Intermetallics Co., Ltd.
Abstract:
A useful method for improving the coercivity of Nd-Fe-B sintered magnets without heavy-rare-earth element addition is grain refinement of the Nd2Fe14B crystal [1,2]. We decreased the particle size of jet-milled powders to around 1.1 µm by applying He jet milling to strip-cast (SC) Nd-Fe-B alloys [3]. Using these He jet-milled powders, we achieved high coercivity of 20 kOe with grain-refined HREE-free Nd-Fe-B sintered magnets. Furthermore, we obtained sub-micron Nd-Fe-B powder using hydrogenation-disproportionation-desorption-recombination (HDDR) treatment and He jet milling [4]. We have been developing the sub-micron grained HREE-free Nd-Fe-B sintered magnets using this fine powder. The magnet has a high orientation ratio of 95% and a good temperature coefficient of coercivity. It has been found that the magnets have distinctive minor hysteresis curves like a single magnetic domain type in a First-order-reversal-curves (FORCs) measurement at 180 ℃.
On the other hand, the fine-grained HDDR-processed magnets have a low coercivity of around 13 kOe at room temperature. We think that the low coercivity is due to the thinner grain boundary with the thickness of 1 nm than the conventional sintered magnet with the thickness of 2 nm.
In the workshop, we will talk about the magnetic properties and microstructure of the fine-grained magnet, and show the recent trial for obtaining higher coercivity by thickening technique of the grain boundary phase such as Ga-doping or grain boundary diffusion.
On the other hand, the fine-grained HDDR-processed magnets have a low coercivity of around 13 kOe at room temperature. We think that the low coercivity is due to the thinner grain boundary with the thickness of 1 nm than the conventional sintered magnet with the thickness of 2 nm.
In the workshop, we will talk about the magnetic properties and microstructure of the fine-grained magnet, and show the recent trial for obtaining higher coercivity by thickening technique of the grain boundary phase such as Ga-doping or grain boundary diffusion.
[1] M. Sagawa, Development and Prospect of the Nd-Fe-B Sintered Magnets, Proc. of 21st International Workshop on REPM, Bled, Slovenia (2010) 183-186.
[2] T. Fukada, M. Matsuura, R. Goto, N. Tezuka, S. Sugimoto, Y. Une, and, M. Sagawa, Evaluation of the Microstructural Contribution to the Coercivity of Fine-Grained Nd–Fe–B Sintered Magnets, Mater. Trans.53, (2012) 1967-1971.
[3] Y. Une, and, M. Sagawa, Ultla-Fine Grained Nd2Fe14B Sintered Magnets, J. Jpn. Inst. Met. 76 (2012) 12 (in Japanese).
[4] M. Nakamura, M. Matsuura, N. Tezuka, S. Sugimoto, Y. Une, H. Kubo, and, M. Sagawa, Preparation of ultrafine jet-milled powders for Nd-Fe-B sintered magnets using hydrogenation-dispropotionation-desorption-recombination and hydrogen decrepitation processes, Appl. Phys. Lett. 103 (2013) 022404.
[2] T. Fukada, M. Matsuura, R. Goto, N. Tezuka, S. Sugimoto, Y. Une, and, M. Sagawa, Evaluation of the Microstructural Contribution to the Coercivity of Fine-Grained Nd–Fe–B Sintered Magnets, Mater. Trans.53, (2012) 1967-1971.
[3] Y. Une, and, M. Sagawa, Ultla-Fine Grained Nd2Fe14B Sintered Magnets, J. Jpn. Inst. Met. 76 (2012) 12 (in Japanese).
[4] M. Nakamura, M. Matsuura, N. Tezuka, S. Sugimoto, Y. Une, H. Kubo, and, M. Sagawa, Preparation of ultrafine jet-milled powders for Nd-Fe-B sintered magnets using hydrogenation-dispropotionation-desorption-recombination and hydrogen decrepitation processes, Appl. Phys. Lett. 103 (2013) 022404.
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