定向凝固Ni-44Ti-5Al-2Nb-1Mo合金的组织特征

采用液态金属冷却定向凝固方法制备了Ni-44Ti-5 Al-2 Nb-1 Mo(原子分数,％)合金,分析了加热温度为1 550℃,抽拉速率为0.3、1.2、3.0、6.0、18.0 mm/min时的定向凝固组织特征.结果表明,定向凝固没有改变合金的相组成,但改变了组成相的形态.定向凝固组织均由初生的NiTi相与晶间析出...

Microstructural Characteristics of Directionally Solidified Alloys Ni-44Ti-5Al-2Nb-1Mo

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.