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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.55  No.10 (2014)  >  pp.1582-1586

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Effect of Annealing on Magnetic Properties of Ultrafine Jet-Milled Nd-Fe-B Powders

Michihide Nakamura1), Masashi Matsuura1), Nobuki Tezuka1), Satoshi Sugimoto1), Yasuhiro Une2), Hirokazu Kubo2), Masato Sagawa2)
1) Department of Materials Science, Graduate School of Engineering, Tohoku University 2) Intermetallics Co., Ltd.

This paper reports the effects of annealing on the magnetic properties of ultrafine Nd-Fe-B powders with an average particle size of 0.67 µm. The powder was fabricated from hydrogenation–disproportionation–desorption–recombination (HDDR)-treated Nd-Fe-B alloys by hydrogen decrepitation and helium jet milling. The coercivity of the ultrafine powders was slightly increased by annealing below 500°C, and was drastically increased by annealing above 600°C. These two stepwise increases in coercivity were attributed to hydrogen desorption and formation of a liquid Nd-rich phase. In addition, after annealing below 500°C, the coercivity (μ0Hc) of the ultrafine powder was higher than that of the conventional powder, which was prepared from a strip-cast Nd-Fe-B alloy power with a particle size of 1.12 µm, because of a decrease in particle size. In contrast, after annealing above 600°C, the μ0Hc of the ultrafine powder was smaller than that of the conventional powder. The rare earth element content (Nd + Pr) was lower in the ultrafine powders than in the conventional powder. These results indicate that the rare earth element content was insufficient in the ultrafine powders.

ultrafine neodymium-iron-boron powders, annealing temperature, magnetic properties, hydrogenation-disproportionation-desorption-recombination, helium jet mill

Received: April 21, 2014
Accepted: July 14, 2014 , Published online: September 25, 2014



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