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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 alloys, which corresponds to the maximum solid solubility of nickel phase, the solidification microstructure is characterized by nickel dendrite plus (Ni + NiMo) eutectic strucure. The undercooling of this alloy up to 182 K has been realized in the experiments. With an in-crease in under cooling, The microstructural evolution of primary Ni phase in Ni-45% Mo hypoeutectic alloy evolves from remelted dendrite to equiaxed grains, while Ni-47.7% Mo eutectic alloy exhibits a structural transition from lamellar eutectic to anomalous eutectic. Theoretical analyzes 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.