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US-12626843-B2 - Rare earth magnet and method for producing thereof

US12626843B2US 12626843 B2US12626843 B2US 12626843B2US-12626843-B2

Abstract

To provide an R—Fe—B-based rare earth magnet excellent in the squareness and magnetic properties at high temperatures, and method for producing thereof. The present disclosure relates to a rare earth magnet including a main phase 10 and a grain boundary phase 20 present around the main phase 10 , and a method for producing thereof. In the rare earth magnet of the present disclosure, the overall composition is represented, in terms of molar ratio, by the formula: (R 1 (1-x) La x ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v , wherein R 1 is a predetermined rare earth element, M 1 is a predetermined element, 0≤x≤0.1, 12.0≤y≤20.0, 0.1≤z≤0.3, 5.0≤w≤20.0, and 0≤v≤2.0. The main phase 10 has an R 2 Fe 14 B-type crystal structure, the average particle diameter of the main phase 10 is less than 1 μm, and the volume ratio of a phase having an RFe 2 -type crystal structure in the grain boundary phase 20 is 0.40 or less relative to the grain boundary phase 20.

Inventors

  • Noritsugu Sakuma
  • Tetsuya Shoji
  • Akihito Kinoshita
  • Akira Kato

Assignees

  • TOYOTA JIDOSHA KABUSHIKI KAISHA

Dates

Publication Date
20260512
Application Date
20210903
Priority Date
20201022

Claims (9)

  1. 1 . A rare earth magnet comprising a main phase and a grain boundary phase present around the main phase, wherein the overall composition is represented, in terms of molar ratio, by the formula: (R 1 (1-x) La x ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v , wherein R 1 is Nd, M 1 is one or more elements selected from the group consisting of Ga, Al, Cu and In, and unavoidable impurity elements, 0.01≤x≤0.1, 12.0≤y≤20.0, 0.15≤z≤0.3, 5.0≤w≤20.0, and 0.05≤v≤2.0, the main phase has an R 2 Fe 14 B crystal structure, wherein R is a rare earth element, the average particle diameter of the main phase is less than 1 μm, the volume ratio of a phase having an RFe 2 crystal structure in the grain boundary phase is 0.40 or less relative to the grain boundary phase, and an Nd/Cu alloy is diffused and infiltrated in the grain boundary phase.
  2. 2 . A method for producing the rare earth magnet according to claim 1 , comprising: preparing a molten alloy having a composition represented, in terms of molar ratio, by the formula: (R 1 (1-x) La x ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v , wherein R 1 is one or more elements selected from the group consisting of Nd, M 1 is one or more elements selected from the group consisting of Ga, Al, Cu and In, and unavoidable impurity elements, 0.01≤x≤0.1, 12.0≤y≤20.0, 0.1≤z≤0.3, 5.0≤w≤20.0, and 0.5≤v≤2.0, cooling the molten alloy at a rate of 5×10 5 to 5×10 7 ° C./sec to obtain a magnetic ribbon or a magnetic flake, and pressure-sintering the magnetic ribbon or magnetic flake to obtain a sintered body.
  3. 3 . The method for producing a rare earth magnet according to claim 2 , wherein the magnetic ribbon or magnetic flake is pressure-sintered at 550 to 750° C.
  4. 4 . The method for producing a rare earth magnet according to claim 2 , further comprising subjecting the sintered body to hot plastic working.
  5. 5 . The method for producing a rare earth magnet according to claim 2 , wherein: x and z satisfy z≤2x+0.2, and the method for producing further comprises: preparing a modifier having a composition represented, in terms of molar ratio, by the formula: R 2 (1-s) M 2 s , wherein R 2 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy and Ho, M 2 is composed of a metal element which is other than a rare earth element and can be alloyed with R 2 , and an unavoidable impurity elements, and 0.05≤s≤0.40, and causing the modifier diffused and infiltrated into the sintered body.
  6. 6 . The method for producing a rare earth magnet according to claim 5 , wherein the diffusive penetration is performed at 550 to 750° C.
  7. 7 . The method for producing a rare earth magnet according to claim 5 , wherein R 2 is Nd and Tb and M 2 is Cu and unavoidable impurity elements.
  8. 8 . The method for producing a rare earth magnet according to claim 2 , wherein M 1 is one or more elements selected from the group consisting of Ga, Al and Cu, and unavoidable impurity elements.
  9. 9 . A rare earth magnet comprising a main phase and a grain boundary phase present around the main phase, wherein the overall composition is represented, in terms of molar ratio, by the formula: (R 1 (1-x) La x ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v ·(R 2 (1-s) M 2 s ) t , wherein each of R 1 and R 2 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy and Ho, M 1 includes In and optionally one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, and Mn, and an unavoidable impurity element, M 2 is composed of a metal element which is other than a rare earth element and can be alloyed with R 2 , and unavoidable impurity elements, 0≤x≤0.1, 12.0≤y≤20.0, 0.1≤z≤0.3, 5.0≤w≤20.0, and 0≤v≤2.0, 0.05≤s≤0.40, and 0.1≤t≤10.0, x and z satisfy z≤2x+0.2, the main phase has an R 2 Fe 14 B-type crystal structure, wherein R is a rare earth element, the average particle diameter of the main phase is less than 1 μm, and the volume ratio of a phase having an RFe 2 -type crystal structure in the grain boundary phase is 0.40 or less relative to the grain boundary phase.

Description

TECHNICAL FIELD The present disclosure relates to a rare earth magnet and a method for producing thereof. More specifically, the present disclosure relates to an R—Fe—B-based rare earth magnet, wherein R is a rare earth element, and a method for producing thereof. BACKGROUND ART The R—Fe—B-based rare earth magnet has a main phase and a grain boundary phase present around the main phase. The main phase is a magnetic phase having an R2Fe14B-type crystal structure. This main phase enables obtaining high residual magnetization. Accordingly, the R—Fe—B-based rare earth magnet is often used for motors. In the case where a permanent magnet including the R—Fe—B-based rare earth magnet is used for motors, the permanent magnet is disposed under a periodically changing external magnetic field environment and therefore, the permanent magnet may be demagnetized due to an increase in the external magnetic field. When used for motors, the permanent magnet is required to undergo as little demagnetization as possible in response to an increase in the external magnetic field. A demagnetization curve shows the degree of demagnetization in response to an increase in the external magnetic field, and the demagnetization curve satisfying the requirement above has a square shape. Consequently, satisfying the above-described requirement is referred to as excellent squareness. Since a motor generates heat during its operation, the permanent magnet used for motors is required to have high residual magnetization at high temperatures. In the present description, regarding the magnetic properties, the high temperature refers to a temperature in the range from 100 to 200° C., particularly from 140 to 180° C. As R of the R—Fe—B-based rare earth magnet, Nd has been mainly selected, but the rapid spread of electric vehicles poses a concern over an escalating price of Nd. For this reason, use of inexpensive light rare earth elements is being studied as well. For example, Patent Literature 1 discloses an R—Fe—B-based rare earth magnet where light rare earth elements Ce and La are selected as R of the R—Fe—B-based rare earth magnet. In addition, Patent Literature 2 discloses an R—Fe—B-based rare earth magnet where part of Nd as R of the R—Fe—B-based rare earth magnet is replaced by Ce and part of Fe is replaced by Co. CITATION LIST Patent Literature [PTL 1] Japanese Unexamined Patent Publication No. 61-159708[PTL 2] International Publication WO2014/196605 SUMMARY OF INVENTION Technical Problem As in the R—Fe—B-based rare earth magnet disclosed in Patent Literature 1, when a light rare earth element is simply selected as R, the magnetic properties are reduced. As in the R—Fe—B-based rare earth magnet disclosed in Patent Literature 2, when part of Fe is replaced by a small amount of Co, this is known to increase the corrosion resistance. In addition, incorporation of Co is generally known to be effective in enhancing the magnetic properties at high temperatures, particularly, the residual magnetization at high temperatures. However, the squareness is deteriorated by the incorporation of Co. The present disclosure has been made to solve the problems above. An object of the present disclosure is to provide an R—Fe—B-based rare earth magnet with excellent squareness and magnetic properties at high temperatures, particularly, residual magnetization at high temperatures, and a method for producing thereof. Solution to Problem The present inventors have made many intensive studies to attain the object above and have accomplished the rare earth magnet of the present disclosure and the method for producing thereof. The rare earth magnet of the present disclosure and the method for producing thereof include the following aspects. <1> A rare earth magnet including a main phase and a grain boundary phase present around the main phase, whereinthe overall composition is represented, in terms of molar ratio, by the formula: (R1(1-x)Lax)y(Fe(1-z)Coz)(100-y-w-v)BwM1v, wherein R1 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy and Ho, M1 is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In and Mn, and unavoidable impurity elements,0≤x≤0.1,12.0≤y≤20.0,0.1≤z≤0.3,5.0≤w≤20.0, and0≤v≤2.0,the main phase has an R2Fe14B-type, wherein R is a rare earth element, crystal structure,the average particle diameter of the main phase is less than 1 μm, andthe volume ratio of a phase having an RFe2-type crystal structure in the grain boundary phase is 0.40 or less relative to the grain boundary phase.<2> A rare earth magnet including a main phase and a grain boundary phase present around the main phase, whereinthe overall composition is represented, in terms of molar ratio, by the formula: (R1(1-x)Lax)y(Fe(1-z)Coz)(100-y-w-v)BwM1v·(R2(1-s)M2s)t (wherein each of R1 and R2 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy and Ho, M1 is one or more elements selected from the group con