JP2020161692A - R-t-b based permanent magnet - Google Patents

Abstract

To provide an R-T-B based permanent magnet which is improved in temperature characteristic, especially the temperature characteristic of a coercive force (Hcj).SOLUTION: An R-T-B based permanent magnet contains Cr. In the magnet, R is at least one kind selected from rare earth elements, T is Fe solely, or Fe and Co, and B is boron. The R-T-B based permanent magnet comprises a primary-phase grain and a grain boundary phase which is present in a grain boundary. The magnet includes, as the grain boundary phase, an R-rich phase. The primary-phase grain has a greater Cr content than the R-rich phase.SELECTED DRAWING: Figure 1

Description

The present invention relates to RTB-based permanent magnets.

Patent Document 1 describes the invention of a rare earth magnet. In particular, rare earth magnets having a high square ratio and heat resistance even if the B content is relatively low by containing Cu and Co within a specific range are described.

Patent Document 2 describes the invention of an R-TM-B-based sintered magnet. In particular, R-TM-B-based sintered magnets having excellent corrosion resistance and mechanical properties even when the Co content is significantly reduced are described.

International Publication No. 2015/078362 International Publication No. 2016/158552

An object of the present invention is to provide an RTB-based permanent magnet having improved temperature characteristics, particularly the temperature characteristics of coercive force (Hcj).

In order to achieve the above object, the RTB-based permanent magnet according to the present invention is
An RTB-based permanent magnet containing Cr.
R is one or more selected from rare earth elements, T is Fe alone or Fe and Co, and B is boron.
The RTB-based permanent magnet includes a main phase particle and a grain boundary phase existing at a grain boundary.
An R-rich phase is included as the grain boundary phase,
The main phase particles are characterized by having a higher Cr content than the R-rich phase.

The RTB-based permanent magnet according to the present invention has the above-mentioned structure and Cr distribution, so that the temperature characteristics of the RT-B-based permanent magnet having a relatively low B content, particularly the temperature of Hcj. The characteristics can be improved.

The temperature characteristic of Hcj is better as the absolute value of the temperature coefficient of Hcj is smaller. The temperature coefficient of Hcj is a value indicating what percentage of Hcj changes per 1 ° C. of temperature change. When the reference temperature is T1, the target temperature is T2, the Hcj at the reference temperature is Hcj1, and the Hcj at the target temperature is Hcj2, then [{(Hcj2-Hcj1) / Hcj1} / (T2-T1)] × 100 It is calculated.

R may contain one or more selected from Nd and Pr.

It may also contain Ga.
The R-rich phase may include an R ₆ T ₁₃ Ga phase.
The Cr content in the R ₆ T ₁₃ Ga phase may be 0% by mass or more and less than 0.30% by mass.

T may be Fe and Co, and may further contain Ga and Cu.
The R-rich phase may include an R-Co-Cu-Ga phase.
The Cr content in the R—Co—Cu—Ga phase may be 0% by mass or more and less than 0.20% by mass.

It may also contain Zr.
The grain boundary phase may include a Zr-B phase and / or a Zr-C phase.

T may be Fe and Co, and may further contain Ga, M1 and M2.
M1 is one or more selected from Zr, Ti, Hf, Nb, V, Mo, and W and contains at least Zr.
M2 is one or more selected from Cu and Al.
Taking the entire RTB-based permanent magnet as 100% by mass,
The total content of R is 28.00% by mass or more and 34.00% by mass or less,
Co content is 0.30% by mass or more and 3.00% by mass or less,
B content is 0.70% by mass or more and 0.95% by mass or less,
Cr content is 0.05% by mass or more and 0.50% by mass or less,
Ga content is 0.30% by mass or more and 1.00% by mass or less,
The total content of M1 is 0.10% by mass or more and 3.00% by mass or less,
Zr content is 0.10% by mass or more and 1.50% by mass or less,
The total content of M2 may be greater than 0% by mass and less than or equal to 2.00% by mass.
Fe may be the substantial balance.

The total content of R may be the total content of Nd and Pr.

It is an SEM image of the RTB system permanent magnet which concerns on this embodiment.

Hereinafter, the present invention will be described based on the embodiments.

<RTB Permanent Magnet>
The RTB-based permanent magnet according to this embodiment will be described.

The RTB-based permanent magnet according to the present embodiment has a specific fine structure, so that the temperature characteristics can be improved. Hereinafter, the fine structure of the RTB-based permanent magnet according to the present embodiment will be described.

The RTB-based permanent magnet according to the present embodiment has a grain boundary formed by a main phase particle having an R ₂ T ₁₄ B type crystal structure and two or more adjacent main phase particles. The grain boundaries are classified into two-particle grain boundaries formed by two main-phase particles and multi-particle grain boundaries formed by three or more main-phase particles. In addition, one or more kinds selected from Nd and Pr may be included as R.

In the RTB-based permanent magnet according to the present embodiment, a grain boundary phase exists at the grain boundary. The RTB-based permanent magnet according to the present embodiment includes an R-rich phase as a grain boundary phase. The R-rich phase is a phase in which the R content is higher than that of the main phase particles. The main phase particles contained in the RTB-based permanent magnet according to the present embodiment have a higher Cr content than the R-rich phase. The Cr content in all the main phase particles does not have to be higher than the Cr content in all R-rich phases, but the Cr content in the main phase particles of 70% or more on a number basis is arbitrary R. It may be higher than the Cr content in the rich phase.

Further, the Cr content in the main phase particles may be 0.01% by mass or more, or 0.05% by mass or more, more than the Cr content in the R-rich phase.

The RTB-based permanent magnet according to the present embodiment has better temperature characteristics because more Cr is distributed in the main phase particles as compared with the R-rich phase.

The details of the mechanism by which the temperature characteristics are improved are unknown. However, especially when Cr is contained only in the main phase particles and Cr is not contained in the R-rich phase, the temperature characteristics are particularly good. From this, it is considered that the temperature characteristics of the anisotropic magnetic field of the main phase particles are improved by containing Cr in the main phase particles.

On the other hand, when Cr is contained in the R-rich phase, the effect of improving the above temperature characteristics becomes small. Therefore, it is considered that the inclusion of Cr in the R-rich phase changes the magnetism of the R-rich phase and deteriorates the temperature characteristics.

A plurality of types of R-rich phases may be included as the grain boundary phase according to the present embodiment. Examples of the R-rich phase include the R ₆ T ₁₃ Ga phase, the R-Co-Cu-Ga phase, and the R-OC-N phase. When each of the above phases is included, the elements constituting each phase are contained in the RTB-based permanent magnet.

The R ₆ T ₁₃ Ga phase is a phase having a La ₆ Co ₁₁ Ga ₃ type crystal structure. Furthermore, the R ₆ T ₁₃ Ga phase is non-magnetic. The R ₆ T ₁₃ Ga phase has a Fe content of 30.00% by mass or more. The content of Ga is not particularly limited, but may be 3.00% by mass or more and 8.00% by mass or less.

By including the R ₆ T ₁₃ Ga phase in the grain boundaries, the magnetic separation between the main phase particles is increased, and Hcj is improved.

The Cr content in the R ₆ T ₁₃ Ga phase may be 0% by mass or more and less than 0.30% by mass, or 0% by mass or more and 0.03% by mass or less. That is, the R ₆ T ₁₃ Ga phase does not have to contain Cr.

The R-Co-Cu-Ga phase is a phase in which the Fe content is less than 30.00% by mass and the total content of Co, Cu and Ga is 2.00% by mass or more.

The Cr content in the R—Co—Cu—Ga phase may be 0% by mass or more and less than 0.20% by mass, or 0% by mass or more and 0.05% by mass or less. That is, the R—Co—Cu—Ga phase does not have to contain Cr.

The RO-C-N phase is a phase in which the total content of O, C and N with respect to the content of R is 0.05 or more and 0.20 by mass ratio.

The Cr content in the R—O—C—N phase may be 0% by mass or more and less than 0.05% by mass, or 0% by mass or more and 0.005% by mass or less. That is, the ROC-N phase does not have to contain Cr.

Further, the RTB-based permanent magnet according to the present embodiment may include an M1-B phase and / or an M1-C phase. In particular, it is preferable to include a Zr-B phase and / or a Zr-C phase.

Both the Zr-B phase and the Zr-C phase are precipitated around the main phase particles during the production of the RTB-based permanent magnets, and suppress the grain growth of the main phase particles. Then, the particle size of the main phase particles is reduced. The smaller the particle size of the main phase particles, the better the Hcj, and the better the temperature characteristics, especially the temperature characteristics of Hcj.

The Zr-B phase may be mainly a ZrB _two phase. ZrB ₂ phase is a phase having a crystal structure of hexagonal AlB ₂ type, deposited in a plate shape. In this case, the effect of suppressing the grain growth of the main phase particles becomes large.

The Zr-C phase may be mainly the ZrC phase. The ZrC phase is a phase having a face-centered cubic structure (NaCl structure) crystal structure, and precipitates in a cubic shape. In this case, the effect of suppressing the grain growth of the main phase particles becomes large.

Of the ZrB ₂ phase and the ZrC phase, the ZrB ₂ phase has a greater effect of suppressing the grain growth of the main phase particles.

Further, the RTB-based permanent magnet according to the present embodiment may or may not contain Ti, Hf, Nb, V, Mo and / or W, if necessary. Similar to Zr, these elements can also precipitate M1-B phase and / or M1-C phase at the grain boundaries, and have the effect of suppressing the grain growth of the main phase particles.

There is no particular limitation on the method for discriminating each phase contained in the main phase particles and the grain boundaries. For example, it can be discriminated by SEM, EPMA, TEM, or the like. FIG. 1 illustrates an SEM image of the RTB-based permanent magnet 1 according to the present embodiment. Note that FIG. 1 is an SEM image of Example 2 described later. In FIG. 1, the RTB-based permanent magnet 1 includes the main phase particles 11 and grain boundaries. The grain boundaries include R ₆ T ₁₃ Ga phase 13, R-Co-Cu-Ga phase 15, R-OC-N phase 19, and Zr-C phase 17. The method for measuring the composition of the main phase particles and each phase contained in the grain boundaries is not particularly limited. For example, it can be measured by EPMA or the like.

As can be seen from FIG. 1, in the SEM image, the R-rich phase appears whiter than the main phase particles. Among the R-rich phases, the R ₆ T ₁₃ Ga phase 13 looks gray compared to the other R rich phases, and the R-Co-Cu-Ga phase 15 looks whiter than the R ₆ T ₁₃ Ga phase. The —O—C—N phase 19 has a color close to that of the R—Co—Cu—Ga phase 15, but has a more rounded shape than the other R-rich phases. The Zr-C phase 17 is blacker than the R-rich phase and has a shape close to a square.

In FIG. 1, the Zr-B phase was not observed. However, as described above, the RTB-based permanent magnet according to the present embodiment may include the Zr-B phase. In the presence of the Zr-B phase, the Zr-B phase tends to have an elongated rectangular or needle-like shape. And, as compared with Zr-C phase 19, it is more likely to exist at the two-particle boundary.

Hereinafter, the composition of the RTB-based permanent magnet according to the present embodiment will be described.

In the RTB-based permanent magnet according to the present embodiment, R is one or more selected from rare earth elements. Rare earth elements are Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. In this embodiment, Sc is not included in the rare earth elements.

In the RTB-based permanent magnet according to the present embodiment, T may be Fe alone or Fe and Co.

In the RTB-based permanent magnet according to the present embodiment, B is boron.

The RTB-based permanent magnet according to the present embodiment further contains Cr.

The RTB-based permanent magnet according to the present embodiment may further contain Ga, M1 and M2. M1 is one or more selected from Zr, Ti, Hf, Nb, V, Mo and W, and M2 is one or more selected from Cu and Al.

The total content of R in the RTB-based permanent magnets according to the present embodiment is 28.00% by mass or more and 34.00% by mass or less, assuming that the entire RTB-based permanent magnets are 100% by mass. It may be 29.50 mass% or more and 33.00 mass% or less. If the total content of R is too low, the formation of main phase particles will be insufficient. Therefore, α-Fe having soft magnetism is likely to be deposited, and the square shape is likely to be deteriorated. Further, when the total content of R is too large, the volume ratio of the main phase particles tends to decrease, and the residual magnetic flux density (Br) tends to decrease.

Further, the total content of R may be the total content of Nd and Pr.

The total content of Nd and Pr may be 28.00% by mass or more and 34.00% by mass or less, and 29.50% by mass or more and 33.00% by mass or less.

The total content of Dy, Tb and Ho is not particularly limited. The total content of Dy, Tb and Ho may be 0.50% by mass or less (including 0% by mass). It may be substantially free of Dy, Tb and Ho. The fact that Dy, Tb and Ho are not substantially contained means that the total content of Dy, Tb and Ho is less than 0.10% by mass, specifically, assuming that the entire RTB-based permanent magnet is 100% by mass (100% by mass). (Including 0% by mass).

The content of B in the RTB-based permanent magnet according to the present embodiment may be 0.70% by mass or more and 0.95% by mass or less. It may be 0.80 mass% or more and 0.90 mass% or less. If the content of B is too small, α-Fe having soft magnetism is likely to be precipitated, and the square shape is likely to be deteriorated. If the content of B is too large, T will be used too much for the formation of the main phase particles, and T will be insufficient. As a result, the R ₆ T ₁₃ Ga phase is less likely to occur at the grain boundaries, and the Hcj of the R-TB system permanent magnet is likely to decrease.

The Co content in the RTB-based permanent magnet according to the present embodiment may be 0.30% by mass or more and 3.00% by mass or less. It may be 0.50% by mass or more and 2.00% by mass or less. When the Co content is suitable, the temperature characteristics, particularly the temperature characteristics of Br, are improved. Furthermore, corrosion resistance is improved. If the amount of Co is too small, the corrosion resistance and temperature characteristics, particularly the temperature characteristics of Br, deteriorate. Further, if the amount of Co is too small, the square shape of the RTB-based permanent magnet may deteriorate. On the other hand, since Co is an expensive metal, the cost increases as the amount added increases. The Co content is determined in consideration of these factors.

The Fe content is a substantial balance of the RTB-based permanent magnets. The substantial balance means the balance excluding other elements described later.

The Cr content may be 0.05% by mass or more and 0.50% by mass or less. It is preferably 0.10% by mass or more and 0.30% by mass or less. Cr preferentially dissolves in the main phase particles and then in the grain boundary phase (R-rich phase). When the Cr content is within the above range, Cr is likely to be contained only in the main phase particles, and the temperature characteristics of the RTB-based permanent magnet are likely to be improved. If the Cr content is too low, the main phase particles do not contain enough Cr. If the content of Cr is too large, Cr is likely to be contained in the R-rich phase as well.

The content of Ga may be 0.30% by mass or more and 1.00% by mass or less. It may be 0.40 mass% or more and 0.80 mass% or less. If the Ga content is too low, Hcj tends to decrease. If the Ga content is too high, Br tends to decrease.

The total content of M1 may be 0.10% by mass or more and 3.00% by mass or less.

The content of Zr, which is a kind of M1, may be 0.10% by mass or more and 1.50% by mass or less. It may be 0.20 mass% or more and 1.00 mass% or less. As described above, when Zr is contained, the Zr-B phase and / or the Zr-C phase can be precipitated at the grain boundaries. The inclusion of the Zr-B phase and / or the Zr-C phase in the grain boundaries suppresses the grain growth of the main phase particles. Then, it becomes easy to improve the square shape and Hcj. If the content of Zr is too large, the volume ratio of the main phase particles decreases, and Br tends to decrease.

Further, if necessary, Ti, Hf, Nb, V, Mo and / or W which are M1 other than Zr may be contained. Similar to Zr, these elements can also precipitate M1-B phase and / or M1-C phase at the grain boundaries, and have the effect of suppressing the grain growth of the main phase particles.

The total content of M2 may be greater than 0% by mass and less than or equal to 2.00% by mass.

Cu may be contained if necessary. The Cu content may be 0.05% by mass or more and 0.80% by mass or less, or 0.10% by mass or more and 0.40% by mass or less. By containing Cu, Hcj and corrosion resistance can be easily improved. However, if the Cu content is too high, Br tends to decrease.

Al may be contained if necessary. The Al content may be 0.07% by mass or more and 0.60% by mass or less. Hcj can be easily improved by containing Al. However, if the Al content is too high, Br tends to decrease. Further, the temperature characteristic of Br tends to decrease.

The RTB-based permanent magnet according to the present embodiment may contain elements other than the above-mentioned R, T, B, Cr, Ga, M1 and M2 as other elements. The content of other elements is not particularly limited. For example, assuming that the total mass of the RTB-based permanent magnets is 100% by mass, the total mass may be 2.00% by mass or less, or 0.60% by mass or less.

Hereinafter, the contents of carbon (C), nitrogen (N) and oxygen (O) will be described as an example of other elements.

The content of C in the RTB-based permanent magnet according to the present embodiment may be 0.03% by mass or more and 0.20% by mass or less. There is no particular limitation on the method for controlling the C content. For example, the content of C can be controlled by controlling the type of the raw material metal, the type and amount of the pulverizing aid, and the type and amount of the molding aid.

The content of O in the RTB-based permanent magnet according to the present embodiment may be 0.03% by mass or more and 0.20% by mass or less. There is no particular limitation on the method of controlling the O content. For example, the content of O can be controlled by controlling the amount of oxygen in the atmosphere at the time of production.

The content of N in the RTB-based permanent magnet according to the present embodiment is 0.01 mass, where 100 parts by mass is the total of the elements other than O, C and N in the RTB-based permanent magnet. It may be% or more and 0.20 mass% or less. There is no particular limitation on the method for controlling the N content.

As a method for measuring various components contained in the RTB-based permanent magnet according to the present embodiment, a conventionally known method can be used. The amounts of various elements are measured by, for example, a fluorescent X-ray analysis method, an inductively coupled plasma emission spectroscopic analysis method (ICP method), or the like. The O content is measured, for example, by the Inert Gas Melting-Non-Dispersive Infrared Absorption Method. The C content is measured, for example, by the combustion in oxygen stream-infrared absorption method. The N content is measured, for example, by the Inert Gas Melting-Thermal Conductivity method.

The RTB-based permanent magnet according to the present embodiment is generally processed into an arbitrary shape and used. The shape of the RTB-based permanent magnet according to the present embodiment is not particularly limited, and for example, a rectangular parallelepiped, a hexahedron, a flat plate, a columnar shape such as a quadrangular prism, or a cross-sectional shape of the RTB-based permanent magnet. Can have any shape such as a C-shaped cylinder. The quadrangular prism may be, for example, a quadrangular prism having a rectangular bottom surface and a square quadrangular prism having a square bottom surface.

Further, the RTB-based permanent magnet according to the present embodiment includes both a magnet product obtained by processing and magnetizing the magnet and a magnet product not magnetizing the magnet.

<Manufacturing method of RTB system permanent magnet>
Hereinafter, a method for producing an RTB-based sintered magnet will be described as an example of a method for producing an RTB-based permanent magnet according to the present embodiment. The method for manufacturing the RTB-based permanent magnet according to the present embodiment is not particularly limited. For example, it has the following steps.

(A) Alloy manufacturing process for producing an alloy for RTB-based permanent magnets (raw material alloy) (b) Crushing process for crushing the raw material alloy (c) Molding process for molding the obtained alloy powder (d) Molding Sintering step of sintering the body to obtain RTB-based permanent magnets (e) Aging treatment step of aging RTB-based permanent magnets (f) Processing RTB-based permanent magnets Processing process

[Alloy manufacturing process]
First, an alloy for RTB-based permanent magnets according to this embodiment is produced (alloy production step). Hereinafter, the strip casting method will be described as an example of the alloy manufacturing method, but the alloy manufacturing method is not limited to the strip casting method.

First, a raw metal corresponding to the composition of the RTB-based permanent magnet alloy according to the present embodiment is prepared, and the prepared raw metal is dissolved in a vacuum or an atmosphere of an inert gas such as Ar gas. Then, the molten raw material metal is poured into the rotating metal roll surface to produce the RTB-based permanent magnet alloy (raw material alloy) according to the present embodiment. In this embodiment, a one-alloy method in which one type of raw material alloy is produced and crushed to produce a raw material powder will be described, but two types of raw material alloys, a first alloy and a second alloy, are produced. , A two-alloy method may be used in which the raw material powder is produced by mixing after crushing each of them.

There are no particular restrictions on the type of raw material metal. For example, rare earth metals or rare earth alloys, iron, cobalt, ferrobolon, and alloys and compounds thereof can be used. There is no particular limitation on the casting method for casting the raw material metal. If the obtained raw material alloy has solidification segregation, it may be homogenized (solubilized) as necessary.

[Crushing process]
After producing the raw material alloy, the raw material alloy is crushed (crushing step). The pulverization step may be performed in two steps, a coarse pulverization step of pulverizing until the particle size is about several hundred μm to several mm, and a fine pulverization step of pulverizing until the particle size is about several μm. It may be performed in one step of only the fine pulverization step.

(Coarse crushing process)
The raw material alloy is roughly pulverized until the particle size is about several hundred μm to several mm (coarse pulverization step). As a result, a coarsely pulverized powder of the raw material alloy is obtained. Coarse pulverization can be performed, for example, by occluding hydrogen in a raw material alloy to cause self-destructive pulverization (hydrogen storage pulverization).

The method of coarse pulverization is not limited to the above hydrogen storage pulverization. For example, coarse crushing may be performed using a coarse crusher such as a stamp mill, a jaw crusher, or a brown mill in an inert gas atmosphere.

Further, in order to obtain an RTB-based permanent magnet having high magnetic characteristics, the atmosphere of each step from the rough pulverization step to the sintering step described later may be an atmosphere of low oxygen concentration. The oxygen concentration is adjusted by controlling the atmosphere in each manufacturing process. For example, each step is preferably carried out in an atmosphere having an oxygen concentration of 100 ppm or less.

(Fine crushing process)
After the raw material alloy is coarsely pulverized, the obtained coarsely pulverized powder is finely pulverized until the average particle size becomes about several μm (fine pulverization step). As a result, a finely pulverized powder of the raw material alloy is obtained. A finely pulverized powder can be obtained by further pulverizing the coarsely pulverized powder. The D50 of the particles contained in the finely pulverized powder is not particularly limited. For example, D50 may be 1.0 μm or more and 5.0 μm or less, or 2.5 μm or more and 3.5 μm or less. The smaller the D50, the easier it is to improve the Hcj of the RTB-based permanent magnet according to the present embodiment. However, abnormal grains are likely to be formed in the sintering process. The larger the D50, the more difficult it is for abnormal grains to be formed in the sintering process. However, the Hcj of the RTB-based permanent magnet according to the present embodiment tends to decrease.

Fine pulverization is carried out by further pulverizing the coarsely pulverized powder using a fine pulverizer such as a jet mill, a ball mill, a vibration mill, or a wet attritor while appropriately adjusting conditions such as pulverization time. .. The jet mill will be described below. Jet mill, high-pressure inert gas (e.g., He gas, N ₂ gas, Ar gas) is opened narrower nozzle to generate a high speed gas flow, the coarsely pulverized powder material alloy by the high-velocity gas stream It is a fine pulverizer that accelerates and causes collisions between coarsely pulverized powders of raw material alloys and collisions with targets or container walls to pulverize them.

When the coarsely pulverized powder of the raw material alloy is finely pulverized, a pulverizing aid may be added. There are no particular restrictions on the type of crushing aid. For example, an organic lubricant or a solid lubricant may be used. Examples of the organic lubricant include oleic acid amide, lauric acid amide, zinc stearate and the like. Examples of the solid lubricant include boron nitride and graphite. By adding the pulverizing aid, it is possible to obtain a finely pulverized powder that easily orients when a magnetic field is applied in the molding step. Only one of the organic lubricant and the solid lubricant may be used, or both may be mixed and used.

[Molding process]
The finely pulverized powder is molded into a desired shape (molding process). In the molding step, the finely pulverized powder is filled in a mold arranged in an electromagnet and pressurized to form the finely pulverized powder to obtain a molded product having a desired shape. At this time, by molding while applying a magnetic field, the crystal axis of the finely pulverized powder can be molded in a state of being oriented in a specific direction. Since the obtained molded product is oriented in a specific direction, an RTB-based permanent magnet having a stronger magnetization in the specific direction can be obtained. Moreover, you may add a molding aid. The type of the molding aid is not particularly limited, and the same lubricant as the pulverizing aid may be used. Further, the pulverizing aid may also serve as a molding aid.

The pressure at the time of pressurization may be, for example, 30 MPa or more and 300 MPa or less. The magnetic field to be applied may be, for example, 1000 kA / m or more and 1600 kA / m or less. The applied magnetic field is not limited to the static magnetic field, and may be a pulsed magnetic field. Further, a static magnetic field and a pulsed magnetic field can be used in combination.

As a molding method, in addition to dry molding in which the finely pulverized powder is molded as it is as described above, wet molding in which a slurry in which the finely pulverized powder is dispersed in a solvent such as oil can be applied.

The shape of the molded product obtained by molding the finely pulverized powder is not particularly limited, and depends on the desired shape of the RTB-based permanent magnet, such as a rectangular parallelepiped, a flat plate, a columnar shape, or a ring shape. It can be shaped.

[Sintering process]
The obtained molded product is sintered in a vacuum or an inert gas atmosphere to obtain an RTB-based permanent magnet (sintering step). The holding temperature at the time of sintering needs to be adjusted according to various conditions such as composition, pulverization method, difference in particle size and particle size distribution. The holding temperature is not particularly limited, but may be, for example, 950 ° C. or higher and 1150 ° C. or lower. The holding time is not particularly limited, but may be, for example, 1 hour or more and 24 hours or less. The shorter the holding time, the higher the production efficiency. There is no particular limitation on the atmosphere during holding. For example, it may be an inert gas atmosphere or a vacuum atmosphere of less than 100 Pa. By sintering, the RTB-based permanent magnet according to the present embodiment can be obtained.

[Aging process]
After the compact is sintered, the RTB permanent magnets are aged (aging treatment step). After sintering, the RTB-based permanent magnets are subjected to aging treatment by holding the obtained RTB-based permanent magnets at a temperature lower than that at the time of sintering. Hereinafter, the case where the aging process is divided into two stages of the first aging process and the second aging process will be described, but the first aging process may be omitted and only the second aging process may be performed.

There are no particular restrictions on the holding temperature and holding time in each aging treatment. For example, the first aging treatment may be performed at a holding temperature of 800 ° C. or higher and 1000 ° C. or lower for 1 hour or more and 4 hours or less. The atmosphere during the first aging treatment may be an inert gas atmosphere (for example, He gas, Ar gas) having a pressure equal to or higher than atmospheric pressure. The second aging treatment may be carried out at a holding temperature of 450 ° C. or higher and 550 ° C. or lower for 30 minutes or longer and 4 hours or shorter. The atmosphere during the second aging treatment may be an inert gas atmosphere having a pressure equal to or higher than atmospheric pressure (for example, He gas or Ar gas). In particular, the second aging treatment makes it easier to make the Cr content in the R-rich phase contained in the grain boundaries of the R-TB permanent magnets smaller than the Cr content in the main phase particles, and R- It becomes easy to improve the Hcj of the TB-based permanent magnet. When the holding temperature of the second aging treatment is out of the above range, the Cr content in the R-rich phase tends to be larger than the Cr content in the main phase particles. Further, the aging treatment step may be performed after the processing step described later.

[Processing process]
The obtained RTB-based permanent magnet may be processed into a desired shape as needed (processing step). Examples of the processing method include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing. The processing step may be omitted.

The RTB-based permanent magnets obtained by the above method may be subjected to surface treatment such as plating, resin coating, oxidation treatment, or chemical conversion treatment in order to improve various properties such as corrosion resistance. Thereby, the corrosion resistance can be further improved.

The RTB-based permanent magnet according to the present embodiment obtained as described above has good magnetic characteristics and improved temperature characteristics. In particular, the temperature characteristics of Hcj are improved, and the absolute value of the temperature coefficient of Hcj is reduced. If the temperature characteristics of Hcj are improved, even if Hcj at room temperature is low, high Hcj can be obtained when used at high temperature. That is, it becomes easy to reduce the amounts of Dy, Tb and Ho, which have a large effect of improving Hcj at room temperature. Here, Dy, Tb and Ho are highly ubiquitous in the region and are expensive. Therefore, if the temperature characteristics of Hcj are improved, the cost and supply risk can be reduced.

The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention. For example, the RTB-based permanent magnet according to the present embodiment may be manufactured by hot working.

The application of the RTB-based permanent magnet of the present invention is not particularly limited. In particular, it is suitably used for applications exposed to high temperatures during use, for example, magnets for automobiles and magnets for air conditioners.

Hereinafter, the invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Alloy manufacturing process)
In the alloy manufacturing process, first, a raw material metal having a predetermined element was prepared. As the raw material metal, a simple substance of the element shown in Table 1 or a compound such as an alloy containing the element shown in Table 1 was appropriately selected and prepared. The TRE in Table 1 is the total content of R. Further, in this embodiment, the elements not listed in Table 1 are not contained in excess of the amount of impurities. Then, in each of the Examples and Comparative Examples of Table 1, the total content of the other elements is 0.60% by mass or less.

Next, these raw material metals are weighed so that the finally obtained RTB-based permanent magnets have the compositions shown in each of the examples and comparative examples in Table 1, and a raw material alloy is prepared by a strip casting method. did.

(Crushing process)
In the crushing step, the raw material alloy obtained in the alloy manufacturing step was crushed to obtain an alloy powder. The pulverization was performed in two stages of coarse pulverization and fine pulverization. Rough pulverization was performed by hydrogen storage pulverization. Specifically, the raw material alloy was occluded with hydrogen at room temperature, and then dehydrogenated at 600 ° C. for 1 hour in an Ar flow atmosphere.

Each step (fine pulverization and molding) from rough pulverization to sintering was performed in an N ₂ atmosphere having an oxygen concentration of less than 50 ppm.

Lauric acid amide was added as a pulverization aid to the alloy powder obtained by coarse pulverization. The amount added was 0.10 parts by mass with respect to 100 parts by mass of the alloy powder, and the mixture was mixed after the addition of the pulverizing aid. Then, fine pulverization was performed using a jet mill. N ₂ gas was used in the jet mill. Fine pulverization was carried out until the D50 of the alloy powder became about 3.0 μm.

(Molding process)
In the molding step, the alloy powder obtained in the pulverization step was molded in a magnetic field to obtain a molded product. After the alloy powder was filled in a mold arranged in an electromagnet, it was formed by pressurizing it while applying a magnetic field by the electromagnet. The magnitude of the applied magnetic field was 1600 kA / m. The pressure at the time of molding was 100 MPa.

(Sintering process)
In the sintering step, the obtained molded product was sintered to obtain a sintered body. The holding temperature at the time of sintering was 1070 ° C., and the holding time was 5 hours. The atmosphere at the time of sintering was a vacuum atmosphere of 10 Pa.

(Aging process)
In the aging step, the obtained sintered body was subjected to aging treatment to obtain an RTB-based permanent magnet. The aging process was performed in two stages, the first aging process and the second aging process.

In the first aging treatment, the holding temperature was 900 ° C. and the holding time was 1 hour. The atmosphere during the first aging treatment was an Ar atmosphere.

In the second aging treatment, the holding temperature and holding time shown in Table 2 were used. The atmosphere during the second aging treatment was an Ar atmosphere.

It was confirmed by the composition analysis by the fluorescent X-ray analysis method, the ICP method, and various gas analysis methods that the composition of the raw material alloy in each Example and Comparative Example was the composition shown in Table 1. Specifically, elements other than B, C, O and N were measured by fluorescent X-ray analysis, the content of B was measured by ICP, and the content of C was measured by combustion in oxygen stream-infrared absorption method. The content of O was measured by the Inert gas melting-non-dispersion infrared absorption method. The N content was measured by the Inert Gas Melting-Thermal Conductivity Method.

The obtained sintered body was processed into a shape for measuring magnetic characteristics with a BH curve tracer (TRF manufactured by Toei Kogyo Co., Ltd.), and the magnetic characteristics were measured with a BH curve tracer. The measurement of the magnetic characteristics was carried out at 23 ° C. and 150 ° C. by controlling the temperature of the magnetic poles of the BH curve tracer. Then, the temperature coefficient of Hcj was calculated. The results are shown in Table 2.

Further, in Examples 1 to 4 and Comparative Examples 1 and 2, the cross sections of the obtained RTB-based permanent magnets were observed using an SEM at a magnification of 5000 times. As a result, the grain boundaries contained the R-rich phase in all the examples and comparative examples. Furthermore, using SEM and EPMA at the grain boundaries of each Example and Comparative Example, R ₆ T ₁₃ Ga phase, R-Co-Cu-Ga phase, R-OC-N phase, Zr-B phase and Zr- It was observed whether or not the C phase was contained. The results are shown in Table 2. Note that FIG. 1 is an SEM image of Example 2.

Furthermore, in Examples 1 to 4 containing Cr, it was confirmed by using EPMA that the content of Cr in the main phase particles was higher than the content of Cr in the R-rich phase. Specifically, when one analysis point is set for each of the three different main phase particles and the R ₆ T ₁₃ Ga phase, the R-Co-Cu-Ga phase, and the R-OC-N phase are present. 3 analysis points were set for each, and the composition was analyzed by EPMA. Then, the Cr content was compared at each analysis point.

In each example, the Cr content was higher at all analysis points in the main phase particles than at all analysis points in the R-rich phase. On the other hand, Comparative Example 1 did not contain Cr. Further, in Comparative Example 2, the Cr content at the analysis point of the main phase particles was lower than the Cr content at the analysis point of the R-rich phase because the second aging temperature was too high. In particular, Table 3 shows the results of EPMA analysis in Comparative Example 1, Example 2, and Example 4.

From Tables 1 to 3, Examples 1 to 4 in which the main phase particles have a higher Cr content than the R-rich phase have a smaller absolute value of the temperature coefficient of Hcj than Comparative Example 1 containing no Cr. , The temperature characteristics were excellent.

Further, in Comparative Example 2 in which the Cr content at the analysis point of the main phase particles is lower than the Cr content at the analysis point of the R-rich phase, the conditions are substantially the same except for the holding temperature and holding time of the second aging treatment. Hcj was significantly reduced as compared with Example 2 carried out in. Furthermore, the absolute value of the temperature coefficient of Hcj was larger than that of Comparative Example 1 containing no Cr.

1 R-TB system permanent magnet 11 Main phase particles 13 R ₆ T ₁₃ Ga phase 15 R-Co-Cu-Ga phase 17 Zr-C phase 19 R-OC-N phase

Claims (7)

An RTB-based permanent magnet containing Cr.
R is one or more selected from rare earth elements, T is Fe alone or Fe and Co, and B is boron.
The RTB-based permanent magnet includes a main phase particle and a grain boundary phase existing at a grain boundary.
An R-rich phase is included as the grain boundary phase,
An RTB-based permanent magnet characterized in that the main phase particles have a higher Cr content than the R-rich phase. The RTB-based permanent magnet according to claim 1, which comprises one or more selected from Nd and Pr as R. It also contains Ga
The R-rich phase includes the R ₆ T ₁₃ Ga phase.
The RTB-based permanent magnet according to claim 1 or 2, wherein the Cr content in the R ₆ T ₁₃ Ga phase is 0% by mass or more and less than 0.30% by mass. T is Fe and Co, and further contains Ga and Cu,
The R-rich phase contains an R-Co-Cu-Ga phase.
The RTB-based permanent magnet according to any one of claims 1 to 3, wherein the Cr content in the R-Co-Cu-Ga phase is 0% by mass or more and less than 0.20% by mass. It also contains Zr and
The RTB-based permanent magnet according to any one of claims 1 to 4, further comprising a Zr-B phase and / or a Zr-C phase as the grain boundary phase. T is Fe and Co, and further contains Ga, M1 and M2.
M1 is one or more selected from Zr, Ti, Hf, Nb, V, Mo, and W and contains at least Zr.
M2 is one or more selected from Cu and Al.
Taking the entire RTB-based permanent magnet as 100% by mass,
The total content of R is 28.00% by mass or more and 34.00% by mass or less,
Co content is 0.30% by mass or more and 3.00% by mass or less,
B content is 0.70% by mass or more and 0.95% by mass or less,
Cr content is 0.05% by mass or more and 0.50% by mass or less,
Ga content is 0.30% by mass or more and 1.00% by mass or less,
The total content of M1 is 0.10% by mass or more and 3.00% by mass or less,
Zr content is 0.10% by mass or more and 1.50% by mass or less,
The total content of M2 is greater than 0% by mass and less than 2.00% by mass.
The RTB-based permanent magnet according to any one of claims 1 to 5, wherein Fe is a substantial balance. The RTB-based permanent magnet according to claim 6, wherein the total content of R is the total content of Nd and Pr.

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