Rapid growth of nickel dendrite in highly undercooled Ni-Mo alloys  

作　　者：姚文静 魏炳波 

机构地区：[1]Laboratory of Materials Science in Space,Department of Applied Physics,Northwestern Polytechnical University,Xi'an 710072,China

出　　处：《Science China(Technological Sciences)》2003年第6期593-606,共14页中国科学（技术科学英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.50221101,50291015 and 50271058);Huo Yingdong Education Foundation(Grant No.71044);the Doctorate Foundation of Northwestern Polytechnical University(Grant No.200243)

摘　　要：Ni-39.3%Mo, Ni-45%Mo hypoeutectic alloys and Ni-47.7%Mo eutectic alloy have been rapidly solidified with different droplet sizes by containerless processing in a drop tube. For Ni-39.3%Mo hypoeutectic alloy, which corresponds to the maximum solid solubility of nickel phase, the solidification microstructure is characterized by nickel dendrite plus (Ni+NiMo) eutectic struc-ture. The undercooling of this alloy up to 182 K has been realized in the experiments. With an in-crease in undercooling, the dendritic microstructure is refined. The microstructural evolution of primary Ni phase in Ni-45%Mo hypoeutectic alloy evolves from remelted dendrite to equiaxed grains, whereas Ni-47.7%Mo eutectic alloy exhibits a structural transition from lamellar eutectic to anomalous eutectic. Theoretical analyses indicate that, for Ni-39.3%Mo, Ni-45%Mo and Ni-47.7%Mo alloys, the nickel phase shows a transition from solutal-diffusion-controlled growth to thermal-diffusion-controlled growth at undercoolings of 66.6, 81.9 and 85.0 K. The critical transition temperature decreases with a reduction in the nickel content.Ni-39.3%Mo, Ni-45%Mo hypoeutectic alloys and Ni-47.7%Mo eutectic alloy have been rapidly solidified with different droplet sizes by containerless processing in a drop tube. For Ni-39.3%Mo hypoeutectic alloy, which corresponds to the maximum solid solubility of nickel phase, the solidification microstructure is characterized by nickel dendrite plus (Ni+NiMo) eutectic structure. The undercooling of this alloy up to 182 K has been realized in the experiments. With an increase in undercooling, the dendritic microstructure is refined. The microstructural evolution of primary Ni phase in Ni-45%Mo hypoeutectic alloy evolves from remelted dendrite to equiaxed grains, whereas Ni-47.7%Mo eutectic alloy exhibits a structural transition from lamellar eutectic to anomalous eutectic. Theoretical analyses indicate that, for Ni-39.3%Mo, Ni-45%Mo and Ni-47.7%Mo alloys, the nickel phase shows a transition from solutal-diffusion-controlled growth to thermal-diffusion-controlled growth at undercoolings of 66.6, 81.9 and 85.0 K. The critical transition temperature decreases with a reduction in the nickel content.

关 键 词：DENDRITE rapid growth drop tube UNDERCOOLING NI-MO 

分 类 号：TG13[一般工业技术—材料科学与工程]