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MA: Magnetismus

MA 8: Hart- und Weichmagn. Materialien / Legierungen

MA 8.4: Vortrag

Dienstag, 12. März 2002, 14:30–14:45, H10

Solidification behaviour and TiC precipitation phenomena in Nd-Fe-B-Ti-C melts — •Octavian Filip, Regina Hermann, and Ludwig Schultz — IFW Dresden, Postfach 270016, D-01171 Dresden

The solidification behaviour and phase selection phenomena of stoichiometric Nd-Fe-B alloys with Ti and C additions (0.5 to 3 at%) were investigated using the electromagnetic levitation and melt spinning techniques. A strong reduction of the solidification front velocity was observed in undercooled Nd-Fe-B-Ti-C alloys compared to the addition-less Nd-Fe-B alloy. The TiC precipitation phenomena in overheated and undercooled stages were found to play an important role on phase selection and grain structure. The cooling rate prior to solidification influences drastically the morphology of the TiC precipitates, which affects strongly the nucleation of the properitectic γ-Fe in the undercooled stage. High quenching rates promote the formation of fine TiC precipitates. The solubility of Ti in the hard magnetic Nd₂Fe₁₄B₁ phase was found to be negligible. TEM investigations of melt spun Nd-Fe-B-Ti-C ribbons showed that nano-size TiC particles are situated in the intra- or inter-granular region. The fine dispersed TiC precipitates act as nucleants for the formation of the hard magnetic grains. The correlation between the increasing nucleation rate and the considerable grain refinement is pronounced. Annealing at elevated temperatures promotes further TiC precipitation at the grains boundaries leading to a stable fine grained microstructure.