Abstract
The recently developed HDDR process has now been extended to production of hot-pressed magnets. The samples prepared to date exhibit intrinsic coercivities of ≈1200 kA/m, remanence of around 690 mT and BH max values of ≈90 kJ/m 3. Careful studies of the microstructures reveal that the magnets consist of Nd 2Fe 14B grains predominantly in the range 0.1 μm⩽ x⩽1.0 μm with a very small number of grains in the range 10 μm ⩽ x⩽35 μm. These larger grains exhibit a very regular morphology and appear to be the result of a very rapid growth of some of the smaller sub-micron grains. The starting composition of the cast material Nd 16Fe 76B 8 ensures that the magnets have ≈12% Nd-rich intergranular material; this low melting point phase has been found to assist in the densification process. However, SEM studies have shown that the Nd-rich material is very unevenly distributed throughout the hot-pressed magnet and little evidence can be found for its presence between the grains of Nd 2Fe 14B.
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