Surface tension of liquid Fe, Nb and 304L SS and effect of drop mass in aerodynamic levitation

The oscillating drop method has been widely used for surface tension measurements of liquids at high temperatures such as molten metals. An experimental device that permits such measurements has been developed at IRDL. This device relies on aerodynamic levitation for the sample to be contactless and on acoustic excitation to make it oscillate at its resonance frequency, which is related to the surface tension with Rayleigh’s equation. Beforehand, experimentally, a lateral gas jet blows and controls the rotation of the drop due to its unpredictable behavior. Moreover, the effect of drop mass, usually studied for electromagnetic levitation, remains unknown for aerodynamic levitation. To fill this knowledge gap, levitated drops of different masses were numerically modeled to observe the influence of gravity or additional oscillation modes. It resulted that for light mass drops, such as those used for our surface tension measurement, it is not significant. Finally, our results on iron, niobium, and 304L stainless steel have been compared with the literature. For pure metals, we observed a similar decreasing behavior versus temperature. For steel, results highlighted the impact of experimental parameters on the surface tension (length of experiments and composition of the atmosphere). These measurements thus provide original results that will be useful for the numerical modeling of innovative industrial processes such as additive manufacturing or welding.