Rina Takizawa 1, Hiroshi Akamine 1, 2, Masaru Itakura 1, 2, Minoru Nishida 1, 2, Nobuhiro Katayama 3 and Koichiro Morimoto 3
1 Department of Applied Science for Electronics and Materials, Interdisciplinary Graduate School of Science and Engineering, Kyushu University
In the hydrogenation-decomposition-desorption-recombination (HDDR) processed Nd-Fe-Co-B-Al-Ga-Zr magnet powders, influence of the desorption-recombination (DR) temperatures on the microstructures was investigated by high-resolution scanning electron microscopy and scanning transmission electron microscopy. By applying the DR treatment under high vacuum (DR-Step 2) at relative low temperatures about 973 K, we can obtain the excellent texture in which the average size of Nd2Fe14B grains is refined to about 240 nm and the grain boundary (GB) phase is uniformly dispersed around the Nd2Fe14B grains. In the GB phase, furthermore, the Nd composition increases and the (Fe, Co) composition decreases drastically with decreasing the DR temperatures, and then Nd-rich GB phase with more than 65 at.%Nd can be formed at 973 K. At 973 K, however, the region with unformed GB phase is remained about 10% of the specimen, which leads to deterioration of the coercivity. It was found that the gently DR treatment is very effective not only for increasing the coercivity but also for improving the squareness in demagnetization curve.
neodymium-iron-boron magnet, hydrogenation-decomposition-desorption-recombination process, electron microscopy, coercivity
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