Suppression of Dynamic Nucleation by an Inert Atmosphere in Zr-2.5Nb-0.11O in ISS-EML

During electromagnetic levitation experiments, the electromagnetic field induces fluid flow within the molten sample. Materials with high melting temperatures, like zirconium and some of its alloys, rapid stirring can be sustained while the molten sample is undercooled. In these conditions, dynamic nucleation has been consistently and repeatably demonstrated in several zirconium and zirconium alloy samples in the Electromagnetic Levitator onboard the International Space Station (ISS-EML). Strong stirring was induced in molten zirconium with 2.5 at% niobium during electromagnetic levitation in an argon atmosphere at 350 mbar. The sample was observed at various sub-critical isothermal holds where dynamic nucleation has previously been observed during experiments in high vacuum. The sample remained liquid though the entire experimental timeframe. This behavior is consistent with the dynamic nucleation theory, which predicts that the frequency of nucleation should change in response to factors that suppress the excitation of voids in the melt, like external pressure.