Time development of a perturbed-spherical nucleus in a pure supercooled liquid. II. Nonlinear development

The nonlinear stage of free growth of a spherical solid nucleus from a pure supercooled liquid has been studied numerically in a fully time-dependent context. The emergence of a dominant mode from arbitrary initial conditions, including random perturbations, is found to correspond to the most unstable mode determined from linear stability analysis. The growth of instabilities, initiated by localized defects analogous to point and line defects in crystal lattices, is analyzed, and it is shown that the perturbations grow and spread in a wavelike manner, a phenomenon observed in experiments. The formation of a predendritic growth stage is characterized by establishment of constant values of tip radius and velocity.