RTB-type permanent magnet and method for manufacturing the same

Abstract

It contains at least rare earth elements, Fe, Zr, Cu, B, C, O, and N, with the rare earth element content being 28.50% to 32.00% by mass, the Zr content being 0.01% to 0.50% by mass, the Cu content being 0.04% to 0.50% by mass, the Al content being 0% to 0.60% by mass, the Ga content being 0% to 0.80% by mass, and the Co content being 0% to 3.5% by mass. The composition is 0% by mass or less, with a B content of 0.88% by mass or more and 1.00% by mass or less, a C content of 0.05% by mass or more and 0.12% by mass or less, an O content of 0.11% by mass or more and 0.30% by mass or less, and a N content of 0.015% by mass or more and 0.07% by mass or less, with Fe making up the substantial remainder, and containing heavy rare earth elements as rare earth elements, with a heavy rare earth element content of 0.03% by mass or more and 0.20% by mass or less.

Description

[Technical Field]

[0001] This disclosure relates to RTB-type permanent magnets and methods for manufacturing the same. [Background technology]

[0002] Patent Document 1 discloses an RTB-type permanent magnet whose magnetic properties are improved by having a composition within a specific range. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-8212 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The purpose of this disclosure is to provide an RTB-type permanent magnet with excellent magnetic properties even with a low content of heavy rare earth elements, and a method for manufacturing the same. [Means for solving the problem]

[0005] To achieve the above objectives, the RTB-type permanent magnet relating to this disclosure is It contains at least rare earth elements, Fe, Zr, Cu, B, C, O and N, The content of rare earth elements is between 28.50% by mass and 32.00% by mass. Zr content is 0.01% by mass or more and 0.50% by mass or less. The Cu content is 0.04% by mass or more and 0.50% by mass or less. Al content is 0% by mass or more and 0.60% by mass or less. Ga content is 0% by mass or more and 0.80% by mass or less. Co content is 0% by mass or more and 3.50% by mass or less. The content of B is 0.88% by mass or more and 1.00% by mass or less. The C content is 0.05% by mass or more and 0.12% by mass or less. The O content is 0.11% by mass or more and 0.30% by mass or less, The N content is 0.015% by mass or more and 0.07% by mass or less. Fe is the substantial remainder. It contains heavy rare earth elements as rare earth elements, with a heavy rare earth element content of 0.03% by mass or more and 0.20% by mass or less.

[0006] The residual magnetic flux density Br may be 1400 mT or more, and the coercivity HcJ may be 1900 kA / m or more.

[0007] The RTB-type permanent magnet may include a main phase and a grain boundary triple point surrounded by three or more main phases, the grain boundary triple point may be composed of a rare earth oxide phase and a low melting point grain boundary phase, and the average equivalent circle diameter of the low melting point grain boundary phase may be 0.40 μm or more and 1.00 μm or less.

[0008] The total area ratio of the low-melting-point grain boundary phase may be 1.5% or more and 7.5% or less.

[0009] To achieve the above objectives, the method for manufacturing an RTB-type permanent magnet according to this disclosure is: The process of crushing the alloy to obtain alloy powder, The process of obtaining a molded body by compression molding the aforementioned alloy powder, The process of firing the molded body to obtain a sintered body, The process involves contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, A method for manufacturing an RTB-type permanent magnet, including The amount of oxygen in the alloy powder is controlled before compression molding.

[0010] The alloy may be coarsely ground by hydrogen storage pulverization to obtain a coarse powder, or the coarse powder may be finely ground to obtain the alloy powder.

[0011] The coarse powder may be finely ground using a jet mill.

[0012] The coarse powder may be heat-treated with the oxygen concentration in the atmosphere being 0.5% or more and 23% or less to control the oxygen content of the alloy powder.

[0013] The fine pulverization may be performed with the oxygen concentration in the atmosphere inside the jet mill being 0.01% or more and 0.30% or less to control the oxygen content of the alloy powder.

[0014] The fine pulverization may be performed with the atmosphere inside the jet mill being a mixed gas atmosphere of a noble gas and an oxygen gas to control the oxygen content of the alloy powder.

[0015] The coarse powder may be heat-treated with the oxygen concentration in the atmosphere being 0.5% or more and 23% or less, and the fine pulverization may be performed with the atmosphere inside the jet mill being a mixed gas of a noble gas and an oxygen gas or a noble gas to control the oxygen content of the alloy powder.

[0016] Before and / or after the step of heat-treating the sintered body by bringing it into contact with a diffusion material containing a heavy rare earth element, a step of performing a first aging treatment on the sintered body may be provided.

[0017] Before the step of heat-treating the sintered body by bringing it into contact with a diffusion material containing a heavy rare earth element, a step of performing the first aging treatment may be provided.

[0018] The aging treatment temperature of the first aging treatment may be 850°C or more and 950°C or less, and the aging treatment time of the first aging treatment may be 1.5 hours or more and 10 hours or less.

[0019] Furthermore, after the step of performing the first aging treatment, a step of performing a second aging treatment on the sintered body may be provided.

[0020] After the step of heat-treating the sintered body by bringing it into contact with a diffusion material containing a heavy rare earth element, a step of performing the second aging treatment step may be provided.

Brief Description of the Drawings

[0021] [Figure 1] It is a schematic diagram of the R-T-B-based permanent magnet according to this embodiment. [Figure 2] It is a SEM image of the cross section of the sintered body before grain boundary diffusion of Sample No. 4. [Figure 3] It is a SEM image of the cross section of the sintered body before grain boundary diffusion of Sample No. 4. [Figure 4] It is a SEM image of the cross section of the sintered body before grain boundary diffusion of Sample No. 63. [Figure 5] It is a SEM image of the cross section of the sintered body before grain boundary diffusion of Sample No. 41. [Figure 6] It is a SEM image of the cross section of the sintered body before grain boundary diffusion of Sample No. 41. [Figure 7] It is an image obtained by binarizing FIG. 2. [Figure 8] It is an image obtained by binarizing FIG. 4.

Mode for Carrying Out the Invention

[0022] Hereinafter, the present disclosure will be described based on the embodiments shown in the drawings.

[0023] <R-T-B-based permanent magnet> The R-T-B-based permanent magnet according to this embodiment has main phase particles containing crystal particles having an R2T 14 B-type crystal structure. Further, it has grain boundaries formed by two or more adjacent main phase particles. In particular, a linear grain boundary formed by two adjacent main phase particles is called a two-particle grain boundary, and a grain boundary formed by three or more main phase particles is called a grain boundary triple point. The grain boundary triple point is, for example, dot-shaped.

[0024] R-T-B-based permanent magnet and R2T 14 In the R2T

[0025] R-T-B-based permanent magnet and R2T 14The rare earth element included as R in the type B crystal structure may be Sc, Y, and lanthanides, or Y and lanthanides. The transition metal element included as T does not contain any rare earth elements. The transition metal element included as T may be an iron group element. Some of the boron included as B may be substituted with carbon.

[0026] There are no particular restrictions on the shape of the RTB-type permanent magnet according to this embodiment.

[0027] The RTB-type permanent magnet according to this embodiment can improve magnetic properties, particularly remanent magnetic flux density Br, coercivity HcJ, and aspect ratio Hk / HcJ, by incorporating multiple specific elements in specific ranges. Note that all of the above magnetic properties are measured at room temperature (23±1℃).

[0028] Specifically, Br may be 1400 mT or higher, and the coercivity HcJ may be 1900 kA / m or higher. Furthermore, Hk / HcJ may be 93.0% or higher.

[0029] Furthermore, the RTB-type permanent magnet according to this embodiment may have a concentration distribution in which the concentration of heavy rare earth elements decreases from the outside to the inside of the RTB-type permanent magnet 1. There are no particular restrictions on the type of heavy rare earth element. For example, it may be Dy or Tb, or it may be Tb.

[0030] Specifically, as shown in Figure 1, the rectangular parallelepiped RTB-type permanent magnet 1 according to this embodiment has a surface portion and a central portion. The heavy rare earth element content in the surface portion may be 2% or more, 5% or more, or 10% or more higher by mass than the heavy rare earth element content in the central portion. The surface portion refers to the surface of the RTB-type permanent magnet 1. For example, POINT C and C' in Figure 1 (the centroids of the opposing surfaces in Figure 1) are the surface portion. The central portion refers to the center of the RTB-type permanent magnet 1. For example, it refers to the portion that is half the thickness of the RTB-type permanent magnet 1. For example, POINT M in Figure 1 (the midpoint between POINT C and POINT C') is the central portion. Note that POINT C and C' in Figure 1 may be the centroid of the surface with the largest area among the surfaces of the RTB-type permanent magnet 1, and the centroid of the surface opposite to that surface.

[0031] Generally, rare earth elements are classified into light rare earth elements and heavy rare earth elements. In the RTB-type permanent magnet according to this embodiment, the light rare earth elements are Sc, Y, La, Ce, Pr, Nd, Sm, and Eu, and the heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0032] There are no particular limitations on the method for forming the aforementioned concentration distribution of heavy rare earth elements in the RTB-type permanent magnet according to this embodiment. For example, the concentration distribution of heavy rare earth elements can be formed within the RTB-type permanent magnet by grain boundary diffusion of heavy rare earth elements, as described later.

[0033] Furthermore, the main phase particles of the RTB-type permanent magnet according to this embodiment may be core-shell particles consisting of a core and a shell covering the core. The shell may contain heavy rare earth elements, and may contain Dy or Tb, or may contain Tb.

[0034] By incorporating heavy rare earth elements into the shell, the magnetic properties of RTB-type permanent magnets can be efficiently improved.

[0035] In this embodiment, the portion where the ratio of heavy rare earth elements to light rare earth elements (heavy rare earth elements / light rare earth elements (molar ratio)) is twice or more the ratio in the center of the main phase particles is defined as the shell. The ratio in the center of the main phase particles may, for example, be the ratio in the portion where the depth from the particle surface of the main phase particles is 30% or more of the particle size.

[0036] There are no particular restrictions on the thickness of the shell, but it may be less than 500 nm on average. Similarly, there are no particular restrictions on the particle size of the main phase particles, but it may be between 1.0 μm and 6.5 μm on average. When calculating the above averages, the cross-section of the RTB permanent magnet may be observed using a scanning electron microscope (SEM). An observation range large enough to accommodate 50 or more core-shell particles may be set. The thickness of the shell may be measured for all core-shell particles within the observation range and averaged. Alternatively, the particle size may be measured for all main phase particles within the observation range and averaged. The observation range may be, for example, 100 μm × 100 μm.

[0037] There are no particular restrictions on the method for making the main phase particles into the core-shell particles described above. For example, there is a method by grain boundary diffusion, which will be described later. Heavy rare earth elements diffuse into the grain boundaries, and these heavy rare earth elements replace the rare earth elements on the surface of the main phase particles, forming a shell with a high proportion of heavy rare earth elements, which becomes the core-shell particle described above.

[0038] The RTB-type permanent magnet according to this embodiment may contain at least one element selected from Nd and Pr as a light rare earth element, and at least one element selected from Dy and Tb as a heavy rare earth element. Furthermore, it is preferable that the RTB-type permanent magnet according to this embodiment contains at least Nd and Tb.

[0039] In this embodiment, the RTB-type permanent magnet may have a total content of rare earth elements other than Nd, Pr, Dy, and Tb of 0.3% by mass or less, with the total mass of the RTB-type permanent magnet being 100% by mass.

[0040] The total rare earth element content (TRE) in the RTB-type permanent magnet according to this embodiment is 28.50% by mass or more and 32.00% by mass or less, with the total mass of the RTB-type permanent magnet being 100% by mass. When the TRE is low, HcJ and Hk / HcJ tend to decrease. When the TRE is high, Hk / HcJ tend to decrease.

[0041] There are no particular restrictions on the total content of light rare earth elements in the RTB-type permanent magnet according to this embodiment, but it may be 28.30% by mass or more and 31.97% by mass or less, with the total mass of the RTB-type permanent magnet being 100% by mass.

[0042] When an RTB permanent magnet contains one or more elements selected from Nd and Pr, the Pr content may be 0.0% by mass or more and 10.0% by mass or less, 0.0% by mass or more and 8.5% by mass or less, or 0.0% by mass or more and 7.6% by mass or less.

[0043] The value obtained by dividing the Pr content by the total Nd and Pr content on a mass basis may be between 0 and 0.35.

[0044] Furthermore, in this embodiment, the RTB-type permanent magnet has a total heavy rare earth element content (TRH) of 0.03% to 0.20% by mass, with the total mass of the RTB-type permanent magnet being 100% by mass. If the amount of heavy rare earth elements is too low, the HcJ will not increase as easily compared to the case where heavy rare earth elements are not present. If the amount of heavy rare earth elements is too high, the raw material cost will increase. In addition, Br and Hk / HcJ will tend to decrease.

[0045] The Fe content constitutes the substantial remainder of the RTB-type permanent magnet. The statement that the Fe content constitutes the substantial remainder of the RTB-type permanent magnet means that, in the RTB-type permanent magnet, after excluding the aforementioned rare earth elements and the B, Zr, Cu, Al, Ga, Co, C, O, and N elements described later, the remainder is essentially Fe.

[0046] If the Fe content constitutes the substantial remainder of the RTB-type permanent magnet, elements other than rare earth elements, Fe, B, Zr, Cu, Al, Ga, Co, C, O, and N will not significantly affect the magnetic properties of the RTB-type permanent magnet.

[0047] For example, assuming the total mass of the RTB permanent magnet is 100% by mass, the content of elements other than rare earth elements, Fe, B, Zr, Cu, Al, Ga, Co, C, O, and N may be 0.10% by mass or less each, and the total may be 1.0% by mass or less. When the content of elements other than rare earth elements, Fe, B, Zr, Cu, Al, Ga, Co, C, O, and N is 0.10% by mass or less each, and the total is 1.0% by mass or less, the Fe content is the substantial remainder of the RTB permanent magnet.

[0048] The B content in the RTB-type permanent magnet according to this embodiment is 0.88% by mass or more and 1.00% by mass or less, with the total mass of the RTB-type permanent magnet being 100% by mass. It may be 0.90% by mass or more and 1.00% by mass or less, or 0.92% by mass or more and 1.00% by mass or less. If the amount of B is low, the Hk / HcJ ratio tends to decrease. If the amount of B is high, the HcJ ratio tends to decrease.

[0049] The RTB-type permanent magnet according to this embodiment further contains Zr. The Zr content is 0.01% by mass or more and 0.50% by mass or less, with the total mass of the RTB-type permanent magnet being 100% by mass. It may be 0.04% by mass or more and 0.50% by mass or less, or 0.05% by mass or more and 0.50% by mass or less. If Zr is not included, HcJ and Hk / HcJ tend to decrease. If Zr is present in large quantities, Br tends to decrease.

[0050] The RTB-type permanent magnet according to this embodiment further contains Cu. The Cu content is 0.04% by mass or more and 0.50% by mass or less, with the total mass of the RTB-type permanent magnet being 100% by mass. It may be 0.08% by mass or more and 0.50% by mass or less, or 0.08% by mass or more and 0.30% by mass or less. If the amount of Cu is low, HcJ tends to decrease. If the amount of Cu is high, Br tends to decrease. Also, whether the amount of Cu is high or low, Hk / HcJ tends to decrease.

[0051] The RTB-type permanent magnet according to this embodiment may further contain Al. The Al content is 0% to 0.60% by mass, with the total mass of the RTB-type permanent magnet being 100% by mass. It may also be 0% to 0.40% by mass. The RTB-type permanent magnet does not need to contain Al, but the less Al there is, the more likely HcJ will decrease. Also, if there is a lot of Al, the more likely Br will decrease.

[0052] The RTB-type permanent magnet according to this embodiment may further contain Ga. The Ga content is 0% to 0.80% by mass, with the total mass of the RTB-type permanent magnet being 100% by mass. It may also be 0.05% to 0.70% by mass. The RTB-type permanent magnet does not need to contain Ga, but the less Ga there is, the more likely HcJ will decrease. Conversely, if there is a lot of Ga, the more likely Br will decrease.

[0053] The RTB-type permanent magnet according to this embodiment may further contain Co. The Co content is 0% to 3.50% by mass, based on 100% of the total mass of the RTB-type permanent magnet. It may also be 0.2% to 3.20% by mass, or 0.3% to 3.20% by mass. While RTB-type permanent magnets do not necessarily need to contain Co, the lower the Co content, the more likely the corrosion resistance will decrease. Also, a high Co content results in higher costs.

[0054] The RTB-type permanent magnet according to this embodiment further contains carbon (C). The C content is 0.05% by mass or more and 0.12% by mass or less, based on the total mass of the RTB-type permanent magnet as 100% by mass. It may also be 0.05% by mass or more and 0.11% by mass or less. If the amount of C is low, the HcJ tends to decrease. If the amount of C is high, the HcJ and Hk / HcJ tend to decrease.

[0055] The RTB-type permanent magnet according to this embodiment further contains oxygen (O). The O content is 0.11% by mass or more and 0.30% by mass or less, based on the total mass of the RTB-type permanent magnet as 100% by mass. It may also be 0.13% by mass or more and 0.29% by mass or 0.13% by mass or more and 0.26% by mass or less. If the amount of O is low, the HcJ tends to decrease. If the amount of O is high, the Br and HcJ tend to decrease.

[0056] The RTB-type permanent magnet according to this embodiment further contains nitrogen (N). The N content is 0.015% by mass or more and 0.07% by mass or less, based on the total mass of the RTB-type permanent magnet as 100% by mass. It may also be 0.02% by mass or more and 0.07% by mass or less. Too much or too little N can easily lead to a decrease in HcJ.

[0057] The various components contained in the RTB-type permanent magnet according to this embodiment can be measured using conventionally known methods. The amounts of various elements can be measured, for example, by X-ray fluorescence analysis and inductively coupled plasma emission spectroscopy (ICP analysis). The O content can be measured, for example, by inert gas fusion-nondispersive infrared absorption spectroscopy. The C content can be measured, for example, by combustion in an oxygen stream-infrared absorption spectroscopy. The N content can be measured, for example, by inert gas fusion-thermal conductivity spectroscopy.

[0058] There are no particular restrictions on the shape of the RTB-type permanent magnet according to this embodiment. For example, shapes such as a rectangular parallelepiped or a C-shape can be used.

[0059] The following describes in detail a method for manufacturing an RTB-type permanent magnet according to this embodiment, specifically a method for manufacturing an RTB-type sintered magnet. However, the method for manufacturing an RTB-type permanent magnet is not limited to this, and other known methods may be used.

[0060] [Preparation process for raw material powder] The raw material powder can be prepared by known methods. In this embodiment, the case of a single alloy method using one alloy will be described, but the so-called two-alloy method, in which two or more alloys with different compositions are mixed to prepare the raw material powder, may also be used.

[0061] First, the raw material alloy for the RTB-type permanent magnet is prepared (alloy preparation step). In the alloy preparation step, the raw material metal corresponding to the composition of the RTB-type permanent magnet according to this embodiment is melted by a known method, and then cast to produce a raw material alloy having the desired composition.

[0062] As raw material metals, for example, elemental rare earth elements, elemental metallic elements such as Fe, or compounds consisting of multiple elements (e.g., ferroboron) can be used as appropriate. There are no particular restrictions on the casting method for casting the raw material alloy from the raw material metal. A strip casting method may be used to obtain RTB-type permanent magnets with high magnetic properties. The obtained raw material alloy may be homogenized using known methods as needed.

[0063] After preparing the raw material alloy, it is crushed (crushing step). The atmosphere in each step from the crushing step to the sintering step can be kept at a low oxygen concentration from the viewpoint of obtaining high magnetic properties. For example, the oxygen concentration in the atmosphere at each step may be 200 ppm or less (0.02% or less). However, the oxygen concentration in the atmosphere may be increased in one of the steps before forming the finely crushed powder into the desired shape in order to control the oxygen content of the alloy powder. Details will be described later.

[0064] The following description outlines a two-stage grinding process, consisting of a coarse grinding stage where the particle size is reduced to several hundred micrometers to several millimeters, and a fine grinding stage where the particle size is reduced to several micrometers. However, the process may also be carried out in a single stage, consisting only of the fine grinding stage.

[0065] In the coarse grinding process, the material is coarsely ground until the particle size is approximately several hundred micrometers to several millimeters. This yields a coarse powder. There are no particular limitations on the coarse grinding method; it can be carried out using known methods such as hydrogen storage grinding.

[0066] Hydrogen storage pulverization involves two processes: hydrogen storage, in which hydrogen is absorbed into the alloy, and hydrogen dissolution, in which the hydrogen-storing alloy is dehydrogenated to dissolve it. The crude powder obtained by hydrogen dissolution is heat-treated in an atmosphere with an oxygen concentration of 0.5% to 23%, thereby controlling the oxygen content of the final alloy powder. In some cases, the nitrogen content can also be controlled in conjunction with the oxygen content. The heat treatment temperature may be between 50°C and 200°C. The heat treatment time may be between 5 minutes and 4 hours. The heat treatment of the crude powder may also be carried out in a stirring device equipped with a screw or the like.

[0067] Next, the coarse powder is finely ground until the average particle size is about a few micrometers (fine grinding step). This yields fine powder (raw material powder). The average particle size of the fine powder may be 1 μm to 10 μm, 2 μm to 6 μm, or 2 μm to 4 μm.

[0068] There are no particular restrictions on the method of fine grinding. For example, it can be carried out using a jet mill.

[0069] By controlling the oxygen concentration in the atmosphere during fine grinding to between 0.01% and 0.30%, the O content of the final alloy powder can be controlled. The oxygen concentration in the atmosphere during fine grinding may also be between 0.02% and 0.30%, or between 0.03% and 0.30%. Furthermore, controlling the O content may also allow for control of the N content.

[0070] In controlling the oxygen content of the final alloy powder, it is preferable to appropriately supply oxygen gas, or a mixture of noble gas and oxygen gas, so that the oxygen concentration in the atmosphere during fine grinding does not fall below the lower limit of the above-mentioned numerical range of oxygen concentration. Even if the oxygen concentration in the atmosphere at the start of fine grinding is above the lower limit of the above-mentioned numerical range of oxygen concentration, if sufficient oxygen is not supplied to the atmosphere during fine grinding, the oxygen concentration in the atmosphere will decrease. This is because the powder absorbs oxygen during fine grinding.

[0071] By performing the fine grinding in a jet mill with a mixed gas atmosphere of a noble gas and oxygen gas, the oxygen content of the final alloy powder can be controlled. In addition, the nitrogen content can sometimes be controlled along with the oxygen content. There are no particular restrictions on the type of noble gas. Examples include argon gas, helium gas, and a mixed gas of argon gas and helium gas.

[0072] When the aforementioned coarsely ground powder is finely ground, by adding various grinding aids such as lauric acid amide and oleic acid amide, it is possible to obtain a finely ground powder in which the crystal particles tend to orient in a specific direction when molded under pressure in a magnetic field. Furthermore, by changing the amount of grinding aid added, the carbon (C) and nitrogen (N) content in the RTB-type permanent magnet can be controlled.

[0073] Furthermore, the oxygen content can be controlled by, for example, heat-treating the coarse powder with an oxygen concentration of 0.5% to 23% in the atmosphere, as described above, and then performing the fine grinding using a mixed gas of noble gas and oxygen gas, or a noble gas, in the atmosphere inside the jet mill. This allows for the control of the oxygen content in the final alloy powder. In some cases, the nitrogen content can also be controlled in conjunction with the oxygen content. There are no particular restrictions on the type of noble gas. Examples include argon gas, helium gas, and a mixed gas of argon gas and helium gas.

[0074] [Molding process] In the molding process (compression molding process), the finely ground powder is molded into the desired shape. There are no particular restrictions on the molding method. In this embodiment, the finely ground powder is filled into a mold and pressurized in a magnetic field. The resulting molded body has crystal particles oriented in a specific direction, thus yielding an RTB-type permanent magnet with a higher Br.

[0075] The pressure applied during molding can be between 20 MPa and 300 MPa. The applied magnetic field can be 950 kA / m or higher, or between 950 kA / m and 1600 kA / m. The applied magnetic field is not limited to a static magnetic field; a pulsed magnetic field can also be used. Furthermore, a combination of a static magnetic field and a pulsed magnetic field can be used.

[0076] In addition to dry molding, which involves molding the finely ground powder as is, as described above, wet molding can also be applied, which involves molding a slurry in which the finely ground powder is dispersed in a solvent such as oil.

[0077] There are no particular restrictions on the shape of the molded body obtained by molding the finely ground powder. Furthermore, the density of the molded body at this point is 4.0 Mg / m³. 3 ~4.3Mg / m 3 It can be done this way.

[0078] [Sintering process] The sintering process involves sintering a molded body in a vacuum or inert gas atmosphere to obtain a sintered body. The sintering conditions need to be adjusted based on various factors, including composition, grinding method, particle size, and particle size distribution. For example, the molded body can be sintered by heating it in a vacuum or inert gas atmosphere at a temperature between 1000°C and 1200°C for 1 to 20 hours. By sintering under these conditions, a high-density sintered body can be obtained. In this embodiment, at least 7.45 Mg / m³ 3 A sintered body with the above density is obtained. The density of the sintered body is 7.50 Mg / m³. 3 That's fine too.

[0079] [Statute of Limitations Treatment Process] The aging process is a process of heat-treating (aging) the sintered body at a temperature lower than the sintering temperature. There are no particular restrictions on whether or not to perform the aging process, nor are there any particular restrictions on the number of times the aging process is performed. The following describes an embodiment in which the aging process is performed twice, but if the aging process is performed only once, the aging process in which this aging process is performed will be referred to as the first aging process described later.

[0080] The first aging process is designated as the first aging process, and the second aging process as the second aging process. The aging temperature for the first aging process is T1, and the aging temperature for the second aging process is T2.

[0081] In the RTB-type permanent magnet according to this embodiment, the dispersion state of the grain boundary triple point, described later, changes depending on the conditions of the first aging process. There are no particular restrictions on the atmosphere of the first aging process. For example, it may be an argon atmosphere, a vacuum atmosphere, or a reduced-pressure argon atmosphere obtained by flowing argon into a vacuum. There are no particular restrictions on T1. T1 may be 700°C or more and 1000°C or less, 700°C or more and 950°C or less, or 850°C or more and 950°C or less. There are no particular restrictions on the aging time of the first aging process. The aging time of the first aging process may be 1.0 hour or more and 15 hours or less, 1.0 hour or more and 10 hours or less, or 1.5 hours or more and 10 hours or less.

[0082] The RTB-based permanent magnet according to this embodiment has a composition within a predetermined range, particularly the carbon, oxygen, and nitrogen content being within a predetermined range. When the first aging process is carried out on such an RTB-based permanent magnet under the above-mentioned conditions, the composition of the liquid phase at the grain boundary triple point is suitably controlled during the first aging process. The viscosity of the liquid phase becomes suitable. As a result, a network structure is formed connecting the grain boundary triple points, and the liquid phase is supplied from the grain boundary triple point to the two-particle grain boundary. Then, while maintaining the volume ratio of the main phase, the dispersion state of the grain boundary triple point becomes suitable, and the two-particle grain boundary becomes thicker. As a result, the magnetic properties are more easily improved.

[0083] The first aging process may be performed before or after the grain boundary diffusion process described later. Performing the first aging process before the grain boundary diffusion process described later makes it easier to control the equivalent circle diameter and total area ratio of the low-melting-point grain boundary phase. In addition, the first aging process may also serve as the heat treatment in the grain boundary diffusion process described later.

[0084] There are no particular restrictions on T2 and the aging time in the second aging process. T2 can be between 450°C and 700°C. The aging time can be between 1 hour and 10 hours.

[0085] The second aging process may be performed after the first aging process and before the grain boundary diffusion process described later. Alternatively, the second aging process may be performed after the grain boundary diffusion process described later.

[0086] [Processing step (before grain boundary diffusion)] If necessary, the sintered body according to this embodiment may include a step of processing it into a desired shape. Examples of processing methods include shaping such as cutting and grinding, and chamfering such as barrel polishing.

[0087] [Grain boundary diffusion process] The grain boundary diffusion process can be carried out by attaching a diffusion material to the surface of the sintered body and heating the sintered body to which the diffusion material is attached. This process yields an RTB-type permanent magnet.

[0088] (Diffusion material application process) In this embodiment, there are no particular restrictions on the type of diffusion material. The diffusion material may contain a hydride of a heavy rare earth element (e.g., Tb), the diffusion material may contain a heavy rare earth element and Cu, or the diffusion material may be a heavy rare earth element in its elemental form (e.g., metallic Tb).

[0089] The diffusion material may be a slurry containing a solvent in addition to the hydrides of heavy rare earth elements mentioned above. The solvent in the slurry may be a solvent other than water. For example, it may be an organic solvent such as alcohol, aldehyde, or ketone. Furthermore, the diffusion material may contain a binder. There are no particular restrictions on the type of binder. For example, a resin such as acrylic resin may be included as the binder. Including a binder makes it easier for the diffusion material to adhere to the surface of the sintered body.

[0090] The diffusion agent may be a paste containing a solvent and a binder in addition to the hydrides of heavy rare earth elements mentioned above. The paste has fluidity and high viscosity. The viscosity of the paste is higher than that of the slurry.

[0091] Before the diffusion treatment described later, the sintered body to which the slurry or paste is attached may be dried and the binder removed in order to remove the solvent.

[0092] The holding temperature during drying may be 200°C or lower, and the holding time may be between 3 minutes and 1 hour.

[0093] The holding temperature during binder removal may be between 200°C and 800°C, and the holding time may be between 10 minutes and 10 hours. In particular, when the holding temperature during binder removal is high, grain boundary diffusion of heavy rare earth elements may proceed during binder removal. The atmosphere during binder removal should be in an inert gas environment. By removing the binder from the sintered body to which the slurry or paste is attached, the formation of carbides of heavy rare earth elements on the surface of the magnet substrate can be suppressed, and the amount of heavy rare earth elements used can be further reduced.

[0094] Alternatively, a heavy rare earth element (e.g., metallic Tb) can be used as a diffuser by sputtering, and the elemental heavy rare earth element may be attached to the surface of the sintered body. There are no particular restrictions on the equipment used for sputtering, but a magnetron sputter may be used. In particular, when the amount of diffuser to be attached is small, it is preferable to use a method of attaching the diffuser by sputtering.

[0095] (Heating process) In the heating step of the grain boundary diffusion process, as the temperature rises, the grain boundary phase (especially the low-melting-point grain boundary phase) with a high concentration of rare earth elements present at the grain boundaries of the magnet substrate (sintered body) becomes a liquid phase. The diffusion material dissolves into this liquid phase, causing the components of the diffusion material to diffuse from the surface of the magnet substrate into the interior of the magnet substrate. Alternatively, when the diffusion material (for example, elemental heavy rare earth elements) is attached to the surface of the sintered body by sputtering, the components of the diffusion material may be diffused by heating the substrate on which the sintered body is placed.

[0096] The diffusion process in the grain boundary diffusion step according to this embodiment may be carried out continuously from the removal of the binder described above. Alternatively, after the removal of the binder, the material may be cooled to room temperature and then reheated before the diffusion process is carried out. The holding temperature during the diffusion process may be 700°C or higher and 1000°C or lower. In the grain boundary diffusion step, the temperature of the magnet substrate may be gradually increased from a temperature lower than the diffusion process temperature to the diffusion process temperature.

[0097] The time for which the substrate temperature is maintained at the diffusion treatment temperature (diffusion treatment time) may be, for example, 1 hour or more and 50 hours or less. The atmosphere surrounding the substrate during the diffusion treatment process may be a non-oxidizing atmosphere. A non-oxidizing atmosphere may be, for example, a noble gas such as argon. The pressure of the atmosphere surrounding the magnetic substrate during the diffusion process may be 1 kPa or less. When the diffusion material is a hydride of a heavy rare earth element, such a reduced-pressure atmosphere promotes the dehydrogenation reaction of the hydride. As a result, the dissolution of the diffusion material into the liquid phase proceeds more easily.

[0098] The above-described second aging process may be performed after the grain boundary diffusion process. Furthermore, the above-described first aging process may be performed before the grain boundary diffusion process. By performing the above-described first aging process before the grain boundary diffusion process and the above-described second aging process after the grain boundary diffusion process, it becomes easier to suitably control the equivalent circle diameter and total area ratio of the low-melting-point grain boundary phase, and it becomes easier to improve the magnetic properties of the final RTB-type sintered magnet.

[0099] [Processing steps (after grain boundary diffusion)] After the grain boundary diffusion process, polishing may be performed to remove any remaining diffusion material from the surface of the RTB permanent magnet. Other processing may also be performed on the RTB permanent magnet. For example, shaping such as cutting and grinding, or surface processing such as chamfering by barrel polishing may be performed. Furthermore, polishing may be performed before or after the second aging process.

[0100] In this embodiment, processing steps are performed before and after grain boundary diffusion, but these steps are not necessarily required.

[0101] In particular, RTB-type permanent magnets after grain boundary diffusion tend to have a concentration distribution in which the concentration of heavy rare earth elements decreases from the outside to the inside of the RTB-type permanent magnet. Furthermore, the main phase particles contained in RTB-type permanent magnets after grain boundary diffusion tend to have the core-shell structure described above.

[0102] The RTB-based permanent magnet obtained in this manner according to this embodiment has the desired properties despite having a relatively low content of heavy rare earth elements. Specifically, it has high Br, HcJ, and Hk / HcJ ratios.

[0103] The RTB-type permanent magnet according to this embodiment, obtained by the above method, becomes a magnetized RTB-type permanent magnet by magnetizing it.

[0104] The following explains why the RTB-type permanent magnet according to this embodiment possesses the desired properties despite having a relatively low content of heavy rare earth elements.

[0105] Sintered bodies before grain boundary diffusion (hereinafter, sintered bodies before grain boundary diffusion may be referred to as substrates) with compositions within the above range, particularly those with carbon, oxygen, and nitrogen content within the above range, tend to have thicker two-particle grain boundaries.

[0106] Substrates produced by the above manufacturing method, primarily by controlling the amount of oxygen, tend to have thicker two-particle grain boundaries.

[0107] Specifically, the substrate, which is the precursor of the RTB-type permanent magnet according to this embodiment, has a two-particle grain boundary that is thick enough to be visible in the cross-sectional image (SEM image) obtained using SEM, as shown in Figures 2 to 4. Figure 2 is an SEM image at a magnification of 2500x of the substrate of sample No. 4 in the example described later. Figure 3 is an SEM image at a magnification of 5000x of the substrate of sample No. 4 in the example described later. Figure 4 is an SEM image at a magnification of 2500x of the substrate of sample No. 63 in the example described later. Note that all SEM images in this embodiment are backscattered electron images.

[0108] As a result of the thickness of the two-particle grain boundary in the substrate, to the point where the interface of the two-particle grain boundary can be observed, the HcJ of the substrate increases. Furthermore, even with a reduction in the diffusion of heavy rare earth elements, the magnetic properties of the RTB-type permanent magnet obtained by grain boundary diffusion are improved.

[0109] Figure 5 is an SEM image at 2500x magnification of the substrate of sample No. 41, a comparative example described later. Figure 6 is an SEM image at 5000x magnification of the substrate of sample No. 41, a comparative example described later. In either image, the interface of the two-particle grain boundary cannot be seen. In such cases, the width of the two-particle grain boundary can be confirmed using a TEM (transmission electron microscope). The width of the two-particle grain boundary is actually confirmed to be approximately 5 nm.

[0110] The width of the two-particle grain boundary that can be confirmed in the SEM image is generally 15 nm or more. The width of the two-particle grain boundary may be between 15 nm and 50 nm. Furthermore, if there is an observation target in which five or more two-particle grain boundary interfaces with a length of 0.5 μm or more can be confirmed in an arbitrarily selected 20 μm × 15 μm area within the field of view of a sufficiently large SEM image observed at a magnification of 5000x, the two-particle grain boundary of the sintered body may be considered sufficiently thick.

[0111] Furthermore, the RTB-type permanent magnet according to this embodiment has a composition within the above range, particularly the carbon, oxygen, and nitrogen content within the above range, and by performing a predetermined heat treatment (particularly a predetermined first aging treatment) under conditions within the above range, the dispersion state of the grain boundary triple point becomes favorable. This makes it easier to thicken the two-particle grain boundary while maintaining the volume ratio of the main phase. As a result, it is thought that the magnetic properties are more easily improved.

[0112] To evaluate the dispersion state of grain boundary triple points, rare earth oxide phases and low-melting-point grain boundary phases are extracted from all grain boundary triple points within the field of view of the SEM image. Low-melting-point grain boundary phases refer to grain boundary phases other than the rare earth oxide phase, which has a relatively high melting point.

[0113] The rare earth oxide phase may contain nitrogen and / or carbon in addition to rare earth elements and oxygen. There are no particular restrictions on the composition of the rare earth oxide phase. For example, the content of rare earth elements in the rare earth oxide phase may be 30 to 70 at%. The content of oxygen in the rare earth oxide phase may be 10 to 60 at%. The content of carbon in the rare earth oxide phase may be 0 to 40 at%. The content of nitrogen in the rare earth oxide phase may be 0 to 30 at%. Furthermore, the rare earth oxide phase may be composed mainly of rare earth elements, oxygen, carbon, and nitrogen. "Composed mainly of rare earth elements, oxygen, carbon, and nitrogen" means that the total content of elements other than rare earth elements, oxygen, carbon, and nitrogen is 0 at% or more and 20 at% or less.

[0114] The total area ratio of low-melting-point grain boundary phases in an RTB-type permanent magnet can be calculated by dividing the total area of ​​low-melting-point grain boundary phases contained in one cross-section of the RTB-type permanent magnet (i.e., the total area of ​​grain boundary phases other than rare-earth oxide phases) by the area of ​​that cross-section. The area of ​​that cross-section is calculated from the magnification and number of pixels of the SEM image.

[0115] Furthermore, the equivalent circular diameter of each low-melting-point grain boundary phase contained in one cross-section of an RTB-type permanent magnet can be calculated, and the average equivalent circular diameter of the low-melting-point grain boundary phases can be calculated by arithmetic mean of the equivalent circular diameters of the individual low-melting-point grain boundary phases. The equivalent circular diameter of a low-melting-point grain boundary phase is a parameter obtained by converting the area of ​​the low-melting-point grain boundary phase into the diameter of a circle with the same area.

[0116] These parameters can be used to evaluate the dispersion state of grain boundary triple points.

[0117] The reason for not considering the total area of ​​the rare earth oxide phases and the equivalent circular diameter of each rare earth oxide phase is that the rare earth oxide phases are considered to contribute little to the dispersion of the grain boundary triple points. The reason why the rare earth oxide phases are considered to contribute little to the dispersion of the grain boundary triple points is that they have a high melting point, and therefore do not easily become liquid and flow due to the heat treatment in the first aging treatment or grain boundary diffusion described above.

[0118] There are no particular restrictions on the method for distinguishing between the low-melting-point grain boundary phase (grain boundary phase other than the rare-earth oxide phase) and the parts other than the low-melting-point grain boundary phase (main phase and rare-earth oxide phase). For example, a brightness-based binarization process may be performed on the SEM image. By performing a binarization process on the SEM image, the SEM image becomes black and white. There are no particular restrictions on the type of image processing software used for the binarization process. Any image processing software that can determine the shape of the low-melting-point grain boundary phase after binarization is acceptable.

[0119] The threshold for binarization is set between the low-melting-point grain boundary phase and the parts other than the low-melting-point grain boundary phase. The threshold can be set automatically using image processing software or by visually inspecting the SEM image. Since the image contrast differs between the parts other than the low-melting-point grain boundary phase (main phase and rare-earth oxide phase) and the low-melting-point grain boundary phase, they can be clearly distinguished by binarization.

[0120] There are no particular restrictions on the total area ratio of the low-melting-point grain boundary phase. It may be between 1.5% and 7.5%, or between 3.5% and 6.8%. There are no particular restrictions on the average equivalent circle diameter of the low-melting-point grain boundary phase. It may be between 0.40 μm and 1.00 μm, or between 0.46 μm and 0.92 μm. The dispersion state of the grain boundary triple points can be said to be good when the total area ratio of the low-melting-point grain boundary phase and the average equivalent circle diameter of the low-melting-point grain boundary phase are within the above ranges.

[0121] The RTB-type permanent magnet according to this embodiment is suitably used in applications such as motors and generators. [Examples]

[0122] The present disclosure will be described below with reference to more detailed examples, but the disclosure is not limited to these examples.

[0123] (Fabrication of RTB-type permanent magnets) Raw alloys were prepared using the strip-casting method so that the final RTB-type permanent magnet would have the composition of each sample shown in Tables 1 to 9. Tb was not included in the raw alloy, but only in the diffusion paste described later. Other elements not listed in Tables 1 to 9, such as H, Si, Ca, La, Ce, and Cr, may be detected. Si may be mainly introduced from the ferroboron raw material and the crucible during alloy melting. Ca, La, and Ce may be introduced from rare earth raw materials. Cr may be introduced from electrolytic iron. In Tables 1 to 9, the Fe content is indicated as "bal." to show that the Fe content is the actual remainder when the entire RTB-type permanent magnet containing these other elements is considered as 100 mass%.

[0124] Next, hydrogen gas was flowed over the raw material alloy at room temperature for 1 hour to allow hydrogen to be absorbed. Then, the atmosphere was switched to Ar gas, and a dehydrogenation treatment was performed at 500°C for 1 hour, and the raw material alloy was pulverized to absorb hydrogen and obtain a coarse powder.

[0125] Next, the coarse powder obtained by the stirring device having a screw was charged. Then, heat treatment was carried out while stirring the coarse powder in an atmosphere with an oxygen concentration of 0.5% or more and 23% or less. The heat treatment temperature was 140 °C and the heat treatment time was 2.5 hours. By changing the oxygen concentration in the atmosphere, the oxygen concentration of the alloy powder obtained after fine pulverization was controlled.

[0126] Next, 0.1% by mass of oleic acid amide was added as a pulverization aid to the coarse powder after heat treatment, and it was mixed using a Nauta mixer.

[0127] Next, it was finely pulverized in a nitrogen stream using a collision plate type jet mill device to obtain fine powder (raw material powder) with an average particle size of about 3.0 μm. The average particle size is the average particle size D50 measured by a laser diffraction type particle size distribution meter.

[0128] The obtained fine powder was formed in a magnetic field to produce a formed body. The applied magnetic field at this time was a static magnetic field of 1200 kA / m. Also, the pressure during forming was 120 MPa. The magnetic field application direction and the pressurization direction were made orthogonal.

[0129] Next, the formed body was sintered to obtain a sintered body. The sintering conditions vary depending on the composition and the like, but it was held for 4 hours within the range of 1030 °C to 1070 °C. The sintering atmosphere was a vacuum. The sintering density at this time was 7.51 Mg / m 3 ~7.55 Mg / m 3 and was in the range. Then, the first aging treatment was performed while flowing Ar at atmospheric pressure (1 atm). The first aging treatment temperature T1 was 900 °C and the first aging treatment time was 2 hours. From the above, sintered bodies of each sample shown in Tables 1 to 9 were produced by grain boundary diffusion.

[0130] (Production of diffusion material paste) Next, a diffusion material paste used for grain boundary diffusion other than Sample Nos. 71a and 72 was produced.

[0131] First, hydrogen was absorbed into 99.9% pure metal Tb by flowing hydrogen gas through it at room temperature. Next, the atmosphere was switched to Ar gas, and dehydrogenation treatment was performed at 500°C for 1 hour to hydrogen-absorbed and pulverized the metal Tb. Then, as a pulverizing aid, 0.05% by mass of zinc stearate was added per 100% by mass of metal Tb, and mixed using a Nauta mixer. After that, fine pulverization was performed using a jet mill in an atmosphere containing 3000 ppm of oxygen to obtain a finely pulverized powder of Tb hydride with an average particle size of approximately 10.0 μm.

[0132] A diffusion paste was prepared by kneading 60 parts by mass of finely ground Tb hydride powder, 10 parts by mass of metallic Cu powder, 25 parts by mass of alcohol, and 5 parts by mass of acrylic resin. The alcohol acts as a solvent, and the acrylic resin acts as a binder.

[0133] (Application and heat treatment of diffusion paste) The above sintered body was processed to a size of 11 mm (length) x 11 mm (width) x 4.2 mm (thickness in the easy magnetization axis direction: 4.2 mm). Then, it was immersed for 3 minutes in a mixed solution of nitric acid and ethanol (100 parts by mass of ethanol and 3 parts by mass of nitric acid), followed by an etching treatment of immersion in ethanol for 1 minute. This etching treatment, consisting of immersion in the mixed solution for 3 minutes followed by immersion in ethanol for 1 minute, was performed twice.

[0134] Next, the diffusion paste described above was applied to the entire surface of the sintered body after etching. The amount of diffusion paste applied was adjusted so that the Tb content in the final RTB-type permanent magnet would be the value shown in Tables 1 to 9.

[0135] Sample No. 71 underwent processing and etching, but the diffusion paste was not applied.

[0136] Samples No. 71a and 72 will be described below.

[0137] In samples No. 71a and 72, metal Tb was deposited onto the sintered body after the above processing and etching treatments by sputtering with metal Tb as the target. Magnetron sputtering was used for sputtering.

[0138] The amount of Tb deposited on the sintered body was adjusted so that the Tb content in the final RTB-type permanent magnet would be the values ​​shown in Tables 1 to 9.

[0139] Next, the sintered bodies were dried. Specifically, the sintered bodies coated with the diffusion paste (excluding the sintered body without diffusion paste in sample No. 71, and the sintered bodies in samples No. 71a and 72 to which Tb was attached by sputtering) were left in the air in a 160°C oven for 45 minutes to remove the solvent from the diffusion paste.

[0140] Next, the binder was removed from the sintered bodies. Specifically, the sintered bodies with the diffusion paste dried (excluding the sintered body without diffusion paste in sample No. 71, and the sintered bodies with Tb attached by sputtering in samples No. 71a and 72) were left in an Ar gas atmosphere in a 400°C oven for 3 hours to remove any remaining binder in the dried diffusion material. Then, heavy rare earth elements were diffused at grain boundaries by heating at 900°C for 30 hours while flowing Ar at atmospheric pressure (1 atm). Furthermore, a second aging treatment was performed by heating at 500°C for 1 hour while flowing Ar at atmospheric pressure (1 atm). From the above, RTB-type permanent magnets for each sample shown in Tables 1 to 9 were obtained.

[0141] After scraping 0.1 mm off each surface of an RTB-type permanent magnet, its composition, microstructure, elemental distribution, and magnetic properties were evaluated.

[0142] RTB-type permanent magnets were processed vertically to a size of 11 mm (length) x 11 mm (width) x 4.2 mm (thickness) (with the easy magnetization axis direction being 4.2 mm), and their magnetic properties were evaluated at room temperature using a BH tracer. Before measuring the magnetic properties, the RTB-type permanent magnets were magnetized with a pulsed magnetic field of 4000 kA / m. Due to the thinness of the RTB-type permanent magnets, three magnets were stacked to evaluate their magnetic properties. In this example, Hk / HcJ was calculated by taking the magnetic field at which the magnetization reached 90% of Br in the second quadrant (JH demagnetization curve) of the magnetization J-magnetic field H curve as Hk (kA / m), and multiplying by Hk / HcJ × 100 (%).

[0143] In this embodiment, a Br value of 1400 mT or higher for the RTB permanent magnet was considered good, and a value of 1430 mT or higher was considered even better. A HcJ value of 1900 kA / m or higher for the RTB permanent magnet was considered good, a value of 1915 kA / m or higher was considered even better, and a value of 1950 kA / m or higher was considered particularly good. A Hk / HcJ value of 93.0% or higher for the RTB permanent magnet was considered good, and a value of 95.0% or higher was considered even better.

[0144] The cross-section of the sintered body (substrate) before grain boundary diffusion was observed using a scanning electron microscope (SEM). The measurement conditions were an acceleration voltage of 5.0 kV, and a 20 μm × 15 μm area was arbitrarily selected within the field of view of a sufficiently large SEM image observed at a magnification of 5000x. A good result was defined as having five or more two-particle grain boundary interfaces with a length of 0.5 μm or more. A poor result was defined as not having five or more two-particle grain boundary interfaces with a length of 0.5 μm or more. The results are shown in Tables 1 to 9.

[0145] [Table 1]

[0146] [Table 2]

[0147] [Table 3]

[0148] [Table 4]

[0149] [Table 5]

[0150] [Table 6]

[0151] [Table 7]

[0152] [Table 8]

[0153] [Table 9]

[0154] Tables 1 to 9 show that in each example, where all compositions were within a specific range, a sufficient number of two-particle grain boundary interfaces were observed before grain boundary diffusion. Furthermore, each example yielded good magnetic properties.

[0155] Table 1 shows that sample No. 1, which had too little TRE (total content of rare earth elements), showed a decrease in HcJ and Hk / HcJ. Sample No. 7, which had too much TRE, also showed a decrease in Hk / HcJ.

[0156] Table 2 shows that sample No. 11, which had too little B content, showed a decrease in Hk / HcJ. Sample No. 16, which had too much B content, also showed a decrease in HcJ.

[0157] Table 3 shows that sample No. 21, which did not contain Zr, showed a decrease in HcJ and Hk / HcJ. Sample No. 28, which had too much Zr, showed a decrease in Br.

[0158] Table 4 shows that sample No. 31, which had too little Cu content, showed a decrease in HcJ. Sample No. 36, which had too much Cu content, showed a decrease in Br.

[0159] Table 5 shows that in both sample No. 41, which had too little oxygen content, and sample No. 47, which had too much oxygen content, the two-particle grain boundary interface was not sufficiently observed in the substrate. Furthermore, sample No. 41 showed a decrease in HcJ, while sample No. 47 showed decreases in both Br and HcJ.

[0160] Table 6 shows that in both sample No. 51, which had too little carbon content, and sample No. 56, which had too much carbon content, the two-particle grain boundary interface was not sufficiently observed in the substrate. Furthermore, sample No. 51 showed a decrease in HcJ, while sample No. 56 showed a decrease in both HcJ and Hk / HcJ.

[0161] Table 7 shows that in both sample No. 61, which had too little N content, and sample No. 66, which had too much N content, the two-particle grain boundary interface was not sufficiently observed in the substrate. Furthermore, HcJ decreased in both sample No. 61 and sample No. 66.

[0162] Table 8 shows that sample No. 71, in which Tb was not diffused at the grain boundaries, showed a decrease in HcJ. Sample No. 76, in which TRH (total content of heavy rare earth elements) was too high, did not sufficiently reduce the amount of heavy rare earth elements. Furthermore, its Hk / HcJ ratio was lower compared to each example where TRH was sufficiently low.

[0163] Table 9 shows that for sample No. 41, which had too little O content, and sample No. 51, which had too little C content, even when the TRE was increased to a size similar to sample No. 75, the two-particle grain boundary interface was not sufficiently observed on the substrate. Furthermore, the HcJ did not improve sufficiently.

[0164] Regarding sample No. 4, RTB-type permanent magnets for samples No. 90 to 97 were fabricated under essentially the same conditions, except that the conditions for the first aging treatment were changed.

[0165] SEM images were obtained for the acquired RTB-type permanent magnets, as with the other samples. A 20 μm × 15 μm area was arbitrarily selected within the field of view of the SEM image and used as the observation target. The observed portion of the SEM image was binarized using image processing software. From the binarized image, the total area ratio of the low-melting point grain boundary phase and the average equivalent circle diameter of the low-melting point grain boundary phase were calculated.

[0166] Table 10 shows the oxygen, carbon, and nitrogen content, first aging treatment conditions, various parameters related to microstructure, and magnetic properties for each sample. Except for the first aging treatment conditions, the same conditions as for sample No. 4 were used.

[0167] [Table 10]

[0168] Table 10 shows that in each example, where all compositions were within a specific range, a sufficient number of two-particle grain boundary interfaces were observed before grain boundary diffusion. Furthermore, each example obtained good magnetic properties.

[0169] Figure 7 is the image obtained by binarizing the SEM image in Figure 2 (SEM image of sample No. 4 substrate at a magnification of 2500x). Figure 8 is the image obtained by binarizing the SEM image in Figure 4 (SEM image of sample No. 63 substrate at a magnification of 2500x). From Figures 7 and 8, it can be seen that the magnets of samples No. 4 and 63, which underwent the predetermined first aging treatment, have a good dispersion state of grain boundary triple points.

[0170] As shown in Table 10, RTB-type permanent magnets of samples No. 91, 4, 92, and 94-96, in which the average equivalent circle diameter of the low-melting-point grain boundary phase was 0.40 μm or more and 1.00 μm or less, or the area fraction of the low-melting-point grain boundary phase was 1.5% or more and 7.5% or less, were able to improve HcJ while maintaining a high Br.

[0171] Furthermore, RTB-type permanent magnets of samples No. 91, 4, 92, and 95-96, in which the average equivalent circle diameter of the low-melting-point grain boundary phase was 0.40 μm to 1.00 μm and the total area ratio of the low-melting-point grain boundary phase was 1.5% to 7.5%, were particularly able to improve HcJ while maintaining a high Br.

[0172] Furthermore, the magnet of sample No. 63, which underwent the first aging treatment under the same conditions as sample No. 4, also had an average equivalent circle diameter of the low-melting-point grain boundary phase of 0.40 μm to 1.00 μm, and a total area ratio of the low-melting-point grain boundary phase of 1.5% to 7.5%, demonstrating that it was possible to improve HcJ while maintaining a particularly high Br content. [Explanation of Symbols]

[0173] 1...RTB permanent magnet

Claims

1. It contains at least rare earth elements, Fe, Zr, Cu, B, C, O and N, The content of rare earth elements is 28.50% by mass or more and 32.00% by mass or less. Zr content is 0.01% by mass or more and 0.50% by mass or less. Cu content is 0.04% by mass or more and 0.50% by mass or less. Al content is 0% by mass or more and 0.60% by mass or less. The Ga content is 0% by mass or more and 0.80% by mass or less. Co content is 0% by mass or more and 3.50% by mass or less. The content of B is 0.88% by mass or more and 1.00% by mass or less. The C content is 0.05% by mass or more and 0.12% by mass or less. The O content is 0.11% by mass or more and 0.30% by mass or less, The N content is 0.015% by mass or more and 0.07% by mass or less. Fe is the actual remainder, An R-T-B type permanent magnet containing heavy rare earth elements as rare earth elements, with a heavy rare earth element content of 0.03% by mass or more and 0.20% by mass or less.

2. The R-T-B permanent magnet according to claim 1, wherein the residual magnetic flux density Br is 1400 mT or more, and the coercivity HcJ is 1900 kA / m or more.

3. The R-T-B permanent magnet according to claim 1 or 2, wherein the R-T-B permanent magnet comprises a main phase and a grain boundary triple point surrounded by three or more main phases, the grain boundary triple point is composed of a rare earth oxide phase and a low melting point grain boundary phase, and the average equivalent circle diameter of the low melting point grain boundary phase is 0.40 μm or more and 1.00 μm or less.

4. The R-T-B permanent magnet according to claim 3, wherein the total area ratio of the low-melting-point grain boundary phase is 1.5% or more and 7.5% or less.

5. The process of crushing the alloy to obtain alloy powder, The process of obtaining a molded body by compression molding the aforementioned alloy powder, The process of firing the molded body to obtain a sintered body, The process involves contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, A method for manufacturing an R-T-B permanent magnet, comprising: A method for manufacturing an R-T-B type permanent magnet, in which the amount of oxygen in the alloy powder is controlled before compression molding of the alloy powder.

6. A method for producing an R-T-B permanent magnet according to claim 5, wherein the alloy is coarsely ground by hydrogen storage pulverization to obtain a coarse powder, and the coarse powder is finely ground to obtain the alloy powder.

7. A method for producing an R-T-B permanent magnet according to claim 6, wherein the coarse powder is finely ground using a jet mill.

8. A method for manufacturing an R-T-B permanent magnet according to claim 6 or 7, wherein the coarse powder is heat-treated to control the amount of oxygen in the alloy powder by maintaining an oxygen concentration of 0.5% or more and 23% or less in the atmosphere.

9. A method for manufacturing an R-T-B permanent magnet according to claim 7, wherein the oxygen concentration in the atmosphere inside the jet mill is 0.01% or more and 0.30% or less when the fine grinding is performed, and the amount of oxygen in the alloy powder is controlled.

10. The method for manufacturing an R-T-B permanent magnet according to claim 7, wherein the internal atmosphere of the jet mill is a mixed gas atmosphere of noble gas and oxygen gas, and the amount of oxygen in the alloy powder is controlled.

11. A method for manufacturing an R-T-B permanent magnet according to claim 7, wherein the coarse powder is heat-treated with an oxygen concentration of 0.5% or more and 23% or less in the atmosphere, and the fine grinding is performed with the atmosphere inside the jet mill being a mixed gas of a noble gas and oxygen gas, or a noble gas, thereby controlling the amount of oxygen in the alloy powder.

12. A method for manufacturing an R-T-B permanent magnet according to claim 5, comprising the step of performing a first aging treatment on the sintered body before the step of heat-treating the sintered body by contacting it with a diffusion material containing a heavy rare earth element, and / or after the step of heat-treating the sintered body by contacting it with a diffusion material containing a heavy rare earth element.

13. A method for manufacturing an R-T-B permanent magnet according to claim 12, further comprising the step of performing the primary effect treatment before the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment.

14. A method for manufacturing an R-T-B permanent magnet according to claim 12 or 13, wherein the aging temperature of the primary aging treatment is 850°C or higher and 950°C or lower, and the aging time of the primary aging treatment is 1.5 hours or higher and 10 hours or lower.

15. Furthermore, the method for manufacturing an R-T-B permanent magnet according to claim 12 or 13, further comprising the step of performing a second aging treatment on the sintered body after the step of performing the first aging treatment.

16. A method for manufacturing an R-T-B permanent magnet according to claim 15, further comprising the step of heat-treating the sintered body by contacting it with a diffusion material containing heavy rare earth elements, followed by the step of performing the second aging treatment step.

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