中文摘要：

采用真空电弧熔炼水冷铜模吸铸法制备Ni-50%Sc合金（摩尔分数,下同）,采用程序计算、光学和扫描电子显微镜分析B2-NiSc金属间化合物急冷快速凝固组织的演化规律,采用XRD和EDS分析合金组织的相组成。结果表明：以名义成分Ni-50%Sc配制合金,真空水冷铜模吸铸成d 2、d 5和d 8 mm急冷试样对应的凝固速率分别为3112、497.9和194.5 K/s。Ro=1.5 mm为临界尺寸,对应着凝固速率的骤然变化。因Sc含量的损失,枝晶间出现了共晶（Ni2Sc＋NiSc）组织;R〉Ro（d5和d 8 mm试样）,凝固组织为粗大枝晶B2-NiSc＋共晶（Ni2Sc＋NiSc）组织;

英文摘要：

Ni-50%Sc alloy was prepared with a vacuum arc smelting and water cooled copper mold suction-casting machine. The microstructure evolution of the rapidly solidified alloy which mainly consists of B2-NiSc phase was analyzed by optical metalloscopy and scanning electron microscopy. The microstructure constitutes was also calculated with an Image-Pro Plus software. XRD was used to identify phase microstructural components, and further more the composition of each phase was analyzed with EDS. The cooling rates for the solidified specimens with diameters of 2, 5 and 8 mm were 3112, 497.9 and 194.5 K/s, respectively. It is found that Ro=3/2 mm is a critical dimension which corresponds to an abrupt change in solidification rate. It is also found that eutectic mixture structure of（Ni2Sc＋NiSc） is dispersed at grain boundary or between dendritic arms due to the loss of Sc element during melting. While RRo（corresponding to the specimens with diameters of 5 and 8 mm）, the solidification structure consists with coarse B2-NiSc dendrite and eutectic（Ni2Sc＋NiSc）. While RRo（corresponding to the specimens with diameter of 2 mm）, the solidification structure consists with fine globular B2-NiSc dendrite and relatively small amounts of eutectic（Ni_2Sc＋NiSc）. Based on the phase volumetric analyzing of the microstructure with an Image-Pro Plus software, the loss of Sc element during melting is about 3.25%~3.31% in according with specimens diameters. Therefore, it could be concluded that B2-NiSc intermetallics without any second phase is difficult to achieve under the condition of sub-rapid solidification. Microstructures underwent（970 ℃, 72 h） homogenization heat treatment of the rapid solidified specimens were analyzed. Spherical Ni2Sc particles are dispersed on the B2-NiSc matrix for the specimen with 2 mm diameter, but the second phase Ni2Sc is in plate shape for the specimens with 5 and 8 mm diameters.