Regensburg 2004 – wissenschaftliches Programm
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M: Metallphysik
M 1: Hauptvortrag Dirk Holland-Moritz
M 1.1: Hauptvortrag
Montag, 8. März 2004, 09:30–10:00, H16
Diffraction experiments on undercooled metallic melts — •Dirk Holland-Moritz — DLR, Institut für Raumsimulation, D-51170 Köln
Following the pioneering work of Frank in 1952, an icosahedral short-range order should be energetically favoured in undercooled metallic melts. Although this hypothesis is nearly 50 years old, direct experimental information on the short-range order prevailing in undercooled metallic liquids is only available for a short time. This work presents recent investigations on the short-range order of stable and deeply undercooled liquids of the pure elements Ni, Co, Zr and Fe and alloys forming polytetrahedral phases (Al13(Fe,Co)4). The liquids were containerlessly processed und undercooled by use of the electromagnetic levitation technique which was combined with techniques of elastic neutron scattering and energy dispersive diffraction of synchrotron radiation in order to determine the structure factors of the liquids as a function of the temperature.
The measured structure factors are well described if an icosahedral short-range order is assumed to prevail in the melt. This short-range order is observed even at temperatures above the melting temperature and gets more pronounced if the liquids are undercooled. In the case of the Al-based alloy melts forming polytetrahedral phases, the investigations are indicative of a pronounced chemical order such that the first coordination shell around a transition metal atom consists preferentially of Al-atoms.
This work was supported by DFG under contract Nos. Ho1942/1, Ho1942/2 and Ho1941/4.