Space microgravity enhanced fractal dendrite coverage on solidifying alloy droplet surface

Under terrestrial gravity, alloy solidification is significantly influenced by temperature gradients, intense natural convection, and non-uniform solute redistribution, often leading to preferential dendritic growth and reduced structural symmetry. This article investigates dendritic growth in levitated Ti47.5Ni47.5V5 alloy droplets under microgravity, where buoyancy-driven convection is strongly suppressed, and Marangoni convection becomes the dominant flow mechanism. With the Marangoni number of Ma ≈ 4, the velocity ratio between dendritic growth and liquid flow of vd/vL ∼ 104 indicates that the solidification front propagates much faster than the interfacial flow. Therefore, dendritic growth is primarily governed by diffusion, resulting in nearly isotropic branching and highly symmetrical microstructures. Increased undercooling further enhances the fractal dimension and spatial filling efficiency through its effect on dendritic growth kinetics. The findings provide quantitative implications of weak Marangoni transport and rapid interfacial instability during phase change and establish a benchmark for understanding how Marangoni convection perturbs interfacial dynamics in rapid solidification systems under microgravity.