Replacing eutectic growth by glass formation for liquid Ni_59.5Nb_40.5 alloy under containerless state

The eutectic growth kinetics and glass forming ability of undercooled liquid Ni_59.5Nb_40.5 alloy were investigated by containerless processing via electromagnetic levitation (EML) and drop tube (DT) techniques. The maximum liquid undercoolings attained 120 K (0.08 T_E) at levitated state and 564 K (0.38 T_E) under free fall condition respectively. As liquid undercooling increased, three distinctive undercooling regimes were determined experimentally. At low undercoolings, normal lamellar eutectic growth occurred, with a eutectic growth velocity of 27 mm s⁻¹ at 120 K undercooling under EML condition. In the intermediate undercooling range between 184 and 380 K, Nb₇Ni₆ phase could nucleate primarily and independently, which resulted in a typical hypereutectic microstructure. Once undercooling exceeded 380 K, both eutectic growth and Nb₇Ni₆ dendrite growth were suppressed, leading to the formation of amorphous phase. Molecular dynamics simulation revealed that alloy viscosity increased significantly with liquid undercooling, which contributed to the reduced nucleation rate and suppressed crystal growth.