Anisotropic HDDR epoxy bonded magnets from NdFeBZr

The hydrogenation disproportionation desorption recombination (HDDR) process has been established as an effective processing route for the production of isotropic NdFeB coercive powder. By the addition of very small amounts of zirconium to the initial composition, it has also been found that anisotropic powder can be produced during the HDDR process. Two compositions were selected for this work: Nd/sub 16/Fe/sub 75.9/B/sub 8/Zr/sub 0.1/ and Nd/sub 16/Fe/sub 75.7/B/sub 8/Zr/sub 0.3/. These alloys were processed at temperatures between 770 degrees C and 840 degrees C, and a maximum coercivity of 800 kA/m was achieved for the alloy containing 0.1 at.% Zr at a processing temperature of 795 degrees C, but the alloy containing 0.3 at.% Zr failed to exhibit any coercivity greater than 120 kA/m, across a wide range of processing temperatures. This can be attributed to a much larger final grain size for this material under the processing conditions used. Magnetic anisotropy is produced by the submicron grains of Nd/sub 2/Fe/sub 14/B recombining from the disproportionated structure with a preferred orientation distribution.<
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