# US 2018/0025820 A1 · R-t-b based sintered magnet

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- Number: US 2018/0025820 A1
- Document ID: US20180025820A1
- Status: Published application
- Kind: A1
- Application number: 15/656,284
- Filed: 2017-07-21
- Published: 2018-01-25
- Earliest claimed: 2016-07-25
- Assignees: TDK Corporation
- Applicants: TDK Corporation
- Inventors: Ayato KAKOKI; Makoto IWASAKI; Tetsuya HIDAKA; Takuma HAYAKAWA
- Web page: https://patentgrep.com/patent/US20180025820A1

## CPC

- H01F 1/0577: {sintered}
- B22F 3/16: in successive or repeated steps
- 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)
- C22C 28/00: Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00
- C22C 30/02: containing copper
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/06: containing aluminium
- C22C 38/10: containing cobalt
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- H01F 41/0293: {diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets}
- B22F 2009/044: {by jet milling}
- B22F 2201/11: Argon
- B22F 2202/05: Use of magnetic field
- B22F 2301/45: Rare earth metals, i.e. Sc, Y, Lanthanides (57-71)
- B22F 2998/10: Processes characterised by the sequence of their steps
- B22F 2999/00: Aspects linked to processes or compositions used in powder metallurgy
- C22C 2202/02: Magnetic
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- B22F: WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER (making alloys by powder metallurgy C22C); APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- C22C: ALLOYS (treatment of alloys C21D, C22F)

## Abstract

An R-T-B based sintered magnet containing a first heavy rare earth element, in which R includes Nd, T includes Co and Fe, the first heavy rare earth element includes Tb or Dy, the R-T-B based sintered magnet has a region in which a concentration of the first heavy rare earth element decreases from the surface toward the inside, a first grain boundary phase which contains the first heavy rare earth element and Nd but does not contain Co is present in one cross section including the region, and an area occupied by the first grain boundary phase in one cross section including the region is 1.8% or less.

## Claims

### Claim 1

An R-T-B based sintered magnet, wherein
R includes Nd,
T includes Co and Fe, and
a total area of voids in one cross section of the R-T-B based sintered magnet is 0.2% or less of an area of the cross section.

### Claim 2

An R-T-B based sintered magnet comprising a first heavy rare earth element, wherein
R includes Nd,
T includes Co and Fe,
the first heavy rare earth element includes Tb or Dy,
the R-T-B based sintered magnet comprises a region having a concentration of the first heavy rare earth element decreasing from a surface toward an inside,
a first grain boundary phase which contains the first heavy rare earth element and Nd but does not contain Co is present in one cross section including the region, and
an area occupied by the first grain boundary phase in the cross section is 1.8% or less.

### Claim 3 (depends on 2)

The R-T-B based sintered magnet according to claim 2, wherein
a second grain boundary phase which contains Nd and Co but does not contain the first heavy rare earth element is further present in the region and
a ratio of an area of the first grain boundary phase to an area of the second grain boundary phase is 2.0 or less.

### Claim 4 (depends on 2)

The R-T-B based sintered magnet according to claim 2, further comprising a second heavy rare earth element, wherein
the second heavy rare earth element is substantially uniformly contained over the entire grain boundary phase of the R-T-B based sintered magnet and is a different kind of element from the first heavy rare earth element.

### Claim 5 (depends on 2)

The R-T-B based sintered magnet according to claim 2, wherein
a second grain boundary phase of a multiparticle grain boundary phase which contains Nd and Co and has a substantially uniform concentration of the first heavy rare earth element is further present in the region and
a ratio of an area of the first grain boundary phase to an area of the second grain boundary phase is 2.0 or less.

### Claim 6

A sintered magnet, wherein
a first heavy rare earth element contained in a heavy rare earth compound is diffused from a surface toward an inside of an R-T-B based sintered magnet by attaching the heavy rare earth compound to at least a part of the surface of the R-T-B based sintered magnet and heating the heavy rare earth compound, wherein
R includes Nd,
T includes Co and Fe,
the first heavy rare earth element includes Tb or Dy,
a first grain boundary phase which contains the first heavy rare earth element and Nd but does not contain Co is present in one cross section including a region having the first heavy rare earth element diffused,
an area occupied by the first grain boundary phase in the cross section is 1.8% or less,
a second grain boundary phase which contains Nd and Co but does not contain the first heavy rare earth element is further present in the region, and
a ratio of an area of the first grain boundary phase to an area of the second grain boundary phase is 2.0 or less.

### Claim 7 (depends on 6)

The sintered magnet according to claim 6, wherein the R-T-B based sintered magnet contains a second heavy rare earth element.

### Claim 8 (depends on 3)

The R-T-B based sintered magnet according to claim 3, further comprising a second heavy rare earth element, wherein
the second heavy rare earth element is substantially uniformly contained over the entire grain boundary phase of the R-T-B based sintered magnet and is a different kind of element from the first heavy rare earth element.