Quantitative analysis of facet growth during directional solidification of salol.

Abstract

The growth dynamics of faceted materials exhibit slow attachment kinetics, strong solid-liquid anisotropy, and specific kinetic coefficients. The formation of structures, facet dynamics and defects during growth strongly influence the properties of the resulting materials. Using the transparent model material salol and the method of controlled directional solidification, this work aims to provide a deeper understanding of the formation of structures in faceted materials, which remain insufficiently understood. The study reveals that after an initial transient period, the solid-liquid interface stabilizes, with its position linked to the interface undercooling. Facet size heterogeneity is characterized with a tendency to larger facets for lower thermal gradients. A methodology is developed to exploit experimentally measured angles into a three-dimensional angle in the crystals, allowing the identification of the crystallographic nature of the facets. Despite random and unknown initial orientations, the interface is predominantly bounded by {111} planes. Facet velocities are analyzed, and deviations from theoretical predictions are attributed to competitive growth processes. The analysis of facet velocities as a function of undercooling suggests a growth mechanism primarily controlled by two-dimensional nucleation. It is shown that the experimental data relating the growth rate of {111} facets to the undercooling correspond to bi-dimensional kinetic growth law in most cases. Only a few data point can be related to a kinetic growth law driven by screw dislocation emerging at the {111} facet surface.