Regensburg 2007 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 30: Phase transitions III
MM 30.2: Vortrag
Donnerstag, 29. März 2007, 10:30–10:45, H4
The effect of melt convection on the secondary dendritic arm spacing of Nd-Fe-B alloys — •Kaushik Biswas1, Regina Hermann1, Horst Wendrock1, Gunter Gerbeth2, and Bernd Büchner1 — 1Leibniz Institute for Solid State and Materials Research (IFW) Dresden, P.O. Box 270116, D-01171 Dresden, Germany — 2Forschungszentrum Rossendorf (FZR), Institute of Safety Research, P.O. Box 510119, 01314 Dresden, Germany
Dendritic microstructure is one of the major microstructural constituents of peritectic alloys. In the present work, the effect of melt convection on the secondary dendritic arm spacing (SDAS) and phase fraction of properitectic α-Fe was investigated during solidification of stoichiometric Nd-Fe-B alloys under forced crucible rotation technique. The resulting microstructure of the alloy in consideration of melt convection has been investigated using scanning electron microscopy and optical microscopy. The average SDAS was determined for each sample from the whole cross-section of the cylindrical test samples using image analysing software LEICA QWIN. A detailed statistical analysis of the spacing distribution was performed on the basis of the variation of SDAS values averaged from about 80 to 120 dendrites in different zones. The α-Fe volume fraction measured by vibrating sample magnetometer (VSM) reduces with increasing crucible rotation frequency. Similarly, the SDAS values decrease with increasing rotation frequency. These results are explained from the viewpoint of a reduced melt convection state under steady forced crucible rotation leading to a reduced effective mass transfer coefficient.