Three-dimensional analysis and morphological characterization of coarsened dendritic microstructures

The dendritic microstructures of isothermally coarsened Pb-Sn samples are examined for various coarsening times and three different volume fractions. A total of sixteen directionally solidified samples are studied for coarsening times ranging from 3 minutes to 4 days for 43%, 58% and 81% volume fraction of solid.; Morphological analysis is initially achieved through three-dimensional reconstructions of the microstructures, which allow for the observation of morphological features not attainable in two-dimensions. The length scale of each microstructure is measured with the inverse surface area per unit volume, S-1v A linear increase of the length scale with the cube root of coarsening time is observed for the samples of all three volume fractions, although the systems clearly do not evolve in a self-similar fashion.; Quantitative morphological characterization is achieved through interfacial shape distributions (ISDs), which measure the probability of having an interfacial patch within a given range of principal interfacial curvatures. Specific microstructural location (SML) figures emphasize specific parts of the microstructure corresponding to selected areas of the ISD, allowing for more insight into the various interfacial shapes.; In order to investigate any symmetry or preferential directionality in the microstructures, the interfacial normal distributions (INDs) are used, which measure the probability of having an interfacial patch with a specific spatial orientation. Strong two-fold symmetry is observed for the late coarsening times of the 43% and 58% volume fraction samples, whereas four-fold symmetry is seen for the earliest coarsening time of the 81% volume fraction sample.; A common feature of the various microstructures is the presence of cylindrical inter-facial shapes for late coarsening times. Solid cylinders form in the 43% and 58% volume fraction samples when the mean curvature of the main dendritic stems becomes comparable to that of the surrounding interfaces. Liquid cylinders form in the 81% volume fraction samples. Liquid walls, a dominant feature of these samples, are responsible for the formation of the liquid cylinders. Lack of spherodization of solid or liquid cylinders is also observed. The growth rate of the perturbations is approximately the same or even slower than the ripening rate and spherodization does not occur.