Abstract
Recent progress in hydrogenation-decomposition-desorption-recombination (HDDR) process technologies is described with regard to the commercial production of Nd-Fe-B magnet powders. The applications of the powders to resin-bonded magnets and hot-pressed magnets are also presented. The HDDR reaction kinetics is an essential factor for improvements in magnetic properties of the Nd-Fe-B powders. Modified HDDR process, i.e., annealing the decomposed alloys under an Ar atmosphere, and then evacuating them with the correct desorption rate, can enhance magnetic anisotropy and coercivities of the powders simultaneously. Utilizing the rapidly solidified alloy flakes as a starting material of the HDDR process induces higher anisotropy in the final powders than using the conventional book-mold cast ingots. This can be ascribed to the complete elimination of α-Fe before the HDDR process. By these improved process, the following powders can be now commercially produced: high Br-type with (BH)max of 302-342 kJ/m3, high Hc-type with HcJ of 1430-1590 kA/m, and super high Br-type with (BH)max of 350-390 kJ/m3. Compression-molded resin-bonded magnets with (BH)max up to 199 kJ/m3 can be fabricated from the super high Br-type powders. Fully dense magnets produced by hot pressing the oriented high Hc-type powders exhibit excellent thermal stabilities.
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