Berlin 2012 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 38: Liquid and Amorphous Metals
MM 38.5: Vortrag
Mittwoch, 28. März 2012, 16:00–16:15, H 1029
Investigation of solidification dynamics of undercooled melts of Cu-Zr alloys — •Raphael Kobold1, Dieter Herlach1,2, and Ulrich Köhler2 — 1Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt, 51170 Köln, Germany — 2Institut für Festkörperphysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
In contrast to experiments with most undercooled binary alloys the velocity of dendritic growth of a Cu50Zr50 alloy does not increase monotonically with undercooling but passes through a maximum and then decreases. To study this behaviour we investigate Cu-Zr alloys with Zirconium concentrations ranging from 44 to 54 at.% including eutectic and intermetallic phases. We use electrostatic levitation technique to melt and undercool samples with a diameter of 2-3mm under ultra-high-vacuum. Containerless processing is an effective tool for undercooling metallic melts far below their equilibrium melting temperatures since heterogeneous nucleation on container walls is completely avoided. During crystallisation of the undercooled melt the heat of crystallisation is released. The rapid increase of the temperature at the solid-liquid interface makes the solidification front visible. The velocities of the solidification front are measured by using a high-speed camera with a maximum frame rate of 50 000 pictures per second. Furthermore, experiments for phase selection during rapid solidification of the undercooled Cu-Zr melts were performed at DESY Hamburg.