(北京航空航天大学 材料科学与工程学院，北京 100191)
摘 要: 采用Bridgman型液态金属冷却定向凝固方法，研究Ni-45Ti-5Al(摩尔分数，%)合金在不同抽拉速率(20、100和200 μm/s)下定向凝固后的相组成及其形态特征。结果表明：Ni-45Ti-5Al合金定向凝固生长区呈现明显的柱状晶生长形态，定向效果良好，NiTi基体以[100]方向为择优取向，Ti2Ni析出相沿[111]晶向择优生长。随着抽拉速率的提高，Ti2Ni相更加细小、分散，由在胞晶界上几乎连续分布改变为断续分布。在20~200 μm/s的宽生长速率范围内，均以胞状晶形态生长，固/液界面形态没有发生显著变化；随着抽拉速率从20 μm/s增加到200 μm/s，定向胞晶组织明显细化，平均胞晶间距由85 μm减小到25 μm。
关键字: Ni-45Ti-5Al合金；定向凝固；微观组织；固/液界面
directionally solidified Ni-45Ti-5Al alloys
（School of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100191, China）
Abstract:The phase compositions and shapes of directionally solidified (DS) Ni-45Ti-5Al (mole fraction, %) alloys were investigated in the Bridgman liquid-metal-cooling directional-solidification process at withdrawal rates of 20, 100 and 200 μm/s. The results show that the columnar grain growth is observed in the DS specimens. The preferred crystal orientation of NiTi matrix is [100] direction and that of Ti2Ni phase precipitated on the matrix is [111] direction. With the increase of withdrawal rate, the Ti2Ni phase becomes finer and distributes from continuously to discontinuously in the intercellular region. When the withdrawal rate varies from 20 μm/s to 200 μm/s, all the solid/liquid interface morphologies are cellular, the DS microstructure is refined obviously and the cellular spacing decreases from 85 μm to 25 μm.
Key words: Ni-45Ti-5Al alloy; directional solidification; microstructure; solid/liquid interface
