The dendritic microstructure that develops during solidification of metallic alloys plays a significant role in defining the characteristics of the material. The shape of dendrite tips directly influences the overall dendritic pattern, but in situ characterization of dendrite tips in bulk systems during directional solidification is rare because of experimental complexity. Here, we quantitatively characterize the three-dimensional (3D) tip shapes of dendrites grown during directional solidification of a transparent succinonitrile–0.46 wt% camphor alloy in the microgravity environment of the International Space Station, where convection is suppressed. The 3D reconstruction of the shape of dendrite tips is obtained through the analysis of interferometry images. Results are compared with both sharp-interface theory and 3D phase-field simulations. The experimental results are found to be in reasonably good quantitative agreement with the predictions of microscopic solvability theory and phase-field simulations despite a wider-than-expected scatter in measured tip radii that could be because of measurement uncertainties and other factors.

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• Growth
• Microstructure
• Alloys
• Phase-field modeling
• Solidification