Growth, structure, and morphological stability of nuclei growing from eutectic melts

Abstract

Kinetics of self-consistent growth of new-phase nuclei from eutectic melts have been studied. The growth kinetics of nuclei of eutectic composition are shown to depend on the sum of supersaturations over all components. It has been established that nuclei in a eutectic melt reach a common critical radius determined by supersaturation for both components. The concept of a diffusion dipole is introduced: a two-phase object in a eutectic melt or solid solution, in which two nuclei of different composition are related through a common diffusion field. The morphological stability of such dipoles is studied. It is found that a nucleus of eutectic composition is more stable with respect to small fluctuations in its shape than the corresponding one-component nucleus. It is shown that perturbations resulting in dipole-shape distortions develop perpendicular to the axis connecting the centers of the nuclei of different compositions (i.e. the dipole axis). This is consistent with the well-known experimental observation of the layered structure of eutectic compositions.