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MA: Fachverband Magnetismus

MA 13: Magnetic Materials II

MA 13.6: Talk

Monday, March 14, 2011, 18:15–18:30, HSZ 401

HDDR - An efficient way to produce highly coercive, anisotropic Nd-Fe-B powders — •Konrad Güth, Thomas George Woodcock, Juliane Thielsch, Ludwig Schultz, and Oliver Gutfleisch — IFW Dresden, Institut für Metallische Werkstoffe, Postfach 270016, D-01171 Dresden, Germany

Nd-Fe-B sintered magnets have the highest energy product, (BH)_max, of any commercially available hard magnetic material (typically 300-400 kJ/m³). Disadvantages of Nd-Fe-B sintered magnets are the relatively high cost and their machinability. One promising approach to achieve relatively high performance with lower material cost is to process the Nd-Fe-B powder using a hydrogen treatment at elevated temperature. This method is known as the HDDR (hydrogenation, disproportionation, desorption, recombination) process. HDDR has been shown to be an effective route to produce a Nd₂Fe₁₄B powder with a highly refined grain size (about 300 nm) compared to that of the starting material (typically tens of µm). Coercivity has been shown to increase with decreasing grain size. A further, very specific advantage of the HDDR process is the texture-memory effect. This means that the refined grains within a particle exhibit a texture which is derived from the orientation of the original, coarse grain. Strong texture is necessary to maximize the remanence, yielding anisotropic polymer bonded magnets. In the current work, microstructural investigation based on SEM and XRD of different stages of the HDDR process will be given. The magnetic properties in dependence on the hydrogen pressure during processing are studied by VSM.