alloy had a full lamellar structure composed of γ (TiAl) and α₂ (Ti₃Al) phases, and no inclusions existed. Within 30°-60°, the smaller the crystal selector angle was, the higher the crystal selection efficiency was. The crystal selector angle had little effect on the angle between the alloy lamellar orientation and growth direction.