Abstract: Alloy Ni-44Ti-5Al-2Nb-1Mo (atomic fraction,%) is directionally solidified (DS) at a constant temperature (1 550 ℃) in a range of withdrawal rates (0.3,1.2,3.0,6.0,18.0 mm/min) by liquid metal cooling technology. An investigation of the microstructural characteristics indicates that the DS processes do not affect the phase composition, but they do change the phase morphology of the alloy. The phase composition of DS samples remains the same as that of the as-cast specimen, which is composed of NiTi (B2), Ti₂Ni and Nb-rich Ti₂Ni phases. After DS, [100] becomes the preferred orientation in the NiTi matrix. With the withdrawal rate increasing, orientation [100] is significantly enhanced, and the solid/liquid interface morphology changes from coarse dendrite to cellular dendrite. At the same time, both the primary dendrite arm of NiTi and the precipitates are greatly refined. The directional dendrites and tiny precipitation distribution will be beneficial to the high temperature strength and room temperature ductility of the alloy.

Key words: intermetallic compound, alloy NiTiAl, directional solidification, microstructure, withdrawal rate