Containerless Liquid Flow Modulated Surface Dendritic Growth of Refractory Alloys Under Space Microgravity and Terrestrial Gravity

It is well-established that fluid flow exerts a significant influence on dendritic growth morphology. Under terrestrial gravity, the impact of natural convection within opaque alloy melts on dendritic dynamics is challenging to observe directly. We therefore employed electrostatic levitation platform aboard the China Space Station to specifically investigate surface dendritic growth morphology under both microgravity and terrestrial gravity. After containerless experiments in outer space, highly symmetric and well-developed dendrites were observed on the surface of alloy spheres. This stands in distinctive contrast to the fragmented dendrites found on alloy surface from ground-based containerless experiments. To further elucidate the differences of surface dendritic morphology between microgravity and gravity, we simulated the rapid solidification process from an undercooled state by an extended theoretical model. The result explains how fluid flow modulated surface dendritic growth under both gravity and microgravity: during the onset of surface dendritic growth, the global flow velocity under microgravity was markedly lower than that under gravity, accompanied by a significantly larger expanse of weak-flow zones—regions where local flow velocity falls below the dendritic growth velocity. This study offers further insights for developing high-temperature materials under both space microgravity and terrestrial gravity.