Dresden 2014 – scientific programme
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MA: Fachverband Magnetismus
MA 55: Poster II
MA 55.71: Poster
Friday, April 4, 2014, 10:30–13:30, P2
The mechanisms of the Dy Grain Boundary Diffusion Process in sintered NdFeB permanent magnets — •Konrad Löwe1, Christoph Brombacher2, Matthias Katter2, and Oliver Gutfleisch1 — 1TU Darmstadt, Materials Science, 64287 Darmstadt, Germany — 2VACUUMSCHMELZE GmbH & Co. KG, 63450 Hanau, Germany
We investigated the mechanisms of Dy diffusion in Nd-Fe-B permanent magnets. At optimum annealing conditions the Dy processed magnets yield a total coercivity increase of 4.5 kOe and a roughly constant remanence. The switching field distribution along the diffusion direction was measured with a hall probe. For an application of 0.3 wt% Dy and annealing at 900°C an increased coercivity was found up to a depth of about 3 mm. Microstructure analysis by WDX and TEM EDX revealed an enhanced Dy concentration in the surface region of the individual Nd-Fe-B grains. The Dy concentration in these so-called "shells" decreased exponentially from 6.0 at% at the surface of the magnet to about 1.8 at% after a diffusion depth of 0.4 mm. The mechanism of Dy-shell formation was reasoned to be melting/solidification of a rare earth rich intermediate phase during high-temperature annealing. This assumption is based on the fact that a constant Dy concentration over the width of a shell was found. With EBSD no orientation difference between the Nd-Fe-B grains and the surrounding shells has been found, which points to an epitaxial solidification of the melt on the grains.