Sub-second Surface Tension Measurement of Steels Containing Manganese in Aerodynamic Levitation

Abstract

Surface tension of metals is a data of interest for the simulation of welding or additive manufacturing. In this regard, surface tension of three steels has been measured with an experimental device of aerodynamic levitation with the well-known oscillating drop method (observation of the resonance frequency of the drop). Steel can be very sensitive to evaporation that occurs above melting point which can lead to the modification of the chemical composition and thus of the thermophysical properties. One option to limit evaporation is to reduce the duration of the experiment. In this perspective, a new acoustic method has been tested, which consists in exciting the sample with a frequency close to the resonance frequency for a fraction of second and then observing the frequency naturally adopted by the drop during a short relaxation time. This reduces the time of the experiment to less than 1 s, against about 10 s with the frequency sweep method previously used. Both methods are used and discussed in this article. The solicitation-relaxation method is found to significantly reduce the evaporation and thus provides more consistent results at high temperatures. For the steel on which this new method has been tested, the characteristic increasing–decreasing surface tension with temperature has been observed, which can have an impact on the melt pool dynamic in welding or additive manufacturing and should be considered in numerical simulation for better results.