S. Reutzel

Change of the kinetics of solidification and microstructure formation induced by convection in the Ni–Al system

The purpose of the present work was to measure the velocity of dendrite growth in undercooled Ni–Al alloy melts as a function of undercooling. The experiments were performed both by containerless electromagnetic levitation on Earth and under reduced gravity conditions during parabolic flight campaigns. While under terrestrial conditions, strong magnetic fields are required to compensate the gravitational force, the forces to compensate disturbing accelerations are decreased by orders of magnitude in reduced gravity. In turn, the alternating electromagnetic fields induce convection, which is strong under terrestrial conditions while much weaker in reduced gravity. The heat and mass transport in front of the solid-liquid interface during solidification controls the dynamics of dendrite growth. By comparing results obtained on Earth and in reduced gravity, it was demonstrated that the change of transport conditions by convection significantly alters the kinetics of solidification and the evolution of grain r...

Measuring Magnetic Susceptibility of undercooled Co-based alloys with a Faraday Balance

Co-based melts embedded by glass flux in a crucible can be undercooled nearly as strong as samples processed containerlessly by electromagnetic levitation. This allows to measure magnetic susceptibility on undercooled melts while combining the Faraday method with undercooling technique. The magnetic susceptibility of Co and Co-based alloys will be analysed as a function of temperature from superheated to undercooled state. This will be performed by measuring the change of magnetic force F Z on a sample in a constant magnetic field H 0 and an additional gradient field by means of a Faraday balance. When liquid Co-based alloys are undercooled the magnetisation steeply rises if temperature approaches the Curie temperature. The magnetisation is measured for some Co-based alloys in liquid state as function of alloy system and its concentration. The results show that the magnetic susceptibility of the liquid undercooled samples follows a Curie-Weiss behaviour, from which Curie temperature is inferred.

Surface tension, phase separation and solidification of undercooled Cu-Co

The system Cu-Co has a metastable miscibility gap in the under-cooled liquid phase which can be accessed by electromagnetic lévitation. Unsupported two-phase liquid drops display a variety of physical phenomena, including wetting, phase separation and solidification, which can be studied on this model system. This paper reports theoretical and experimental results which have been obtained within the CuCool project, funded by ESA, DLR and CNES through the MAP programme.