Rare-earth magnet and method for producing the same

Patent metadata

Field	Value
Publication number	US-10199145-B2
Application number	US-201214237702-A
Country	US
Kind code	B2
Filing date	Nov 12, 2012
Priority date	Nov 14, 2011
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

Provided is a rare-earth magnet containing no heavy rare-earth metals such as Dy or Tb in a grain boundary phase, has a modifying alloy for increasing coercivity (in particular, coercivity under a high-temperature atmosphere) infiltrated thereinto at lower temperature than in the conventional rare-earth magnets, has high coercivity, and has relatively high magnetizability, and a production method therefor. The rare-earth magnet RM includes a RE-Fe—B-based main phase MP with a nanocrystalline structure (where RE is at least one of Nd or Pr) and a grain boundary phase BP around the main phase, the grain boundary phase containing a RE-X alloy (where X is a metallic element other than heavy rare-earth elements). Crystal grains of the main phase MP are oriented along the anisotropy axis, and each crystal grain of the main phase, when viewed from a direction perpendicular to the anisotropy axis, has a plane that is quadrilateral in shape or has a close shape thereto.

First claim

The invention claimed is:

1. A rare-earth bulk magnet comprising:
a RE-Fe—B-based main phase with a nanocrystalline structure, the main phase having crystal grain size in a range of 50 nm to 300 nm, where RE is at least one of Nd or Pr; and; and
a grain boundary phase around the main phase, the grain boundary phase containing a RE-X alloy, where X is a metallic element other than heavy rare-earth elements,
wherein crystal grains of the main phase are oriented along an anisotropy axis,
each crystal grain of the main phase, when viewed from a direction perpendicular to the anisotropy axis, has a plane that is quadrilateral in shape or has a close shape thereto,
a solid shape of the crystal grain of the main phase has a (001) plane as a plane that is perpendicular to the anisotropy axis, and has (110), (100), or a close low-index plane thereto as a side plane, and
a coercivity of the rare-earth bulk magnet satisfies the following formula (1):
Hc=αHa−NMs   (1),

wherein, in formula (1), Hc denotes coercivity, α denotes a factor attributable to a separation property between nanocrystalline grains of the main phase, Ha denotes magnetocrystalline anisotropy, which is specific to a material of the main phase, N denotes a factor attributable to a grain size of the main phase, and Ms denotes saturation magnetization, which is specific to the material of the main phase, and
αis in a range of 0.42 to 0.52, and N is in a range of 0.68 to 0.90 and
wherein the rare-earth bulk magnet is obtained by:
Step 1: sintering a powder, obtained through liquid quenching of a melt of a RE-Fe—B-based metal, at a temperature of 500 to 700° C., a pressure of 50 to 500 Mpa, and a time of 10 to 600 seconds to obtain a bulk sintered body having an isotropic crystalline structure; and
Step 2: applying hot plastic processing to the bulk sintered body obtained in Step 1 at a temperature of 700 to 800° C., a predetermined plastic strain rate, a predetermine pressure and a predetermined processing time to obtain a molded body with magnetic anisotropy imparted thereto along the anisotropy axis, the molded body having the RE-Fe—B-based main phase and the grain boundary phase around the main phase; and
Step 3: melting a RE-Z modifying alloy, where Z is a metallic element other than heavy rare-earth elements, for increasing coercivity of the molded body obtained in Step 3, together with the grain boundary phase, to cause liquid-phase infiltration of a melt of the RE-Z modifying alloy from a surface of the molded body, thereby obtaining the rare-earth bulk magnet, and
wherein pressure is applied in Step 1 and Step 2 using a punch, and after the bulk sintered body is obtained in Step 1, an end face of the bulk sintered body is made to abut the punch so as to impart the anisotropy to the bulk sintered body during Step 2.

2. The rare-earth bulk magnet according to claim 1 , wherein the RE-Z modifying alloy is a Nd—Cu alloy.

3. The rare-earth bulk magnet according to claim 1 , wherein the RE-Z modifying alloy is a Nd—Al alloy.

4. The rare-earth bulk magnet according to claim 1 , wherein X is at least one element selected from the group consisting of Co, Fe and Ga, and Z is an element selected from the group consisting of Cu and Al.

5. The rare-earth bulk magnet according to claim 1 , wherein the RE-Z modifying alloy is a Nd—Cu alloy, and Step 3 includes melting the Nd—Cu alloy together with the grain boundary phase at a temperature of 520 to 600° C. to cause the liquid-phase infiltration of a melt of the Nd—Cu alloy.

6. The rare-earth bulk magnet according to claim 1 , wherein the RE-Z modifying alloy is a Nd—Al alloy, and Step 3 includes melting the Nd—Al alloy together with the grain boundary phase at a temperature of 640 to 650° C. to cause the liquid-phase infiltration of a melt of the Nd—Al alloy.

Assignees

• Toyota Motor Co Ltd

Inventors

• Shoji Tetsuya
• Manabe Akira
• Miyamoto Noritaka
• Hiraoka Motoki
• Omura Shinya
• Ichigozaki Daisuke
• Nagashima Shinya

Classifications

• B22F3/26

  Impregnating {(making ferrous alloys by impregnation C22C33/0242)} · CPC title

• H01F41/0253

  for manufacturing permanent magnets · CPC title

• H01F1/0577

  sintered · CPC title

• B22F3/10

  Sintering only · CPC title

• C22C28/00 Primary

  Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00 · CPC title