DocumentCode :
3602324
Title :
Enhancement of Coercivity of Nd-Fe-B Ultrafine Powders Comparable With Single-Domain Size by the Grain Boundary Diffusion Process
Author :
Sugimoto, Satoshi ; Nakamura, Michihide ; Matsuura, Masashi ; Une, Yasuhiro ; Kubo, Hirokazu ; Sagawa, Masato
Author_Institution :
Dept. of Mater. ScienceGraduate Sch. of Eng., Tohoku Univ., Sendai, Japan
Volume :
51
Issue :
11
fYear :
2015
Firstpage :
1
Lastpage :
4
Abstract :
We describe the enhancement of coercivity of Nd-Fe-B ultrafine powders by the grain boundary diffusion (GBD) process. An effective method for increasing coercivity in Nd-Fe-B sintered magnets is the refinement of the Nd2Fe14B grains. We decreased the powder size of the grains to <;1 μm m by combining hydrogenation-disproportionation-desorption-recombination, hydrogen decrepitation, and helium jet milling (He-JM). The powder size was comparable with the single-domain size of Nd2Fe14B. However, the coercivity of the ultrafine powders was lower than the value expected from their powder size, which was due to the decrease in the Nd content of the powders and lack of the Nd-rich phase on the powder surface. We performed the GBD process at 700 °C for 30 min before He-JM to increase the amount of Nd-rich phase on the powder surface. The powder showed a high coercivity of μ0HeJ = 2 T after annealing at 600 °C for 30 min. Therefore, the GBD process is an effective method for increasing the coercivity of ultrafine He-JM powders. The process increases the amount of the Nd-rich phase on the powder surface, which is converted to the liquid phase by annealing, and reduces the number of sites for reverse domain nucleation.
Keywords :
annealing; boron alloys; coercive force; desorption; grain boundary diffusion; hydrogenation; iron alloys; magnetic particles; neodymium alloys; sintering; GBD process; NdFeB; annealing; coercivity; grain boundary diffusion; helium jet milling; hydrogen decrepitation; hydrogenation-disproportionation-desorption-recombination; liquid phase; powder size; powder surface; reverse domain nucleation; sintered magnets; temperature 600 degC; temperature 700 degC; time 30 min; ultrafine He-JM powders; Annealing; Coercive force; Grain boundaries; Magnetic domains; Magnetic resonance imaging; Metals; Powders; Coercivity; coercivity; grain boundary diffusion (GBD) process; grain boundary diffusion process; helium jet mill; helium jet mill (He-JM); hydrogen decrepitation (HD); hydrogen-decrepitation; hydrogenation-disproportionation-desorption-recombination; hydrogenation-disproportionation-desorption-recombination (HDDR); neodymium-iron-boron; neodymium-iron-boron (Nd-Fe-B);
fLanguage :
English
Journal_Title :
Magnetics, IEEE Transactions on
Publisher :
ieee
ISSN :
0018-9464
Type :
jour
DOI :
10.1109/TMAG.2015.2434889
Filename :
7109905
Link To Document :
بازگشت