R-Fe-B Rare Earth Sintered Magnet and Method for Producing Same

• US 20080286595A1
• Filed: 03/01/2007
• Published: 11/20/2008
• Est. Priority Date: 03/03/2006
• Status: Active Grant

• Current Assignee: Proterial Ltd.
• Original Assignee: Hitachi Metals (Thailand) Ltd.
• Inventors: Morimoto, Hideyuki, Odaka, Tomoori, Yoshimura, Koshi
• Granted Patent: US 8,206,516 B2
• Time in Patent Office: Days
• US Class Current: 428/548
• CPC Class Codes: B22F 2009/044 by jet milling
• CPC Class Codes: B22F 2201/013 Hydrogen
• CPC Class Codes: B22F 2202/05 Use of magnetic field
• CPC Class Codes: B22F 2998/10 Processes characterised by the sequence of their steps
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: B22F 3/02 Compacting only
• CPC Class Codes: B22F 3/10 Sintering only
• CPC Class Codes: B22F 7/062 involving the connection or repairing of preformed parts
• CPC Class Codes: B22F 9/04 starting from solid material, e.g. by crushing, grinding or milling C22C1/1084 takes precedence; crushing, grinding or milling, in general, see the relevant subclasses, e.g. B02C
• CPC Class Codes: H01F 1/0577 sintered
• CPC Class Codes: H01F 41/0293 diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
• CPC Class Codes: Y10T 428/12028 Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, etc.]

Abstract

In a method for producing an R—Fe—B based rare-earth sintered magnet according to the present invention, first, provided is an R—Fe—B based rare-earth sintered magnet body including, as a main phase, crystal grains of an R₂Fe₁₄B type compound that includes a light rare-earth element RL, which is at least one of Nd and Pr, as a major rare-earth element R. Thereafter, the sintered magnet body is heated while a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb, is supplied to the surface of the sintered magnet body, thereby diffusing the heavy rare-earth element RH into the rare-earth sintered magnet body.

Claims

1. A method for producing an R—

Fe—

B based rare-earth sintered magnet, the method comprising the steps of;

(a) providing an R—

Fe—

B based rare-earth sintered magnet body including, as a main phase, crystal grains of an R₂Fe₁₄B type compound that includes a light rare-earth element RL, which is at least one of Nd and Pr, as a major rare-earth element R;

(b) arranging a bulk body including a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb, along with the R—

Fe—

B based rare-earth sintered magnet body in a processing chamber; and

(c) heating the bulk body and the R—

Fe—

B based rare-earth sintered magnet body to a temperature of 700°

C. to 1,000°

C., thereby diffusing the heavy rare-earth element RH into the R—

Fe—

B based rare-earth sintered magnet body while supplying the heavy rare-earth element RH from the bulk body to the surface of the R—

Fe—

B based rare-earth sintered magnet body.

2. The method of claim 1, wherein the step (c) includes arranging the bulk body and the R—

Fe—

B based rare-earth sintered magnet body out of contact with each other in the processing chamber and setting an average gap between the two bodies within the range of 0.1 mm to 300 mm.

3. The method of claim 1, wherein the step (c) includes setting a difference in temperature between the R—

Fe—

B based rare-earth sintered magnet body and the bulk body within 20°

C.

4. The method of claim 1, wherein the step (c) includes adjusting the pressure of an atmospheric gas in the processing chamber within the range of 10⁻

5 Pa to 500 Pa.

5. The method of claim 1, wherein the step (c) includes maintaining the temperatures of the bulk body and the R—

Fe—

B based rare-earth sintered magnet body within the range of 700°

C. to 1,000°

C. for 10 minutes to 600 minutes.

6. The method of claim 1, wherein the sintered magnet body includes 0.1 mass % to 5.0 mass % of a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb.

7. The method of claim 6, wherein the content of the heavy rare-earth element RH in the sintered magnet body is within the range of 1.5 mass % to 3.5 mass %.

8. The method of claim 1, wherein the bulk body includes an alloy of the heavy rare-earth element RH and an element X, which is at least one element selected from the group consisting of Nd, Pr, La, Ce, Al, Zn, Sn, Cu, Co, Fe, Ag and In.

9. The method of claim 8, wherein the element X is at least one of Nd and Pr.

10. The method of claim 1, further comprising the step of subjecting the R—

Fe—

B based rare-earth sintered magnet body to an additional heat treatment process after the step (c) has been performed.

11. A method for producing an R—

Fe—

B based rare-earth sintered magnet, the method comprising the steps of;

(A) arranging a compact of an R—

Fe—

B based rare-earth magnet powder, including a light rare-earth element RL (which is at least one of Nd and Pr) as a major rare-earth element R, in a processing chamber such that the compact faces a bulk body including a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb;

(B) performing a sintering process in the processing chamber, thereby making an R—

Fe—

B based rare-earth sintered magnet body including crystal grains of an R₂Fe₁₄B type compound as a main phase; and

(C) heating the bulk body and the R—

Fe—

B based rare-earth sintered magnet body in the processing chamber, thereby diffusing the heavy rare-earth element RH into the R—

Fe—

B based rare-earth sintered magnet body while supplying the heavy rare-earth element RH from the bulk body to the surface of the R—

Fe—

B based rare-earth sintered magnet body.

12. The method of claim 11, wherein the step (B) includes performing the sintering process for 30 minutes to 600 minutes with a vacuum of 1 Pa to 10⁵ Pa created in the processing chamber and with an atmosphere in the processing chamber maintained at a temperature of 1,000°

C. to 1,200°

C.

13. The method of claim 11, wherein the step (C) includes performing the heating process for 10 minutes to 600 minutes with a vacuum of 1×

10<sup>−

5</sup> Pa to 1 Pa created in the processing chamber and with an atmosphere in the processing chamber maintained at a temperature of 800°

C. to 950°

C.

14. The method of claim 11, further comprising the step (B′

) of adjusting the degree of vacuum in the processing chamber within the range of 1×

10<sup>−

5</sup> Pa to 1 Pa after the temperature of the atmosphere in the processing chamber has decreased to 950°

C. or less and after the step (B) has been performed.

15. The method of claim 11, further comprising the step (B″

) of performing a heat treatment process for 30 minutes to 300 minutes with the degree of vacuum in the processing chamber adjusted within the range of 1×

10<sup>−

5</sup> Pa to 1 Pa and the temperature of the atmosphere in the processing chamber controlled within the range of 1,000°

C. to 1,200°

C. and then lowering the temperature in the processing chamber to 950°

C. or less after the step (B) has been performed.

16. An R—

Fe—

B based rare-earth sintered magnet comprising, as a main phase, crystal grains of an R₂Fe₁₄B type compound that includes a light rare-earth element RL (which is at least one of Nd and Pr) as a major rare-earth element R,

wherein the magnet further includes a heavy rare-earth element RH (which is at least one element selected from the group consisting of Dy, Ho and Tb and) which has been introduced from its surface by grain boundary diffusion, and

wherein in a surface region of the magnet, which is defined from the surface to a depth of 100 μ

m, there is a difference of at least 1 at % between the concentration of the heavy rare-earth element RH at a center portion of the crystal grains of the R₂Fe₁₄B type compound and that of the heavy rare-earth element RH on a grain boundary phase of the crystal grains of the R₂Fe₁₄B type compound.