Heterogeneous nucleation and dendritic growth within undercooled liquid niobium under electrostatic levitation condition

The physical mechanisms of crystal nucleation and dendritic growth within undercooled niobium were systematically studied by electrostatic levitation and molecular dynamics methods. The maximum undercooling was achieved as 454 K (0.16T_m), while the hypercooling limit was determined as 706 K (0.26T_m). The undercooling probability displayed Poisson distribution and indicated the occurrence of heterogeneous nucleation. The calculated critical nucleus size reduced rapidly with undercooling and the solid-liquid interface energy was deduced to be 0.367 J m⁻². In addition, the dendritic growth velocity of pure niobium exhibited a power relation versus undercooling, and reached 41 m s⁻¹ at the maximum undercooling.