# US 11,309,108 B2 · R-T-B based permanent magnet

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- Number: US 11,309,108 B2
- Document ID: US11309108B2
- Status: Granted
- Kind: B2
- Application number: 16/818,308
- Filed: 2020-03-13
- Published: 2020-09-24
- Granted: 2022-04-19
- Earliest claimed: 2019-03-18
- Assignees: TDK Corporation
- Applicants: TDK Corporation
- Inventors: Hikaru Kudo
- Web page: https://patentgrep.com/patent/US11309108B2

## CPC

- H01F 1/0577: {sintered}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/10: containing cobalt
- C22C 38/16: containing copper
- H01F 7/02: Permanent magnets {[PM]}
- H01F 41/0293: {diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets}
- Y02T 10/64: Electric machine technologies in electromobility
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

A permanent magnet includes Nd, Fe, B, and Ga and contains a first T rich phase 1, a second T rich phase 3, and a T poor phase 5 as grain boundary phases, the first T rich phase 1 satisfies 1.7≤[T]/[R]≤3.0, the second T rich phase 3 satisfies 0.8≤[T]/[R]≤1.5, the T poor phase 5 satisfies 0.0≤[T]/[R]≤0.6, and the following Formulas 4 and 5 are satisfied. [T] represents the concentration (atom %) of Fe and Co, [R] represents the concentration (atom %) of Nd, Pr, Tb, and Dy, S1 represents the area of the first T rich phase 1 exposed at a cross-section of the permanent magnet, S2 represents the area of the second T rich phase 3 exposed at the cross-section, and S3 represents the area of the T poor phase 5 exposed at the cross-section. 0.30≤(S1+S2)/(S1+S2+S3)≤0.80 (4) 0.20≤S2/(S1+S2)≤0.80 (5)

## Claims

### Claim 1

An R-T-B based permanent magnet including a rare earth element R, a transition metal element T, B, and Ga,
wherein the R-T-B based permanent magnet includes at least Nd as R,
the R-T-B based permanent magnet includes at least Fe as T,
the R-T-B based permanent magnet comprises a plurality of main phase grains containing Nd, T, and B; and grain boundaries surrounded by a plurality of the main phase grains,
at least a portion of the grain boundaries contains a first T rich phase,
at least a portion of the grain boundaries contains a second T rich phase,
at least a portion of the grain boundaries contains a T poor phase,
the first T rich phase is a phase containing Nd, Ga, and at least one of Fe and Co and satisfying the following Formula 1,
the second T rich phase is a phase containing Nd, Ga, and at least one of Fe and Co and satisfying the following Formula 2,
the T poor phase is a phase containing Nd and satisfying the following Formula 3,
the first T rich phase, the second T rich phase, and the T poor phase satisfy the following Formula 4, and
the first T rich phase and the second T rich phase satisfy the following Formula 5:
1.7≤[T]/[R]≤3.0 (1)
0.8≤[T]/[R]≤1.5 (2)
0.0≤[T]/[R]≤0.6 (3)
wherein [T] in the Formula 1 represents the sum of the concentrations of Fe and Co in the first T rich phase; [R] in the Formula 1 represents the sum of the concentrations of Nd, Pr, Tb, and Dy in the first T rich phase; [T] in the Formula 2 represents the sum of the concentrations of Fe and Co in the second T rich phase; [R] in the Formula 2 represents the sum of the concentrations of Nd, Pr, Tb, and Dy in the second T rich phase; [T] in the Formula 3 represents the sum of the concentrations of Fe and Co in the T poor phase; [R] in the Formula 3 represents the sum of the concentrations of Nd, Pr, Tb, and Dy in the T poor phase; and the respective units of [T] and [R] in the Formula 1, the Formula 2, and the Formula 3 are atom %,
0.30≤(S1+S2)/(S1+S2+S3)≤0.80 (4)
0.20≤S2/(S1+S2)≤0.80 (5)
wherein S1 in the Formula 4 and the Formula 5 represents the sum of the areas of the first T rich phase exposed at a cross-section of the R-T-B based permanent magnet; S2 in the Formula 4 and the Formula 5 represents the sum of the areas of the second T rich phase exposed at the cross-section of the R-T-B based permanent magnet; and S3 in the Formula 4 represents the sum of the areas of the T poor phase exposed at the cross-section of the R-T-B based permanent magnet.

### Claim 2 (depends on 1)

The R-T-B based permanent magnet according to claim 1, wherein
the R-T-B based permanent magnet comprises grain boundary multiple junctions surrounded by three or more of the main phase grains, as the grain boundaries, and
both of the second T rich phase and the T poor phase exist within one grain boundary multiple junction.

### Claim 3 (depends on 1)

The R-T-B based permanent magnet according to claim 1, wherein the R-T-B based permanent magnet is composed of 29.50% to 33.00% by mass of R;
0.70% to 0.95% by mass of B;
0.03% to 0.60% by mass of Al;
0.01% to 1.50% by mass of Cu;
0.00% to 3.00% by mass of Co;
0.10% to 1.00% by mass of Ga;
0.05% to 0.30% by mass of C;
0.03% to 0.40% by mass of O; and
the balance, and
the balance is Fe only, or Fe and other elements.

### Claim 4 (depends on 1)

The R-T-B based permanent magnet according to claim 1, wherein the sum of the contents of heavy rare earth elements is from 0.00% by mass to 1.00% by mass.

### Claim 5 (depends on 1)

The R-T-B based permanent magnet according to claim 1, wherein the T poor phase contains at least one of Cu and Ga.