Complete solute trapping of rapidly growing nickel dendrites within liquid Ni₇₂Mo₂₈ hypoeutectic alloy

The rapid dendrite growth in highly undercooled liquid Ni₇₂Mo₂₈ hypoeutectic alloy was accomplished by containerless processing via electromagnetic levitation and drop tube techniques. The (Ni) dendrites achieved a high growth velocity of 26 m/s at the maximum undercooling of 226 K (0.14 T_L) under levitated state. Remarkable dendritic structure refinement and Mo solubility extension were observed with the increase in undercooling. For freely falling alloy droplets, the largest undercooling was enhanced to 246 K (0.15 T_L), which resulted in thorough solute trapping and almost segregationless solidification. A microstructure transition from columnar dendrite to equiaxed dendrite took place once alloy undercooling exceeded a threshold about 74-79 K. In addition, the Vickers hardness of primary (Ni) dendrite was significantly improved, which was caused by the extension of Mo solubility and microstructure refinement.