Viskositäten unterkühlter Metallschmelzen
In this thesis two methods are described to measure the viscosity of a undercooled liquid metal. One method used in a facility on the earth under 1 g conditions, while the second was applied under microgravity conditions during a flight of the TEMPUS facility on board of the space shuttle. Both methods are containerless processing methods and allow to undercool liquid metals, because of the reduced heterogeneous nucleation. Measurements in earthbound levitation facilities under 1g: In electromagnetic levitation facilities the high frequent levitation field can be modulated with a low frequency in order to excite a forced oscillation. With the use of digital image analysis the amplitude of the forced oscillations can be determined and the resonance curve can be found. By fitting the theoretical function of the amplitudes of a forced oscillation on the data the damping constant can be determined. A comparison of the viscosity values calculated from the damping constants with literature values shows that these values are one order of magnitude too high. In opposite to experiments under microgravity the strong magnetic field also introduces a magnetic damping. The effect of this magnetic damping can be estimated with the Hartmann number, which is the quotient of the magnetic and molecular damping. A comparison of the Hartmann numbers for the experiments on earth and the calculated damping constants shows that this theory gives a good estimation for the experiments under 1g. Experiments under microgravity: In order to reduce the damping effect of strong magnetic field experiments under microgravity have been performed. Under microgravity is no field necessary to lift the sample only a small positioner field is needed. These experiments have been performed with the TEMPUS (Tiegelfreies elektromagnetisches Prozessieren unter Schwerelosigkeit) facilty. With a pulse of the heating voltage the sample could be excited to an oscillation. From this oscillation the amplitude could be measured and from the time dependence of the amplitude the damping of the oscillation could be determined. From the damping the viscosity for Co80Pd20 and could be calculated. For Co80Pd20 the viscosity could be measured up to undercoolings of 300 K. Pd76Cu6Si18 is a glassforming alloy and the temperature dependant viscosity was described with three models for the viscosity. Due to the limited temperature range it was not possible to find out which models gives the best description of the data.
info:eu-repo/classification/ddc/530, Metallschmelze, Unterkühlung, Viskosität, Schwerelosigkeit, Physik, Metall, flüssig, unterkühlt
Networked Digital Library of Theses and Dissertations
Publikationsserver der RWTH Aachen University