JP2022152420A - R-t-b based permanent magnet and method of producing the same - Google Patents

Abstract

To provide an R-T-B based permanent magnet having both high residual magnetic flux density and high coercive force, and a method for producing the R-T-B based permanent magnet.SOLUTION: A method for producing an R-T-B based permanent magnet includes: a step of preparing a magnet base material 20 including an R-T-B based alloy; a first diffusion step of attaching a first diffusion material sheet 11a, which is formed by mixing a binder and a first diffusion material 11 containing a light rare earth element, to at least part of a surface of the magnet base material and then heating the magnet base material 20 with the first diffusion material 11 attached thereon; and a second diffusion step of, after the first diffusion step, attaching a second diffusion material sheet 12a, which is sheeted by mixing a binder and a second diffusion material 12 containing a heavy rare earth element, to at least part of a surface of the magnet base material and then heating the magnet base material 20 with the second diffusion material 12 attached thereon.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a method of producing an RTB permanent magnet through a grain boundary diffusion process, and an RTB permanent magnet produced by the method.

Rare earth magnets having RTB-based compositions have magnetic properties superior to those of other permanent magnets, and in recent years, various studies have been made with the aim of further improving their magnetic properties. For example, in Patent Document 1, a method of fabricating an RTB system permanent magnet, attaching a heavy rare earth element to the surface and heating the magnet to diffuse the heavy rare earth element through grain boundaries (grain boundary diffusion method). is disclosed. Magnetic properties, particularly coercive force, can be improved by using this method.

However, today, many magnetic parts (motors, etc.) are required to be smaller, lighter, higher performance, and more efficient. It is necessary to improve both the residual magnetic flux density and the coercive force of the system permanent magnet.

WO2016/121790

The present invention has been made in view of the above circumstances, and an object of the present invention is to produce an RTB system permanent magnet having both a high residual magnetic flux density and a high coercive force, and the RTB system permanent magnet. to provide a method.

In order to achieve the above object, a method for producing an RTB permanent magnet according to the present invention comprises:
preparing a magnet base material containing an RTB alloy;
a first diffusing step of attaching a first diffusing material containing at least one light rare earth element to at least a part of the surface of the magnet base material, and heating the magnet base material to which the first diffusing material is attached;
After the first diffusion step, a second diffusing material containing at least one heavy rare earth element is attached to the surface of at least a part of the magnet base material, and the magnet base material with the second diffusing material attached thereto and a second diffusion step of heating the

As described above, an RTB system permanent magnet having both high residual magnetic flux density and high coercive force is produced by carrying out two-step grain boundary diffusion in which light rare earth elements are diffused and then heavy rare earth elements are diffused. can get.

Preferably, the first diffusing material contains at least one element selected from the group consisting of Nd and Pr as the light rare earth element.

Further, preferably, the first diffusing material includes an RL-M alloy containing the light rare earth element and M, and in the RL-M alloy, RL is the light rare earth element, and M is RL is an element whose eutectic temperature with is 800° C. or less.

Also, preferably, the content of the heavy rare earth element in the first diffusing material is 10% by mass or less, and more preferably, the first diffusing material does not substantially contain the heavy rare earth element.

On the other hand, the second diffusing material preferably contains at least one element selected from the group consisting of Tb and Dy as the heavy rare earth element.

Preferably, the RTB-based alloy contained in the magnet base material contains one or more rare earth elements essentially including Nd as R and one or more iron group elements essentially including Fe as T. , boron, and Cu. And preferably, in the RTB alloy, the total content of R is 27.5% by mass or more and 30.8% by mass or less, and the content of Cu is 0.05% by mass or more. , 0.5% by mass or less, and the content of B is 0.92% by mass or more and 1.03% by mass or less.
When the magnet base material satisfies the above composition, the effect of improving the residual magnetic flux density and the coercive force becomes more remarkable.

The RTB system permanent magnet according to the present invention can be obtained, for example, by the manufacturing method described above,
RT wherein R is one or more light rare earth elements and one or more heavy rare earth elements consisting essentially of Nd, T is one or more iron group elements consisting essentially of Fe, and B is boron - a B-based permanent magnet,
The RTB permanent magnet contains a plurality of core-shell particles,
Each of the plurality of core-shell particles has a core portion containing R ₂ T ₁₄ B crystals and a shell portion covering the core portion and having a higher content ratio of the heavy rare earth element than the core portion. ,
In a cross section at a depth of 100 μm from the surface of the RTB permanent magnet, the average maximum thickness of the shell portion is 0.5 μm or less,
R-- having a concentration distribution in which both the content of the light rare earth element and the content of the heavy rare earth element decrease in the depth direction from the surface of the RTB permanent magnet. TB system permanent magnet.

Since the RTB system permanent magnet has the above characteristics, it is possible to improve both the residual magnetic flux density and the coercive force.

Preferably, the RTB-based permanent magnet of the present invention contains element M whose eutectic temperature with the light rare earth element is 800° C. or less,
The RTB permanent magnet has a concentration distribution in which the content of the element M decreases from the surface toward the depth direction.

Preferably, the RTB permanent magnet further contains Cu, the total R content is 28.4% by mass or more and 32.0% by mass or less, and the Cu content is , 0.2% by mass or more and 0.7% by mass or less, and the content of B is 0.92% by mass or more and 1.03% by mass or less.
When the RTB system permanent magnet satisfies the above composition, magnetic properties (especially coercive force) are further improved.

Preferably, the heavy rare earth element contained in the RTB system permanent magnet is Tb and/or Dy. Preferably, the RTB system permanent magnet further contains Pr as the light rare earth element.

The RTB system permanent magnet preferably has a residual magnetic flux density of 1450 mT or more and a coercive force of 1800 kA/m or more.

The RTB system permanent magnet of the present invention can be used as a component of motors, generators, compressors, actuators, magnetic sensors, speakers, etc., and is particularly suitable as a component of motors. In addition, the motor containing the RTB permanent magnet of the present invention can be mounted on various electronic devices and industrial devices, and is particularly suitable for use as a motor for automobiles (EV, HV, PHV, etc.). is.

FIG. 1 is a perspective view showing an example of a magnet base material. FIG. 2 is a schematic diagram schematically showing the flow of the first and second diffusion steps. FIG. 3A is a cross-sectional schematic diagram showing an enlarged cross section of the magnet base material. FIG. 3B is a schematic cross-sectional view showing an enlarged cross-section of the RTB system permanent magnet after the second diffusion step. FIG. 4A is a perspective view showing an example of an RTB system permanent magnet. FIG. 4B is a cross-sectional view along line VB-VB shown in FIG. 4A. FIG. 5 is a schematic diagram showing a cross section of a core-shell particle. FIG. 6 is an SEM cross-sectional photograph of an RTB system permanent magnet according to Example (Sample 1). FIG. 7 is an SEM cross-sectional photograph of the RTB system permanent magnet according to Comparative Example 1. FIG. FIG. 8 is a schematic diagram of an IPM motor using RTB system permanent magnets of the present invention. FIG. 9 is a schematic diagram showing an automobile using the IPM motor shown in FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

In this embodiment, first, a method for manufacturing an RTB system permanent magnet will be described, and then the characteristics of the RTB system permanent magnet obtained by this manufacturing method will be described. The method for producing an RTB permanent magnet according to the present embodiment includes steps of preparing a magnet base material, a first diffusion step of diffusing a light rare earth element into the magnet base material, and and a second diffusion step of further diffusing the heavy rare earth element into the material. Each step will be described below in order.

(Preparation step for magnet base material)
In this step, the magnet base material 20 shown in FIG. 1 is manufactured. First, the features of the magnet base material 20 will be described in detail. The magnet base material 20 is a sintered body of an RTB-based alloy, and is a material before performing the diffusion process described later. In FIG. 1, the magnet base 20 is a rectangular parallelepiped having two main surfaces 20a perpendicular to the Z-axis and four side surfaces 20b perpendicular to the X-axis or the Y-axis. However, the shape of the magnet base material 20 is not particularly limited, and may be, for example, a polygonal shape, a cylindrical shape, a hollow cylindrical shape, or an arc segment shape whose main surface is curved in an arc shape. In the drawings, the X-axis, Y-axis, and Z-axis are substantially perpendicular to each other.

In this embodiment, the two main surfaces 20a of the magnet base material 20 are used as magnetic pole surfaces. A magnetic pole surface is a surface through which magnetic flux mainly passes, and is a positive electrode (N pole) or a negative electrode (S pole) of a permanent magnet. When the RTB system permanent magnet to be manufactured is an anisotropic magnet, the magnetic pole faces can be determined by the direction of the magnetic field applied in the molding process, which will be described later. It should be noted that there is no particular limitation as to which surface of the magnet base material 20 is to be the magnetic pole surface. It can be a face.

In the RTB alloy forming the magnet base material 20, R is one or more rare earth elements essentially including Nd (neodymium), and T is one or more essentially Fe (iron). and B is boron. Here, the rare earth elements mean Sc, Y and lanthanoid elements belonging to Group 3 of the long period periodic table. They are called heavy rare earth elements (RH), and rare earth elements other than RH are called light rare earth elements (RL). Also, the iron group elements refer to Fe, Co, and Ni.

The total content of R contained in the magnet base material 20 can be 25% by mass to 35% by mass, preferably 27.5% by mass or more and 30.8% by mass or less. When the total content of R satisfies the above composition range, precipitation of α-Fe exhibiting soft magnetism is suppressed, and R ₂ T ₁₄ B crystals are more likely to be generated. Here, in the present embodiment, the "content rate of the predetermined element contained in the magnet base material 20" is the content rate per unit mass of the magnet base material 20, and the content of the predetermined element with respect to 100% by mass of the magnet base material. means ratio. That is, the above total R content is calculated as a ratio of the total mass of the rare earth elements to 100 mass % of the magnet base material. The content of a predetermined element in the permanent magnet 2, which will be described later, is also expressed in the same manner as above.

When a plurality of rare earth elements are included as R, the content of Nd included in the magnet base material 20 is not particularly limited, but is preferably 22% by mass or more. In this case, it is preferable that the magnet base material 20 contain Pr, Tb, and Dy as rare earth elements other than Nd. When a heavy rare earth element (RH) such as Tb or Dy is added as R other than Nd, the total content of RH contained in the magnet base material 20 is preferably 2.5% by mass or less.

The content of B contained in the magnet base material 20 can be 0.5% by mass to 1.5% by mass, preferably 0.92% by mass to 1.03% by mass.

On the other hand, the content of T contained in the magnet base material 20 is expressed as the balance, and may be appropriately determined according to the content of other elements. T may be Fe alone, or part of Fe may be substituted with Co. In this case, the Co content is not particularly limited, and can be, for example, 4% by mass or less, preferably 1% by mass or less.

In addition to R, T, and B described above, the magnet base material 20 preferably contains one or more m elements selected from the group consisting of Cu, Ga, Al, and Zr. As the m element, it is more preferable to contain Cu among the above.

The content of Cu contained in the magnet base material 20 is preferably 0.05% by mass or more and 0.50% by mass or less. In addition, when Ga, Al, and Zr are included as the m element, the content of these elements is not particularly limited. The Zr content is preferably 0.10 mass % or more and 0.30 mass % or less, and the Zr content is preferably 0.10 mass % or more and 0.30 mass % or less.

The magnet base material 20 may also contain carbon (C), nitrogen (N), and oxygen (O). The carbon content in the magnet base material 20 is preferably 1100 ppm by mass or less, more preferably 900 ppm by mass or less. The nitrogen content in the magnet base material 20 is preferably 1000 ppm by mass or less, more preferably 600 ppm by mass or less. The oxygen content in the magnet base material 20 is preferably 1200 ppm or less, more preferably 800 ppm or less.

Furthermore, the magnet base material 20 may contain unavoidable impurities such as Mn, Ca, Cl, S, and F in addition to the elements described above. It is about 1.0% by mass to 1.0% by mass.

The composition of the magnet base material 20 can be analyzed by a conventionally generally known method. For example, the contents of various elements such as R, T, and B can be measured by X-ray fluorescence spectroscopy (XRF) or inductively coupled plasma emission spectroscopy (ICP). Further, for example, the oxygen content can be measured by an inert gas fusion-nondispersive infrared absorption method, the carbon content can be measured by combustion in an oxygen stream-infrared absorption method, and the nitrogen content can be measured by an infrared absorption method. It can be measured by active gas fusion-thermal conductivity method.

As shown in FIG. 3A, the magnet base material 20 includes main phase grains 4 made of R ₂ T ₁₄ B crystals, grain boundaries 6 located between the main phase grains 4, and other magnetic properties. Secondary phases may be present to the extent that they are not harmful.

The average particle diameter of the main phase particles 4 is not particularly limited, and can be, for example, 1.0 μm to 10 μm, preferably 2.5 μm to 6.0 μm, in terms of circle equivalent diameter. Note that the average particle diameter of the main phase particles 4 is determined by observing the cross section of the magnet base material 20 as shown in FIG. It can be measured by measuring the equivalent circle diameter of the particles 4 .

In the R ₂ T ₁₄ B crystal forming the main phase particles 4, part of T, which is an iron group element, may be substituted with a transition metal element such as the m element.

The grain boundaries 6 include two grain boundaries 6a positioned between two adjacent main phase grains 4 and grain boundary multiple points 6b surrounded by three or more main phase grains 4. In addition, the grain boundaries 6 are composed of phases other than the main phase grains 4 (that is, phases other than the R ₂ T ₁₄ B crystal phase), and the types and proportions of the phases constituting the grain boundaries 6 are particularly limited. not. Other phases constituting the grain boundary 6 include, for example, a phase having a higher concentration of R than the main phase grains 4 (R-rich layer), a phase having a high concentration of transition metal elements such as T (iron group element) and Ga. , an oxide layer of a rare earth element, an R—O—C phase, and the like.

The magnet base material 20 having the characteristics described above is manufactured through a process of manufacturing a raw material alloy, a process of pulverizing the raw material alloy (pulverizing process), a process of molding the raw material alloy powder (forming process), and a process of sintering the compact. (Sintering step) and can be manufactured through.

First, raw metals corresponding to the composition of the RTB alloy described above are prepared, and the prepared raw metals are melted in a vacuum or an inert gas atmosphere such as Ar gas. After that, a raw material alloy is obtained by casting the melted raw material metal.

At this time, there is no particular limitation on the type of raw material metal, and for example, rare earth metals or rare earth alloys, pure iron, pure cobalt, ferroboron, and alloys and compounds thereof can be used. Also, the method of casting the raw material metal is not particularly limited, and examples thereof include an ingot casting method, a strip casting method, a book mold method, or a centrifugal casting method. Further, if the raw material alloy after casting has solidification segregation, it may be subjected to homogenization treatment (solution treatment) as necessary.

Next, the raw material alloy obtained in the above steps is pulverized. The atmosphere in each step from the pulverization step to the sintering step preferably has a low oxygen concentration from the viewpoint of obtaining high magnetic properties. The low oxygen concentration atmosphere is, for example, an atmosphere with an oxygen concentration of 200 ppm or less. By controlling the oxygen concentration in each step, the amount of oxygen contained in the magnet base material 20 and the finally obtained permanent magnet 2 can be controlled.

The pulverization process is carried out in two steps of coarse pulverization and fine pulverization. However, the raw material alloy may be pulverized in one stage of only the fine pulverization step.

In the coarse pulverization step, coarse pulverization is performed until the particle size reaches about several hundred μm to several mm to obtain a coarsely pulverized powder. The method of coarse pulverization is not particularly limited, and for example, a method of performing hydrogen absorption pulverization, a method of using a coarse pulverizer, or the like can be adopted. When hydrogen absorption pulverization is performed, the amount of nitrogen contained in the magnet base material 20 and the finally obtained permanent magnet 2 can be controlled by controlling the nitrogen gas concentration in the atmosphere during dehydrogenation.

Next, the obtained coarsely pulverized powder is finely pulverized to an average particle size of about several μm to obtain a finely pulverized powder (raw material alloy powder). The average particle size of the finely pulverized powder is not particularly limited. By controlling the nitrogen gas concentration in the atmosphere in the pulverization step, the nitrogen content in the magnet base material 20 and the finally obtained permanent magnet 2 can be controlled.

The fine pulverization method is not particularly limited, and various fine pulverizers can be used. Further, it is preferable to add a pulverizing aid during the fine pulverization, and examples of the pulverizing aid include lauric acid amide and oleic acid amide. By using a grinding aid, a highly oriented finely ground powder can be obtained during molding. The amount of carbon contained in the magnet base material 20 and the finally obtained permanent magnet 2 can be controlled by changing the amount of the grinding aid added.

In the above steps (from the preparation step of the raw material alloy to the pulverization step), the raw material alloy powder was obtained by the one-alloy method, but the raw material alloy powder is produced by mixing two alloys, the first alloy and the second alloy. A two-alloy method may be employed.

Next, the obtained raw material alloy powder is formed into a predetermined shape. The molding method is not particularly limited, and may be dry molding or wet molding. In this embodiment, the raw material alloy powder is filled in a mold and pressed in a magnetic field (dry compaction).

The pressure during molding can be, for example, 20 MPa to 300 MPa, and the applied magnetic field can be 950 kA/m to 1600 kA/m. The magnetic field to be applied is not limited to a static magnetic field, and may be a pulsed magnetic field, or both a static magnetic field and a pulsed magnetic field may be used. When wet molding is employed, the raw material alloy powder is dispersed in a solvent such as oil to form a slurry, and the slurry is press-molded in the same manner as described above.

Next, the compact is sintered in vacuum or in an inert gas to obtain a sintered body. The sintering conditions may be appropriately determined according to various conditions such as the composition, pulverization method, and grain size of the raw material alloy powder. For example, the compact can be sintered by holding the compact at a temperature of 1000° C. to 1200° C. for 1 hour to 10 hours in vacuum or inert gas.

After the sintering step, the sintered body may be subjected to decarbonization treatment, if necessary. The decarbonization method is not particularly limited, and a known method may be adopted. For example, the carbon content in the sintered body can be reduced by attaching a predetermined metal S to the sintered body and heat-treating the sintered body. In the above, the predetermined metal S is a metal whose standard Gibbs energy of formation for forming metal carbide from the metal is lower than that of the rare earth element (especially Nd) in the sintered body. By attaching the metal S to the sintered body and heat-treating the sintered body, the carbon in the sintered body reacts with the metal S to form a carbide. The attached metal S hardly penetrates into the sintered body and stays on the surface of the sintered body. By performing the decarbonization treatment as described above, the amount of carbon contained in the magnet base material 20 and the finally obtained permanent magnet 2 can be reduced.

Further, the sintered body may be subjected to shape processing such as cutting and grinding, chamfering processing such as barrel polishing, and the like, if necessary. These processes are performed before the diffusion process described later.

By the above method, the magnet base material 20 shown in FIGS. 1 and 3A is obtained.

(Grain boundary diffusion process)
Next, grain boundary diffusion processing (first diffusion step and second diffusion step) will be described. In this embodiment, as described above, the first diffusion step of mainly diffusing the light rare earth element into the magnet base material 20 and the second diffusion step of mainly diffusing the heavy rare earth element into the magnet base material 20 are carried out. (See Figure 2).

Preparation of Diffusion Material First, the first diffusion material 11 used in the first diffusion process and the second diffusion material 12 used in the second diffusion process are prepared.

The first diffusing material 11 contains at least one light rare earth element (RL), and the added RL is preferably one or more elements selected from the group consisting of Nd and Pr. . The first diffusing material 11 can be a pure metal, an alloy, or a compound containing RL such as a hydride, and is particularly preferably an RL-M alloy containing RL and a predetermined M element.

In the above, the M element is an element whose eutectic temperature between M and RL is 800° C. or less, and specifically Al, Mg, Fe, Mn, Co, Ni, Cu, Zn, Ga, Ge, Ru , Rh, Pd, Ag, Sn, Sb, Pt, Au, Hg, Bi, Si, and Cl. Preferably, the M element is an element in which the eutectic temperature between M and RL is 700° C. or less. , Hg, Si, and Cl. More preferably, the M element is an element in which the eutectic temperature between M and RL is 600° C. or lower, specifically Mg, Co, Ni, Cu, and Cl. More preferably, the M element is Cu or Co.

Further, if the sum of the contents of the rare earth element R and the M element contained in the first diffusion material 11 (that is, R+M or RH+RL+M) is 100% by mass, the content of the M element in the first diffusion material 11 (RL-M alloy) is Although the total content depends on the type of M element to be selected, it is preferably 5% by mass to 20% by mass, for example. In particular, when Cu is added as the M element, the content of Cu in the first diffusion material 11 (RL-M alloy) is preferably 10% by mass to 15% by mass. The above content rate is the ratio of the M element to 100% by mass of the first diffusion material. By including the M element in the first diffusion material 11 , the melting point of the first diffusion material 11 is lowered, and RL is easily diffused into the magnet base material 20 .

The first diffusing material 11 may contain a heavy rare earth element (RH). The ratio is preferably 10% by mass or less. However, it is more preferable that the first diffusion material 11 does not substantially contain RH. “Substantially free of RH” more specifically means that the RH content is less than 0.5% by mass.

On the other hand, the second diffusing material 12 contains at least one heavy rare earth element RH, and the added RH is preferably one or more elements selected from the group consisting of Tb and Dy. . The second diffusing material 12 can be a pure metal, an alloy, or a compound containing RH such as _TbH2 , and is particularly preferably an RH-M alloy containing RH and M elements. The M element in the second diffusing material 12 is the same as the M element in the first diffusing material 11 , and the addition amount of the M element can be the same as in the first diffusing material 11 . The type of the M element selected for the first diffusing material 11 and the second diffusing material 12 may be different or may be the same.

In addition to the RH and M elements, the second diffusing material 12 may contain RL. In this case, the sum of the contents of the R and M elements contained in the second diffusing material (that is, R+M or It is preferable that the content of RL is 22.5% by mass or less with respect to 100% by mass of RH+RL+M). Also, in the second diffusion material 12, it is preferable to adjust the amounts of the RL and M elements added so that the RH content is 60% by mass or more.

First Diffusion Step In the first diffusion step, the above-described first diffusion material 11 is adhered to at least a part of the surface of the magnet base material 20, and then the magnet base material 20 is heat-treated under predetermined conditions to obtain the first diffusion material. The RL and M elements in the diffusing material 11 are diffused inside the magnet base material 20 .

It is preferable that the surface of the magnet base material 20 to which the first diffusing material 11 is attached is at least part of the main surface 20a serving as the magnetic pole surface. In this case, the first diffusion material 11 may be attached to only one main surface 20a of the pair of main surfaces 20a, or the first diffusion material 11 may be attached to both of the main surfaces 20a. When the thickness of the magnet base material 20 in the Z-axis direction (the distance between the magnetic pole faces) is as thin as 2 mm or less, it is preferable to attach the first diffusing material 11 only to one main surface 20a. Also, the first diffusing material 11 may be adhered to at least a portion of the side surface 20b that serves as the non-magnetic pole surface. The number of surfaces on which the first diffusing material 11 is attached and the area of attachment thereof may be appropriately determined according to the dimensions of the magnet base material 20 and the application of the intended RTB permanent magnet 2 . In this embodiment, as an example, the first diffusing material 11 is attached to the entire surface of the main surface 20a above the Z axis.

Also, the method of adhering the first diffusing material 11 to the surface of the magnet base material 20 is not particularly limited. , sheet construction method, etc. can be used.

When the sheet construction method is employed, powdery first diffusion material 11 and a binder are mixed to produce a sheet 11a of the first diffusion material as shown in FIG. to adhere to. When the sheet 11a is adhered to the magnet base material 20, an organic solvent such as alcohol, aldehyde, or ketone may be applied to the surface of the sheet 11a or the surface of the magnet base material 20. FIG.

Moreover, when adopting the coating method, a slurry is prepared by dispersing the powdery first diffusion material 11 in an organic solvent such as alcohol, aldehyde, or ketone. Then, the slurry is applied to the surface of the magnet base material 20 using a spray, a brush, a jet dispenser, a nozzle, or the like. A binder may be added to the slurry so that the first diffusing material 11 can easily adhere to the surface of the magnet base material 20 . Alternatively, a paste having a higher viscosity than slurry may be prepared using the first diffusing material 11 and the paste may be applied to the surface of the magnet base material 20 . In various printing methods, the above paste may be printed on the surface of the magnet base material 20 .

As described above, the first diffusing material 11 can be attached to the magnet base material 20 by a plurality of methods. It is preferable that it is controlled so that it is satisfied. That is, the total amount of RL to be attached is 0.1 to 2.0 parts by mass (more preferably 0.4 to 1.5 parts by mass) with respect to 100 parts by mass of the magnet base material. Moreover, it is preferable to control the adhesion amount of the first diffusion material 11 .

As for the conditions of the heat treatment in the first diffusion step, the heat treatment atmosphere is preferably in a vacuum or in an inert gas, the holding temperature is preferably more than 700° C. and 1000° C. or less, and the temperature holding time is 1 hour or more and 24 hours or less. is preferred. Moreover, it is preferable to rapidly cool the magnet base material 20 after a predetermined holding time has passed. By performing the heat treatment under the above conditions, the RL contained in the first diffusion material 11 (the RL and the M element when the M element is contained) diffuses into the grain boundaries 6 of the magnet base material 20 .

By diffusing RL inside the magnet base material 20 in the first diffusion step, the grain boundary 6 (particularly, the two-particle grain boundary 6a) spreads, and in the second diffusion step described later, RH diffuses around the center of the magnet base material 20. It is thought that it will be easier to spread to When the magnet base material 20 contains only Nd as R and the first diffusing material 11 contains RL other than Nd, such as Pr, the first diffusion step causes the main phase particles 4 to A shell containing RL other than Nd may be formed at the periphery. It is considered that the shell is formed by substituting part of R(Nd) in the R ₂ T ₁₄ B crystal with RL other than Nd.

After the first diffusion step, residues such as an oxide film may remain on the surface of the magnet base material 20 in some cases. Therefore, it is preferable to perform a processing step for removing the residue after the first diffusion step. The method of removing the residue is not particularly limited. For example, chemical removal such as etching, physical cutting, shape processing such as grinding, or chamfering such as barrel polishing may be performed.

Second Diffusion Step Next, the second diffusion step is carried out using the second diffusion material 12 described above. In the second diffusion step, after the second diffusing material 12 is adhered to at least a part of the surface of the magnet base material 20 , the magnet base material 20 is heat-treated under predetermined conditions so that the RH in the second diffusing material 12 is and M elements are diffused inside the magnet base material 20 .

The second diffusing material 12 is preferably adhered to the surfaces (main surface 20a and side surfaces 20b) of the magnet base material 20 to which the first diffusing material 11 is adhered in the first diffusion step. For example, as shown in FIG. 2, when the first diffusing material 11 is attached to the main surface 20a (magnetic pole surface) above the Z axis, the second diffusing material 12 is similar to the first diffusing material 11 in the Z axis direction. It is preferably attached to the upper major surface 20a. The adhesion area of the second diffusing material 12 may be larger or smaller than the adhesion area of the first diffusing material 11, but it is preferable that they are approximately the same. When the attachment area of the second diffusing material 12 is reduced, it is preferable to attach the second diffusing material 12 to a portion of the obtained permanent magnet where the coercive force HcJ is particularly desired to be improved.

The method of attaching the second diffusing material 12 is not particularly limited. Similar to the first diffusing step, vapor deposition method, sputtering method, electrodeposition method, coating method, printing method (screen printing, squeegee printing, etc.), A sheet construction method or the like can be used. FIG. 2 shows, as an example, the use of a sheet 12a of the second diffusing material, which is obtained by mixing the powdery second diffusing material 12 and a binder to form a sheet.

Moreover, it is preferable that the adhesion amount of the second diffusing material is controlled so as to satisfy a predetermined condition. That is, the total amount of RH to be attached is 0.3 parts by mass to 2.0 parts by mass (more preferably 0.4 parts by mass to 1.0 parts by mass) with respect to 100 parts by mass of the magnet base material. In addition, it is preferable to control the adhesion amount of the second diffusion material 12 .

As for the conditions of the heat treatment in the second diffusion step, the heat treatment atmosphere is preferably in a vacuum or in an inert gas, the holding temperature is preferably more than 700° C. and 1000° C. or less, and the temperature holding time is 1 hour or more and 24 hours or less. is preferred. Moreover, it is preferable to rapidly cool the magnet base material 20 after a predetermined holding time has passed. By performing the heat treatment under the above conditions, RH contained in the second diffusion material 12 (RH and the M element when the M element is contained) diffuses into the grain boundaries 6 of the magnet base material 20 . Note that the second diffusion step may include an aging step. The aging step is preferably carried out by holding the magnet substrate 20 at a temperature of 450° C. to 700° C. for 0.2 to 3 hours in vacuum or in an inert gas after the rapid cooling. After the passage of time, quenching is preferred.

The RH diffused to the grain boundary 6 in the second diffusion step reacts with part of the R ₂ T ₁₄ B crystals at the outer edge of the main phase grain 4 and is concentrated. That is, after the second diffusion step, as shown in FIG. 3B, a shell portion 42 having a high RH content is formed in the main phase particle 4 in the region where RH diffuses, and the main phase particle 4 becomes a core-shell Particles 4a are obtained. The core-shell particles 4a will be described in detail in the description of the RTB system permanent magnet 2 below.

It should be noted that, after the second diffusion step as well, it is preferable to carry out a process for removing residues, as in the case after the first diffusion step. The method of removing the residue is not particularly limited. For example, chemical removal such as etching, physical cutting, shape processing such as grinding, or chamfering such as barrel polishing may be performed.

By the above method, an RTB system permanent magnet 2 (FIG. 4A) having both high residual magnetic flux density and high coercive force is obtained. The characteristics of the RTB permanent magnet 2 obtained by the manufacturing method of this embodiment will be described below.

(RTB system permanent magnet 2)
In the RTB system permanent magnet 2 (hereinafter referred to as the permanent magnet 2) of this embodiment shown in FIG. 4A, a pair of main surfaces 2a are magnetic pole surfaces. The main surface 2a on the axis is the surface to which the first diffusion material 11 and the second diffusion material 12 are attached. In FIG. 4A, the permanent magnet 2 has a rectangular parallelepiped shape in accordance with the shape of the magnet base material 20 in FIG. However, the shape and dimensions of the permanent magnet 2 are not particularly limited, and may be, for example, a polygonal shape, a cylindrical shape, a hollow cylindrical shape, or an arc segment shape whose main surface is curved in an arc shape.

The permanent magnet 2 has a composition slightly different from the composition of the magnet base material 20 used at the time of manufacture due to grain boundary diffusion of RL and RH in this order during the manufacturing process.

Specifically, in the permanent magnet 2, R includes at least one light rare earth element (RL) essentially including Nd and at least one heavy rare earth element (RH). RL other than Nd preferably contains Pr, and RH preferably contains Tb and/or Dy.

The total content of R with respect to 100% by mass of the permanent magnet can be 25% by mass to 35% by mass, preferably 28.4% by mass or more and 32.0% by mass or less. Further, the total content of RL is preferably 26.0% by mass or more and 31.5% by mass or less, and the total content of RH is preferably 0.3% by mass or more with respect to 100% by mass of the permanent magnet. It is preferably 3.0% by mass or less. In addition, the content of Nd with respect to 100% by mass of the permanent magnet is preferably 22.4% by mass or more and 31.5% by mass or less.

As described above, in the permanent magnet 2 , the R content increases more than the R content in the magnet base material 20 depending on the amount of RL and RH diffused by the diffusing materials (11, 12). On the other hand, the content of B in the permanent magnet 2 can be made approximately the same as the content of B in the magnet base material 20 . That is, the content of B with respect to 100% by mass of the permanent magnet can be 0.5% by mass to 1.5% by mass, preferably 0.92% by mass to 1.03% by mass. When the content of B satisfies the above composition range, the magnetic properties (Br, HcJ, squareness ratio Hk/HcJ, etc.) of the permanent magnet 2 tend to be further improved.

Further, the permanent magnet 2 preferably contains the element M added to the first diffusing material 11 and/or the second diffusing material 12 . The content C _M of the element M caused by the diffusing materials (11, 12) is preferably 0.5% by mass or less, and is preferably 0.05% by mass or more and 0.2% by mass with respect to 100% by mass of the permanent magnet. % or less. For example, when an element M _NO (Ag, Au, etc.) that is not substantially contained in the magnet base material 20 is selected as the M element added to the diffusing material, the above content C _M It becomes the content of _MNO . On the other hand, when the element MIN originally contained in the magnet base material 20 is selected as the M _element added to the diffusing material, the content of the element _MIN in the permanent magnet 2 is the same as the content in the magnet base material 20. , the range obtained by _adding the above content rate CM.

For example, when Fe, Co, or Ni is added to the first diffusing material 11 and/or the second diffusing material 12, the T content in the permanent magnet 2 slightly increases from that in the magnet base material 20 during the manufacturing process. (additional content C _M above). Note that the content of T in the permanent magnet 2 is expressed as the remainder. The T of the permanent magnet 2 may be composed solely of Fe, or part of Fe may be replaced with Co. In this case, the Co content is not particularly limited, and can be, for example, 4% by mass or less, preferably 1% by mass or less. Containing Co improves the corrosion resistance of the permanent magnet 2 .

The permanent magnet 2 preferably contains one or more m elements selected from the group consisting of Cu, Ga, Al, and Zr, and more preferably contains Cu as the m element. preferable. This m element is added to the permanent magnet 2 due to the magnet base material 20 and/or the diffusion materials (11, 12). The total content of m elements with respect to 100% by mass of the permanent magnet is preferably 0.05% by mass or more and 1.5% by mass or less, more preferably 0.5% by mass or more and 1.0% by mass or less. .

More specifically, the content of Cu with respect to 100% by mass of the permanent magnet can be 0.05% by mass or more and 0.70% by mass or less, preferably 0.20% by mass or more and 0.70% by mass. . By containing Cu in the above ratio, the magnetic properties and corrosion resistance of the permanent magnet 2 are further improved. Moreover, when Ga, Al, and Zr are included as the m element, the content of these elements is not particularly limited. For example, the Ga content can be 0.08% by mass or more and 0.50% by mass or less, preferably 0.08% by mass or more and 0.3% by mass or less. Both the Al content and the Zr content can be 0.10% by mass or more and 0.50% by mass or less, and preferably 0.10% by mass or more and 0.30% by mass or less. By including Ga, Al, Zr, etc. in the above-mentioned predetermined amounts, it is possible to further improve magnetic properties (Br, HcJ, Hk/HcJ, etc.), reduce variations in properties, and improve manufacturing stability.

The permanent magnet 2 may also contain carbon (C), nitrogen (N), and oxygen (O). The carbon content in the permanent magnet 2 is preferably 1100 mass ppm or less, more preferably 900 mass ppm or less. The nitrogen content in the permanent magnet 2 is preferably 1000 mass ppm or less, more preferably 600 mass ppm or less. The coercive force HcJ tends to improve as the carbon content rate and the nitrogen content rate decrease. The oxygen content in the permanent magnet 2 is preferably 1200 ppm or less, more preferably 800 ppm or less. Corrosion resistance tends to improve as the oxygen content decreases.

Furthermore, the permanent magnet 2 may contain unavoidable impurities such as Mn, Ca, Cl, S, and F in addition to the elements described above. % to 1.0% by mass.

The composition of the permanent magnet 2 is determined by XRF, ICP, inert gas fusion - non-dispersive infrared absorption method, combustion in oxygen current - infrared absorption method, inert gas fusion - in the same manner as the composition analysis of the magnet base material 20. It can be measured by a thermal conductivity method or the like.

Inside the permanent magnet 2 in this embodiment, a concentration distribution of a predetermined element occurs. Specifically, the total RL content decreases continuously from the main surface 2a (magnetic pole surface) in the depth direction (that is, from the surface of the permanent magnet 2 toward the inside). Such a concentration distribution of RL is caused by grain boundary diffusion of RL in the first diffusion step. In the permanent magnet 2, the total RH content decreases continuously from the main surface 2a (magnetic pole surface) in the depth direction. This concentration distribution of RH is caused by grain boundary diffusion of RH in the second diffusion step.

Furthermore, in the permanent magnet 2, the content of the M element (preferably one or more selected from Cu, Al, Fe, and Co) decreases continuously in the depth direction from the main surface 2a (pole surface). preferably. Such concentration distribution of the M element is generated by grain boundary diffusion of the M element in the diffusion materials (11, 12) in the first diffusion step and/or the second diffusion step. Note that when an iron group element (Fe, Co, or Ni) is added as the M element to the diffusing materials (11, 12), the concentration distribution of the M element described above becomes the T concentration distribution. Therefore, when an iron group element is selected as the M element of the diffusing material, it is preferable that the content of T continuously decreases in the depth direction from the main surface 2a (pole surface).

Note that the concentration distribution of each element (RL, RH, M element) described above can be confirmed using a plurality of samples β shown in FIG. 4B. Specifically, a sample β having a predetermined width Tβ (the width in the Z-axis direction) is continuously sampled from the main surface 2a along the depth direction (inward direction of the permanent magnet 2), and a plurality of sample samples are sampled. β are each subjected to component analysis using ICP. At this time, the predetermined width Tβ is preferably 1 mm or less, or preferably Tβ<(1/10)×T0.

In the permanent magnet 2 of the present embodiment, as a result of the above analysis, the total content of RL, the total content of RH, and the content of M continuously and gradually decrease as the sampling location of the sample β becomes deeper. A trend can be confirmed. In particular, the difference (β1−β _center ) in the content of the predetermined element between the sample β1 on the outermost surface and the sample β _center in the central portion (sample β collected at a depth of 1/2T0 from the main surface 2a) is measured. In this case, the difference in the total RL content is preferably about 0.1% by mass to 0.5% by mass, and the difference in the total RH content is preferably 0.1% by mass to 0.5% by mass. It is preferable that the difference in the content of the M element is about 0.1% by mass to 0.3% by mass.

The concentration distribution of each element (RL, RH, M element) can be measured by line analysis or mapping analysis by EDX or EPMA, or laser ablation-ICP mass It can also be confirmed by performing an analysis (LA-ICP-MS).

FIG. 3B is a schematic diagram showing an enlarged cross section of the permanent magnet 2 in this embodiment. As described above, in the permanent magnet 2, the main phase particles 4 are core-shell particles 4a in the RH diffused region. This core-shell particle 4 a has a core portion 41 made of R ₂ T ₁₄ B crystals and a shell portion 42 covering the core portion 41 and having a higher heavy rare earth element content than the core portion 41 . The average particle diameter of the core-shell particles 4a is not particularly limited.

Note that the shell portion 42 does not need to cover the entire circumference of the core portion 41 , and may cover at least a portion of the core portion 41 . Although the coverage of core portion 41 by shell portion 42 is not particularly limited, for example, 50% or more of the outer peripheral edge of core portion 41 is preferably covered by shell portion 42 . Moreover, in the cross section as shown in FIG. 3B, not all main phase particles 4 need to be core-shell particles 4a, and main phase particles 4 having no core-shell structure may be present.

As described above, the formation of the shell portion 42 in which the RH is concentrated around the outer periphery of the main phase grain 4 suppresses the generation of nuclei of magnetization reversal near the grain boundary, thereby improving the coercive force HcJ. can.

In addition, in the permanent magnet 2 of the present embodiment, compared to the conventional permanent magnet in which RH is diffused by only one step of grain boundary diffusion treatment, the vicinity of the surface where RH is diffused (in this embodiment, the main surface 2a The shell thickness of the core-shell particles 4a in the vicinity) can be reduced. Actually, FIG. 6 is a cross-sectional photograph of the permanent magnet 2 of the present embodiment subjected to two-step grain boundary diffusion treatment, and FIG. 7 is a photograph of a conventional permanent magnet subjected to only one-step grain boundary diffusion treatment. It is a cross-sectional photograph. 6 and 7 are cross sections perpendicular to the surface (principal surface 2a) to which the diffusion material is adhered, and are cross sections obtained by observing a range from the surface to a predetermined depth. In FIGS. 6 and 7, the brightest contrast is the grain boundary phase, the darkest contrast is the core portion 41 (main phase grain 4), and the gray contrast surrounding the core portion 41 is It is the shell part 42 .

In the conventional permanent magnet shown in FIG. 7, it can be clearly recognized that there is a gray shell part around the core part, and a thickness of submicron order to micron order in the vicinity of the surface (range up to 100 μm in depth). It can be confirmed that a shell portion is formed. On the other hand, in the cross section of the permanent magnet 2 of this embodiment shown in FIG. 6, it can be seen that the thickness of the shell portion 42 near the surface is clearly thinner than that of the conventional permanent magnet shown in FIG.

More specifically, in the permanent magnet 2 of the present embodiment, the maximum thickness t1 of the shell portion 42 is 0.5 μm or less on average in the section A at a depth of 100 μm from the surface (principal surface 2a), and 0.5 μm. It is preferably 2 μm or less, more preferably 0.1 μm or less. By controlling the maximum thickness t1 of the shell portion 42 in the vicinity of the surface of the permanent magnet 2 within the above range, a higher residual magnetic flux density Br and a higher coercive force HcJ can be obtained than the conventional permanent magnet shown in FIG. is obtained. The reason why the magnetic properties are improved in this way is not necessarily clear, but it is thought that the RH concentration in the shell portion 42 is related. Specifically, it is considered that the RH concentration in the shell portion 42 becomes higher than that in the conventional permanent magnet (FIG. 7) by reducing the thickness of the shell portion 42 . As a result, in the permanent magnet 2 of this embodiment, it is considered that HcJ can be improved more efficiently without lowering Br.

In addition, in the permanent magnet 2 of the present embodiment, the thickness of the shell portion 42 is reduced in the vicinity of the surface as described above, and RH diffuses deeper into the permanent magnet 2 . Specifically, in the permanent magnet 2, even when the diffusing materials (11, 12) are attached only to the main surface 2a on one side, the core-shell particles 4a extend from the main surface 2a to a depth of 3.5 mm. can be confirmed, and the effect of improving HcJ can be expected up to a depth of 3.5 mm.

The maximum thickness t1 of the shell portion 42 is calculated, for example, based on STEM-EDS analysis. First, at a position 100 μm deep from the main surface 2a to which the diffusion materials (11, 12) are attached, a cross section A (for example, the XY plane indicated by the dashed dotted line in FIG. 4B) is exposed, and from the cross section Observation samples are taken. As a method for sampling, a microsampling method using FIB processing or the like may be adopted.

Then, the main phase particles 4 (core-shell particles 4a) contained in the collected observation sample (observation cross section) are analyzed by STEM-EDS. In this embodiment, the core portion 41 and the shell portion 42 are distinguished based on the concentration difference Dc of the heavy rare earth element and the concentration E of the heavy rare earth element. Specifically, when performing the cross-sectional analysis, a virtual rectangle VR (see FIG. 5) that contains the main phase particles 4 to be measured and has the smallest area with respect to the main phase particles 4 is prepared. Let the intersection be the particle center 41c. Then, after obtaining the concentration distribution of RH and the concentration distribution of RL in the main phase particles 4 by _EDS , the difference ( _{Ch n} −Ch _center ) is the RH concentration difference Dc (unit: wt %). Further, the molar ratio of RH to RL at a predetermined location is defined as _MH/L ⁿ , the molar ratio of RH to RL at the particle center 41c is defined as _MH/L ^center , and the ratio of _MH/L ⁿ to _MH/L ^center is the RH concentration E (unit: none).

In the present embodiment, the shell portion 42 has the concentration difference Dc of 0.7 wt % or more and the concentration E of 1.25 or more. That is, in the cross-sectional analysis, the region that satisfies the two requirements is identified as the shell portion 42 , and the region other than the shell portion 42 of the main phase particle 4 is identified as the core portion 41 . However, the RH concentration detected at the particle center 41c may be less than 0.2 wt%. In this case, considering the measurement noise, it is assumed that RH is not substantially detected at the particle center 41c (that is, Ch _center ≈ 0), and the RH concentration is 0.7 wt% or more (that is, the concentration difference Dc is 0.7 wt% % or more) can be identified as the shell portion 42 . Note that when the cross-sectional sample is observed with an HAADF image or the like, it is also possible to easily distinguish between the core portion 41 and the shell portion 42 due to the difference in contrast.

After defining the boundary between the core portion 41 and the shell portion 42 by the method described above, as shown in FIG. 5, the thickness of the thickest portion of the shell portion 42 within the unit particle is measured. The measurement is performed for at least 20 core-shell particles 4a, and the average value is taken as the maximum thickness t1 described above. The shell thickness can also be analyzed using a three-dimensional atom probe (3DAP).

Also, the diffusion depth of RH can be measured by analyzing samples β (FIG. 4B) continuously taken along the depth direction from the surface (principal surface 2a) of the permanent magnet 2 . For example, by observing the cross sections of a plurality of samples β with an STEM and confirming the presence or absence of the core-shell particles 4a, it is possible to measure to what depth the RH has diffused. Further, by measuring the magnetic properties of a plurality of collected samples β using various BH tracers, it is possible to determine the depth to which an increase in HcJ is observed.

As for the magnetic properties of the permanent magnet 2, specifically, it is preferable that Br is 1450 mT or more and HcJ is 1800 kA/m or more. Since the permanent magnet 2 satisfies the magnetic properties, it is possible to improve the performance and efficiency of the motor having the permanent magnet 2 .

(Application field of RTB system permanent magnet 2)
The RTB system permanent magnet 2 of this embodiment can be used as a component of motors, generators, compressors, actuators, magnetic sensors, speakers, etc., and is particularly suitable as a component of motors.

As a motor using the permanent magnet 2, for example, there is an IPM motor 50 as shown in FIG. The IPM motor 50 has a rotor 51 and a stator core 52 , and the permanent magnets 2 of this embodiment are embedded in the rotor 51 . The permanent magnets 2 in the rotor 51 face the coils 54 present in the stator through the gaps 53 . The permanent magnet 2 of this embodiment is not limited to the IPM motor shown in FIG. 8, and can be applied to various motors such as an SPM motor.

In addition, the motor including the permanent magnet 2 of the present embodiment can be mounted on various electronic equipment, industrial equipment, etc., and in particular, as an automobile motor 50 (EV, HV, PHV, etc.) as shown in FIG. Use is preferred. Although FIG. 9 shows a general EV vehicle 101 and HV 102 in a simple schematic diagram, the application of the motor including the permanent magnet 2 is not limited to the mode shown in FIG. In FIG. 9, reference numeral 60 is an inverter, reference numeral 70 is a battery, reference numeral 80 is an engine, and reference numeral 90 is a generator.

(Summary of embodiment)
In the method of manufacturing the RTB permanent magnet 2 according to the present embodiment, after the first diffusion step is performed with the first diffusion material 11 containing the light rare earth element (RL), the first diffusion step containing the heavy rare earth element (RH) is performed. 2. Perform a second diffusion step with the diffusion material 12 . That is, two-step grain boundary diffusion is performed in which RH is diffused after RL is diffused.

In the RTB permanent magnet 2 obtained by this method, the maximum thickness t1 of the shell portion 42 at a depth of 100 μm from the surface of the magnet is thin, t1≦0.5 μm, preferably t1≦0.2. , more preferably t1≦0.1. By reducing the thickness of the shell portion 42 in the vicinity of the surface in this way, it is considered that the RH concentration in the shell portion 42 can be further increased and RH will preferably diffuse into the magnet. As a result, in the RTB system permanent magnet 2, both Br and HcJ are improved compared to the conventional ones. In other words, in the two-step grain boundary diffusion treatment of the present embodiment, a permanent magnet having both a higher residual magnetic flux density Br and a higher coercive force HcJ is obtained as compared with the case where the conventional one-step grain boundary diffusion treatment is performed. A magnet 2 is obtained.

Although the reason why the above effect can be obtained by the two-step grain boundary diffusion treatment is not necessarily clear, for example, the following reasons can be considered.

First, it is considered that suppression of decomposition of R ₂ T ₁₄ B crystals (main phase) by RH is related. In the grain boundary diffusion treatment, when RH permeates along the grain boundary and comes into contact with the R ₂ T ₁₄ B crystal in a heated state, the outer edge of the R ₂ T ₁₄ B crystal (particularly the Nd ₂ Fe ₁₄ B crystal) becomes RH. It is thought to react and decompose into crystal phases and liquid phases different from the main phase (for example, RFe ₂ phase, RFe ₄ B ₄ phase, etc.). It is believed that the different crystal phases and liquid phases generated by this decomposition are recrystallized to form a shell portion in which RH is concentrated.

Conventionally, when RH is grain boundary diffused in a one-step diffusion process, high-concentration RH comes into contact with the R ₂ T _{14 B} crystal near the surface of the magnet. It is believed that the decomposition reaction of T ₁₄ B crystals actively occurs. As a result, the conventional grain boundary diffusion process forms a thick shell near the surface of the magnet. Although the shell portion in which RH is concentrated has the effect of improving HcJ, the thickness of the shell necessary for improving HcJ is only a few nanometers, and a shell with an excessive thickness warps and causes a decrease in Br. it is conceivable that. In addition, in the conventional step process, a large amount of the deposited RH is consumed near the surface of the magnet, making it difficult to sufficiently diffuse into the interior of the magnet, which is thought to weaken the effect of improving HcJ.

On the other hand, in the two-stage grain boundary diffusion treatment in this embodiment, RL is diffused before RH is diffused. Between the RL and the R ₂ T ₁₄ B crystal (specifically, between the Nd ₂ Fe ₁₄ B crystal and Nd or Pr), no metal compound phase other than R ₂ T ₁₄ B is generated. It is thought that the decomposition reaction of the main phase that occurs between RH and R ₂ T ₁₄ B crystals does not occur in the first diffusion step of . Therefore, after the first diffusion step, the RL is concentrated at the grain boundary 6, and the RL concentration is considered to be higher than before the first diffusion step. By diffusing RH in this state (second diffusion step), it is considered that the ratio of RH to all rare earth elements at grain boundaries 6 can be relatively reduced.

In other words, in the two-stage grain boundary diffusion treatment of the present embodiment, RH comes into contact with the R ₂ T ₁₄ B crystal at a lower concentration than in the conventional one-stage diffusion, and the decomposition reaction of the main phase is suppressed. It is thought that As a result, in the present embodiment, the thickness of the shell portion 42 can be made thinner than in the conventional one-stage diffusion, and it is thought that the RH concentration in the shell portion 42 can be increased by the amount of the reduced thickness. can be maintained. In addition, in the present embodiment, it is believed that the suppression of the decomposition reaction of the main phase suppresses the consumption of RH in the vicinity of the surface of the magnet, and facilitates the diffusion of RH into the interior of the magnet. As a result, the effect of improving HcJ by diffusion of RH is enhanced, and it is considered that both high HcJ and high Br can be achieved.

In addition, the reason why RH is likely to diffuse into the interior is considered to be that the two-particle grain boundary 6a is expanded due to the diffusion of RL in the first diffusion step. It is believed that the expansion of the grain boundaries 6 by the RL makes it easier for the RH to permeate into the interior of the magnet in the second diffusion step, resulting in a higher HcJ than the conventional method. Furthermore, in the manufacturing method of the present embodiment, the grain growth of the main phase grains 4 in the second diffusion step is thought to be suppressed by diffusing RL before diffusing RH, and the effect of suppressing grain growth is It is believed that this contributed to the improvement of the magnetic properties.

In addition, the above-described principle regarding the modification of the grain boundary 6 (suppression and expansion of the decomposition reaction) is merely an inference, and the effects of the present invention are not limited to the above. In addition, in the manufacturing method (two-stage grain boundary diffusion treatment) of the present embodiment, the amount of RH required to obtain magnetic properties (especially HcJ) comparable to those of conventional permanent magnets can be reduced. . This is because, as described above, the two-step grain boundary diffusion treatment of this embodiment can reduce the thickness of the shell near the surface and diffuse RH deeper into the magnet.

In addition, when the magnet base material 20 used in manufacturing has a predetermined composition, the effect of improving Br and HcJ described above becomes more remarkable. That is, in the magnet base material 20 (RTB alloy), the total R content is 27.5% by mass or more and 30.8% by mass or less, and the Cu content is 0.05% by mass. % or more and 0.5 mass % or less, and the B content is 0.92 mass % or more and 1.03 mass % or less. In this composition, the total content of R is lower than the composition range of general RTB alloys. Thus, by using the magnet base material 20 with a low R content, the effect of improving Br and HcJ by the two-stage grain boundary diffusion treatment is further enhanced.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

EXAMPLES The present invention will be described in more detail below using examples and comparative examples. However, the present invention is not limited to the following examples.

Experiment 1
In Experiment 1, the composition of the magnet base material 20 was changed and the grain boundary diffusion treatment was performed in two stages to produce RTB permanent magnets according to samples 1 to 21, and the magnetic properties of these samples were evaluated. .

(Samples 1 to 21)
First, Nd, Pr, Tb, DyFe, electrolytic iron, and a low-carbon ferroboron alloy were prepared as raw materials. Also, Al, Ga, Cu, Co, and Zr were prepared in the form of pure metals or alloys with Fe. Then, the raw materials were weighed so that the magnet base material 20 had the composition shown in Table 2, and a raw material alloy was produced by a strip casting method. The thickness of the raw material alloy obtained here was 0.2 mm to 0.6 mm.

Next, hydrogen gas was allowed to flow through the raw material alloy at room temperature for 1 hour to cause hydrogen to be occluded. After that, the atmosphere was changed from hydrogen gas to Ar gas, dehydrogenation treatment was performed at 450° C. for 1 hour, and the raw material alloy was hydrogen pulverized. The pulverized raw material alloy was cooled and then classified using a sieve to obtain a powder having a particle size of 400 μm or less (coarsely pulverized material). In the production of samples other than sample 20, a low-oxygen atmosphere with an oxygen concentration of 200 ppm or less was always used from the hydrogen absorption pulverization to the sintering process described later. On the other hand, for the sample 20, the oxygen concentration in each step was adjusted so that the magnet base material 20 had a predetermined oxygen content.

Next, oleic acid amide was added as a grinding aid to the coarsely ground material and mixed. Then, this coarsely pulverized material was finely pulverized in a nitrogen stream using a collision plate type jet mill to obtain a fine powder (raw material alloy powder) having an average particle size of about 3.9 μm to 4.2 μm. In the pulverization step, the amount of oleic acid amide added was adjusted so that the carbon content in the magnet base material 20 was within the desired range. The above average particle size is the average particle size D50 measured with a laser diffraction type particle size distribution meter.

Next, the raw material alloy powder was compacted in a magnetic field to produce a compact. At this time, the applied magnetic field was a static magnetic field of 1200 kA/m, the pressing force during molding was set to 120 MPa, and the magnetic field application direction and the pressurizing direction were perpendicular to each other. When the densities of the molded bodies obtained in this molding step were measured, the densities of all the molded bodies were within the range of 4.10 Mg/m ³ or more and 4.25 Mg/m ³ or less.

Next, the molded body was sintered to obtain a sintered body made of an RTB alloy. The sintering conditions were held at a temperature of 1040° C. to 1100° C. for 4 hours in a vacuum atmosphere, although the conditions differ slightly depending on the composition. The sintered densities obtained in this sintering process ranged from 7.45 Mg/m ³ to 7.55 Mg/m ³ or less for all samples. After that, the sintered body was vertically processed into a size of 15 mm×10 mm×5 mm (thickness of 5 mm in the direction of easy magnetization) to obtain a magnet base material 20 .

Here, the average composition of the magnet base material 20 in each sample was measured. A sample for analysis was obtained by pulverizing each sample into a size of about 1 mm in average particle size with a stamp mill and randomly extracting the pulverized material. The contents of various metal elements were measured using XRF and ICP. In addition, the oxygen content is measured by an inert gas melting-nondispersive infrared absorption method, the carbon content is measured by combustion in an oxygen stream-infrared absorption method, and the nitrogen content is measured by an inert gas It was measured by the melt-thermal conductivity method. Table 2 shows the measurement results of each sample. The Fe content is the balance, meaning that the content of elements not listed in Table 2 is included in the Fe content, and the total of R, T, B and m is 100% by mass. is.

Subsequently, the magnet base material 20 was subjected to two-step grain boundary diffusion treatment according to the flow shown below. First, a first diffusion material 1A containing Nd(RL) and a second diffusion material 2K containing Tb(RH) having the compositions shown in Table 1 were produced. All of these diffusing materials were alloy powders.

Next, as a pretreatment for grain boundary diffusion, the magnet base material 20 was subjected to an etching treatment. Specifically, a mixed solution of 100% by mass of ethanol and 3% by mass of nitric acid was prepared, and the magnet base material 20 was immersed in the mixed solution for 3 minutes to be etched, and then immersed in ethanol for 1 minute to be washed. The above etching was performed twice for each sample.

Next, the first diffusion material 1A containing Nd: 75 parts by mass, alcohol: 23 parts by mass, and acrylic resin: 2 parts by mass were kneaded to obtain a first paste. The alcohol used at this time was the solvent, and the acrylic resin was the binder. Then, the first paste was applied to both of the pair of magnetic pole faces of the magnet base material 20 . At this time, the amount of the first paste applied was adjusted so that the total amount of Nd adhering to the magnet base material 20 was 1.0 parts by mass with respect to 100 parts by mass of the magnet base material. After applying the first diffusion material 1A, the magnet base material 20 was held at 900° C. for 10 hours in an Ar atmosphere at atmospheric pressure, and then rapidly cooled (first diffusion step). After the first diffusion step, the surface of the magnet base material 20 was polished using No. 1200 abrasive paper until the residue present on the surface was removed.

Next, a second diffusion material 2K containing Tb: 75 parts by mass, alcohol (solvent): 23 parts by mass, and acrylic resin (binder): 2 parts by mass were kneaded to obtain a second paste. Then, the second paste was applied to both of the pair of magnetic pole faces of the magnet base material 20 . At this time, the amount of the second paste applied was adjusted so that the total amount of Tb adhering to the magnet base material 20 was 0.5 parts by mass with respect to 100 parts by mass of the magnet base material. After applying the second diffusion material 2K, the magnet base material 20 was held at 900° C. for 10 hours in an Ar atmosphere at atmospheric pressure, and then rapidly cooled (second diffusion step). After the heat treatment, the magnet base material 20 was heat treated at 600° C. for 1 hour in an Ar atmosphere at atmospheric pressure, and then rapidly cooled (aging step). After the aging process, the surface of the magnet base material 20 was polished using No. 1200 polishing paper until the residue present on the surface was removed.

RTB system permanent magnets 2 according to samples 1 to 21 were obtained through the above steps. The average composition of the RTB permanent magnet 2 was measured in the same manner as the average composition of the magnet base material 20 described above. Table 4 shows the measurement results.

Further, the maximum thickness t1 (the average value of the results of measuring 20 particles) of the shell portion 42 in a cross section at a depth of 100 μm from the magnetic pole surface was measured by the method described in the embodiment. Table 4 shows the measurement results.

Furthermore, the obtained RTB permanent magnet 2 was magnetized by a 4000 kA / m pulse magnetic field, and then using a BH tracer, the residual magnetic flux density Br (mT) and the coercive force HcJ of each sample (kA/m) and squareness ratio Hk/HcJ (%) were measured. In this example, Hk/HcJ was measured as Hk (kA/m), which is the magnitude of the magnetic field when the magnetization J is 90% of Br. A Br of 1450 mT or more was judged to be particularly good, a HcJ of 1800 or more was judged to be particularly good, and a Hk/HcJ of 95% or more was judged to be particularly good. Table 4 shows the measurement results of samples 1 to 21.

Although not shown in Table 4, the presence or absence of concentration distribution of RH (Tb), RL (Nd), and M (Cu) inside each sample was investigated. As a result, it was confirmed that the content of Nd, the content of Tb, and the content of Cu gradually decreased in the depth direction from the pole face in all samples 1 to 21.

(Comparative example)
In Experiment 1, as shown in Tables 3 and 4, RTB permanent magnets according to Comparative Examples 1, 2, 6, 7, 10, 11, 14, 16, 17, 20, 21, and 22 were used. manufactured. Specifically, in Comparative Examples 1, 2, 6, 7, 10, 11, 14, 16, 17, 20, and 21, the above samples 1, 2, 6, 7, 10, 11, 14, 16, A magnet base material having the same composition as those of Nos. 17, 20, and 21 was produced, and only one stage of grain boundary diffusion treatment was applied to the magnet base material using only the diffusing material 2K containing Tb. Comparative Examples 1 to 21 and Samples 1 to 21 correspond to each other in number, and the samples with the same number and the Comparative Example have approximately the same composition of the magnet base material.

In Comparative Example 22, a magnet base material having the same composition A as that of Sample 1 was produced, and then a diffusing material 2K containing Tb(RH) was diffused in the first diffusion step, and Nd(RL) was contained in the second step. Diffusion material 1A was diffused. That is, in Comparative Example 22, the order of diffusion of RH and RL is opposite to that of Sample 1.

In the above comparative examples, experimental conditions other than those described above were common to samples 1 to 21, and the same evaluations as samples 1 to 21 were performed. Tables 3 and 5 show the evaluation results of the comparative examples.

As shown in the results of Tables 4 and 5, when comparing Samples 1 to 21 with corresponding numbers and Comparative Examples 1 to 21, Samples 1 to 21 subjected to two-stage grain boundary diffusion treatment have the corresponding numbers In particular, it can be confirmed that HcJ is improved while maintaining Br. From this result, it was confirmed that a high Br and a high HcJ can be obtained by the two-step grain boundary diffusion treatment.

In addition, in Comparative Examples 1 to 21 in which only one stage of grain boundary diffusion treatment was performed, the maximum thickness t1 of the shell portion near the surface exceeded 0.5 μm, and Sample 1 in which two stages of grain boundary diffusion treatment were performed. It was confirmed that t1 was 0.5 μm or less at ˜21. FIG. 6 is an SEM photograph of the RTB permanent magnet 2 actually obtained in Sample 1, and FIG. 7 is an SEM photograph of the RTB permanent magnet obtained in Comparative Example 1. .

In the SEM photograph of Comparative Example 1 in FIG. 7, it can be confirmed that a thicker shell is formed than in the SEM photograph of FIG. 6, and it can be seen that the shell is particularly thick on the surface side. On the other hand, in the SEM photograph of Sample 1 shown in FIG. From this result, the thickness of the shell portion 42 where RH is concentrated can be reduced by the two-step grain boundary diffusion treatment, and the thickness of the shell portion 42 in the vicinity of the surface can be reduced to a predetermined thickness or less (t1≦0.5 μm). ), both high Br and high HcJ can be realized.

By comparing the evaluation results of samples 1 to 21, when the magnet base material 20 and the RTB system permanent magnet 2 are within a predetermined composition range, 1450 mT≦Br and 1800 kA/m≦HcJ. Satisfied, and tended to improve Br and HcJ.

That is, as the average composition of the magnet base material 20, the total content of R is preferably 27.5% by mass or more and 30.8% by mass or less, and the content of Cu is preferably 0.05% by mass or more. , is preferably 0.5% by mass or less, and the content of B is preferably 0.92% by mass or more and 1.03% by mass or less.

As for the average composition of the RTB permanent magnet 2 after grain boundary diffusion, the total content of R is preferably 28.4% by mass or more and 31.9% by mass or less. The content is preferably 0.2% by mass or more and 0.7% by mass or less, and the content of B is preferably 0.92% by mass or more and 1.03% by mass or less. rice field.

In Comparative Example 22, the maximum thickness of the shell portion in the vicinity of the surface layer exceeded 0.5 μm, resulting in insufficient improvement in magnetic properties. From this result, even if RH and RL are grain boundary diffused in two steps, when RH is grain boundary diffused and then RL is grain boundary diffused, the formation of a thick shell cannot be suppressed, It was found that sufficient magnetic properties could not be obtained.

The reason why the magnetic properties were not sufficiently improved when RH was diffused prior to RL as in Comparative Example 22 is not necessarily clear, but the following reasons are conceivable. First, when RH was diffused before the diffusion of RL, as in the grain boundary diffusion of only one step (Comparative Example 1), a high concentration of RH was in contact with the R ₂ T ₁₄ B crystal, and R ₂ T It is considered that the decomposition reaction of ₁₄ B crystals actively occurred. It is thought that this caused the formation of a thick shell near the surface, leading to the decrease in Br. In addition, it is believed that the diffusion of RL after the diffusion of RH partially destroyed the shell portion containing RH formed in the first diffusion step, weakening the effect of improving HcJ. Furthermore, it is believed that the diffusion of RL increased the thickness of the shell portion containing RH and lowered the RH concentration in the shell portion, weakening the effect of improving HcJ.

As described above, in the two-step diffusion (Comparative Example 22) in which RH diffuses first, it is considered that the thickness of the shell increases and the RH concentration in the shell decreases. As a result, it is considered that Br decreased and HcJ could not be improved sufficiently.

(Experiment 2)
In Experiment 2, a plurality of types of diffusing materials shown in Table 6 were produced, and two-stage grain boundary diffusion treatment was performed using combinations of the diffusing materials shown in Table 7. In Experiment 2, the composition of the magnet base material 20 was the same as the composition A of Sample 1 in Experiment 1, and the RTB permanent magnet 2 was produced under the same conditions as in Experiment 1, except that the composition of the diffusing material was changed. was made. Table 7 shows the evaluation results of Samples 25 to 36 in Experiment 2.

As shown in Table 7, in Samples 25 to 36 of Experiment 2, the maximum thickness t1 of the shell portion 42 was as thin as 0.2 μm or less, and 1450 mT≦Br and 1800 kA/m≦HcJ. From these results, it was found that when the diffusion materials (11, 12) are within the composition range shown in Table 6, both Br and HcJ can be improved. Although not shown in Table 7, in all samples 25 to 36 of Experiment 2, the content of RL, the content of RH, and the content of M element gradually decreased in the depth direction from the pole face. It was confirmed that

Further, comparing Sample 35 and Sample 36, it was found that Tb is more effective than Dy as RH to be diffused. Note that the Dy-diffused sample 36 has a lower HcJ than the other Tb-diffused samples (25 to 35), but it is higher than the case where Dy is diffused by only one step of grain boundary diffusion treatment. It was confirmed that HcJ was obtained.

2 ... RTB system permanent magnet 2a ... main surface (magnetic pole surface)
2b... side surface 4... main phase particle 4a... core-shell particle 41... core part 42... shell part 6... grain boundary 6a... two-particle grain boundary 6b... grain boundary multiple point 20... magnet base material 20a... main surface 20b... side surface 50... IPM motor 51 ... Rotor 52 ... Stator core 53 ... Gap 54 ... Coil 101 ... EV vehicle 102 ... HV vehicle 60 ... Inverter 70 ... Battery 80 ... Engine 90 ... Generator

Claims (14)

preparing a magnet base material containing an RTB alloy;
a first diffusing step of attaching a first diffusing material containing at least one light rare earth element to at least a part of the surface of the magnet base material, and heating the magnet base material to which the first diffusing material is attached;
After the first diffusion step, a second diffusing material containing at least one heavy rare earth element is attached to the surface of at least a part of the magnet base material, and the magnet base material with the second diffusing material attached thereto and a second diffusion step of heating the RTB permanent magnet. 2. The method of manufacturing an RTB permanent magnet according to claim 1, wherein said first diffusing material contains at least one element selected from the group consisting of Nd and Pr as said light rare earth element. 3. The method for producing an RTB permanent magnet according to claim 1, wherein the second diffusing material contains, as the heavy rare earth element, at least one element selected from the group consisting of Tb and Dy. The first diffusion material includes an RL-M alloy containing the light rare earth element and M,
In the RL-M alloy,
RL is the light rare earth element,
4. The method for producing an RTB permanent magnet according to claim 1, wherein M is an element whose eutectic temperature with RL is 800° C. or less. 5. The method for producing an RTB permanent magnet according to claim 1, wherein said first diffusing material does not substantially contain a heavy rare earth element. The RTB alloy contained in the magnet base material contains at least one rare earth element essentially including Nd as R, at least one iron group element essentially including Fe as T, and boron. , Cu, and
In the RTB alloy,
The total content of R is 27.5% by mass or more and 30.8% by mass or less,
Cu content is 0.05% by mass or more and 0.5% by mass or less,
The method for producing an RTB permanent magnet according to any one of claims 1 to 5, wherein the content of B is 0.92% by mass or more and 1.03% by mass or less. RT wherein R is one or more light rare earth elements and one or more heavy rare earth elements consisting essentially of Nd, T is one or more iron group elements consisting essentially of Fe, and B is boron - a B-based permanent magnet,
The RTB permanent magnet contains a plurality of core-shell particles,
Each of the plurality of core-shell particles has a core portion containing R ₂ T ₁₄ B crystals and a shell portion covering the core portion and having a higher content ratio of the heavy rare earth element than the core portion. ,
In a cross section at a depth of 100 μm from the surface of the RTB permanent magnet, the average maximum thickness of the shell portion is 0.5 μm or less,
RT having a concentration distribution in which both the content of the light rare earth element and the content of the heavy rare earth element decrease in the depth direction from the surface of the RTB permanent magnet. - B series permanent magnets. contains an M element whose eutectic temperature with the light rare earth element is 800 ° C. or less,
8. The RTB permanent magnet according to claim 7, having a concentration distribution in which the content of the element M decreases from the surface of the RTB permanent magnet in the depth direction. The RTB system permanent magnet further contains Cu,
The total content of R is 28.4% by mass or more and 32.0% by mass or less,
Cu content is 0.2% by mass or more and 0.7% by mass or less,
9. The RTB system permanent magnet according to claim 7, wherein the B content is 0.92% by mass or more and 1.03% by mass or less. 10. The RTB system permanent magnet according to any one of claims 7 to 9, wherein said heavy rare earth element is Tb and/or Dy. The RTB system permanent magnet according to any one of claims 7 to 10, wherein the light rare earth element further contains Pr. The RTB system permanent magnet according to any one of claims 7 to 11, which has a residual magnetic flux density of 1450 mT or more and a coercive force of 1800 kA/m or more. A motor having the RTB system permanent magnet according to any one of claims 7 to 12. A motor vehicle comprising a motor according to claim 13.

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