Pii: S1359-6454(99)00115-9

ÐThe sidebranching behavior in free dendritic growth into a supercooled melt is investigated through a detailed measurement of the sidebranch structure of succinonitrile (SCN) dendrites using images from the microgravity experiment of Glicksman and co-workers. The measurements show that the sidebranching evolution is divided into two regimes: an initial linear regime and a subsequent non-linear coarsening regime. A simple model, based on the Mullins±Sekerka linear stability theory, is developed to describe the initial sidebranching behavior. The excellent agreement of the model prediction with the experimental results indicates that the initial sidebranch spacings are selected by the maximum instability wavelength. In the non-linear regime, two new geometrical parameters, derived from the measurements, are proposed to characterize the coarsening process of the sidebranches and to compare the measurements with available coarsening theories. It is found that coarsening at the sidebranch roots follows closely classical laws for purely capillary-driven isothermal coarsening, but the overall coarsening process of the entire sidebranching dendrite cannot be explained by these isothermal coarsening theories. # 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.