Rare earth magnet ang method for manufacturing the same

Abstract

To provide an R-T-B-based rare earth magnet achieving both residual magnetization and coercive force.SOLUTION: The present invention relates to an R-T-B-based rare earth magnet in which R is a rare earth element, T is Fe and / or Co, and B is boron. R includes Nd. The R-T-B-based rare earth magnet includes a main phase having an R2T14B-type crystal structure and a grain boundary phase present around the main phase. The average grain size of the main phase is 0.1-1.0 μm. The main phase has a core portion and a shell portion present around the core portion. The ratio (concentration of Nd in shell portion / concentration of Nd in core portion) of the concentration of Nd (atom%) in the shell portion and in the core portion of the main phase is 1.654-1.714.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to rare earth magnets and a method for manufacturing the same.

Background Art

[0002] In recent years, as high-performance rare earth magnets, Sm-Co based rare earth magnets, R-T-B based permanent magnets, such as Nd-Fe-B based rare earth magnets, have been put into practical use.

[0003] For example, Patent Document 1 discloses an arrangement step of arranging a magnetic material, which is a molded body or a sintered body of powder particles made of a rare earth magnet alloy, and a diffusion material containing a diffusion element for improving the coercive force in proximity to each other, and a diffusion step of exposing the heated magnetic material to the vapor of the diffusion element evaporated from the heated diffusion material to diffuse the diffusion element into the magnetic material. The diffusion step is characterized in that the diffusion material is heated to a diffusion material temperature (Td) different from the magnetic material temperature (Tm), which is the heating temperature of the magnetic material, independently of the magnetic material. A method for manufacturing a rare earth magnet is disclosed.

[0004] Patent Document 2 discloses (R1 1-x R2 x ) a TM b B c M d(R1 is one or more rare earth elements including Y, R2 is a rare earth element different from R1, TM is a transition metal containing at least one of Fe, Ni, and Co, B is boron, M is at least one of Ti, Ga, Zn, Si, Al, Nb, Zr, Ni, Co, Mn, V, W, Ta, Ge, Cu, Cr, Hf, Mo, P, C, Mg, Hg, Ag, and Au, 0.01 ≦ x ≦ 1, 12 ≦ a ≦ 20, b = 100 - a - c - d, 5 ≦ c ≦ 20, 0 ≦ d ≦ 3, all in at%), a first step of manufacturing a sintered body having a structure composed of a main phase and a grain boundary phase, a second step of subjecting the sintered body to hot plastic working to manufacture a rare earth magnet precursor, and a third step of diffusing and infiltrating a melt of an R3 - M modified alloy (R3 is a rare earth element including R1 and R2) into the grain boundary phase of the rare earth magnet precursor to manufacture a rare earth magnet. A method for manufacturing a rare earth magnet is disclosed.)

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Diffusion infiltration (penetration treatment) by grain boundary diffusion is useful for improving coercivity, but the residual magnetization decreases. In order to suppress the decrease in residual magnetization due to grain boundary diffusion, when the penetration treatment temperature (thermal input) is increased to improve the Nd concentration in the main phase, there is a problem that the main phase coarsens and the coercivity decreases.)

[0007] Therefore, an object of the present invention is to provide an R - T - B - type rare earth magnet that achieves both high residual magnetization and high coercivity.)

Means for Solving the Problems

[0008] As a result of various studies on means for solving the above problems, the inventors have found that in an NdFeB-based rare earth magnet, by performing heat treatment (flash annealing) at a high temperature and for a short time after infiltration treatment at a constant temperature, it is possible to suppress a decrease in coercivity due to coarsening of the main phase, and to concentrate neodymium (Nd) in the shell portion of the main phase. As a result, it has been found that the residual magnetization and coercivity of the NdFeB-based rare earth magnet can be made compatible, and the present invention has been completed.

[0009] That is, the gist of the present invention is as follows. (1) An R-T-B-based rare earth magnet in which R is a rare earth element, T is Fe and / or Co, and B is boron, wherein R contains Nd, and the R-T-B-based rare earth magnet has an R2T 14 main phase having a B-type crystal structure and a grain boundary phase existing around the main phase, the average particle size of the main phase being 0.1 μm to 1.0 μm, the main phase having a core portion and a shell portion existing around the core portion, and the ratio of the Nd concentration (atomic% (at%)) of the shell portion to the core portion of the main phase (Nd concentration of the shell portion / Nd concentration of the core portion) being 1.654 to 1.714, the R-T-B-based rare earth magnet. (2) In X-ray diffraction analysis, when the 2θ value of the (006) plane peak of the core portion is θ1 and the 2θ value of the (006) plane peak of the main phase having a core-shell structure is θ2, 0.000 < |θ2 - θ1| ≦ 0.061, the R-T-B-based rare earth magnet according to (1). (3) In X-ray diffraction analysis, when the 2θ value of the (006) plane peak of the core portion is θ1 and the 2θ value of the (006) plane peak of the main phase having a core-shell structure is θ2, 0.030 ≦ |θ2 - θ1| ≦ 0.061, the R-T-B-based rare earth magnet according to (1) or (2). (4) A method for manufacturing the R-T-B-based rare earth magnet according to any one of (1) to (3), the method including infiltration treatment using an infiltration material containing Nd and flash annealing after the infiltration treatment, and the temperature of the infiltration treatment being T GBD (°C), and the temperature of the flash annealing being T FA (°C), when 600 (°C) ≦ T GBD≤700 (°C) and 0.340 T GBD +473 (°C) ≤ T FA ≤0.248 T GBD The method satisfying +636 (°C).

Advantages of the Invention

[0010] According to the present invention, an R-T-B rare earth magnet achieving both residual magnetization and coercive force is provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the rare earth magnet and its manufacturing method of the present invention are not limited to the following embodiments, and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art without departing from the gist of the present invention.

[0013] In the R-T-B-based rare earth magnet of the present invention, R is a rare earth element, R includes neodymium, and in addition to neodymium, for example, it may include one or more selected from the group consisting of cerium, lanthanum, yttrium, scandium, praseodymium, gadolinium, terbium, dysprosium, and holmium. In one embodiment, R is neodymium, cerium, and lanthanum. Also, T is an iron group element, which is iron, cobalt, or iron and cobalt (iron and / or cobalt), and here, the ratio of each element in the case of iron and cobalt is not limited. In one embodiment, T is iron. Further, B is boron. Note that the R-T-B-based rare earth magnet of the present invention may include one or more selected from the group consisting of additive elements known in the art, such as titanium, vanadium, copper, chromium, manganese, nickel, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, aluminum, gallium, silicon, bismuth, tin, and carbon, as long as the coercivity of the R-T-B-based rare earth magnet is not impaired.

[0014] In the R-T-B rare earth magnet of the present invention, the content of R is usually 12.8 atomic % to 14.5 atomic % with respect to the total number of atoms of the R-T-B rare earth magnet. In one embodiment, for R, with respect to the total number of atoms of the R-T-B rare earth magnet, the content of Nd is usually 6.2 atomic % to 6.4 atomic %, the content of Ce is usually 3.2 atomic % to 3.4 atomic %, and the content of La is usually 3.2 atomic % to 3.4 atomic %. In the R-T-B rare earth magnet of the present invention, the content of T is usually 79.4 atomic % to 81.6 atomic % with respect to the total number of atoms of the R-T-B rare earth magnet. In one embodiment, for T, with respect to the total number of atoms of the R-T-B rare earth magnet, the content of Fe is usually 80.4 atomic % to 81.4 atomic %, and the content of Co is usually 0.0 atomic % to 1.0 atomic %. In the R-T-B rare earth magnet of the present invention, the content of B is usually 5.3 atomic % to 6.1 atomic % with respect to the total number of atoms of the R-T-B rare earth magnet. In the R-T-B rare earth magnet of the present invention, the content of the additive element is usually 0.30 atomic % to 1.1 atomic % with respect to the total number of atoms of the R-T-B rare earth magnet. In one embodiment, for the additive element, with respect to the total number of atoms of the R-T-B rare earth magnet, the content of Ga is usually 0.30 atomic % to 0.45 atomic %, the content of Cu is usually 0.10 atomic % to 0.15 atomic %, and the content of Al is usually 0.05 atomic % to 0.30 atomic %. Note that the content of each element in the R-T-B rare earth magnet may be calculated based on the addition amount of each element during manufacturing, but it can be measured by methods known in the art, such as X-ray fluorescence analysis (XRF), inductively coupled plasma mass spectrometry (ICP-MS), etc.

[0015] By the R-T-B rare earth magnet being composed of the above elements, it can have high residual magnetization and high coercive force.

[0016] The R-T-B rare earth magnet of the present invention has a main phase with an R2T 14 B-type crystal structure and a grain boundary phase existing around the main phase. The R2T constituting the main phase 14Crystals having a B-type crystal structure are bonded to each other through a grain boundary phase. In other words, the main phase is segmented by the grain boundary phase, and thus magnetically segmented as well, which can suppress magnetization reversal and have a higher coercivity compared to the case where it is not segmented by the grain boundary phase.

[0017] The average particle size of the main phase is from 0.1 μm to 1.0 μm, and in one embodiment, it is from 0.1 μm to 0.6 μm.

[0018] Here, the "average particle size" is measured as follows. In a scanning electron microscope image or a transmission electron microscope image, a certain area is defined by observing from the direction perpendicular to the easy magnetization axis, and a plurality of lines are drawn in the direction perpendicular to the easy magnetization axis for the main phase existing within this certain area. The diameter (length) of the main phase is calculated from the distance between the points where the lines intersect within the particles of the main phase (sectioning method). When the cross-section of the main phase is close to a circle, it is converted to the equivalent diameter of the projected area circle. When the cross-section of the main phase is close to a rectangle, it is converted by rectangular parallelepiped approximation. The value of D50 of the distribution (particle size distribution) of the diameter (length) obtained in this way is the average particle size.

[0019] When the average particle size of the main phase is within the above range, the coercivity of the rare earth magnet can be improved.

[0020] The main phase has a core part and a shell part existing around the core part.

[0021] The average particle size of the core part of the main phase is usually 900 nm or less. The average thickness of the shell part of the main phase is usually 50 nm or less, and in one embodiment, it is from 1 nm to 30 nm. Note that the particle size of the core part corresponds to the value obtained by subtracting 2×(the thickness of the shell part) from the particle size of the main phase.

[0022] Here, the average thickness of the shell part of the main phase can be measured as the composition modulation part from the core part by TEM-EDX analysis or the like.

[0023] In the main phase, regarding the Nd concentration in the shell part, the standard of the shell part is not limited. For example, the Nd concentration in the shell part indicates the number of Nd atoms (atomic %) relative to the total number of atoms of rare earth elements in the shell part. Regarding the Nd concentration in the core part, the standard of the core part is the same as the standard of the Nd concentration in the shell part. For example, when the standard of the Nd concentration in the shell part is the total number of atoms of rare earth elements in the shell part as described above, the Nd concentration in the core part indicates the number of Nd atoms (atomic %) relative to the total number of atoms of rare earth elements in the core part. The Nd concentration in the shell part is higher than the Nd concentration in the core part, and the ratio of the Nd concentrations (atomic %) of the shell part and the core part (Nd concentration in the shell part / Nd concentration in the core part) is 1.654 to 1.714. The Nd concentration in the shell part is not limited as long as it has the relationship with the Nd concentration in the core part as described above, but it is usually 80 atomic % to 85 atomic % relative to the total number of atoms of rare earth elements in the shell part. Note that the Nd concentration of each part can be obtained from the relationship between the EDX analysis and the difference Δ2θ between the (006) plane peaks of the core part and the shell part described below and the Nd concentration measured by the EDX analysis.

[0024] In the X-ray diffraction (XRD) analysis of the main phase, when the 2θ value of the (006) plane peak of the core part or the 2θ value of the (006) plane peak of the main phase of the rare earth magnet precursor before the infiltration treatment with no composition change is θ1, and after the infiltration treatment, that is, the 2θ value of the (006) plane peak of the main phase of the rare earth magnet is θ2, the absolute value of Δ2θ, |θ2 - θ1|, is usually more than 0.000 to 0.061, and in one embodiment, it is 0.030 to 0.061.

[0025] The reason why the 2θ values of the (006) plane peaks of the main phase of the rare earth magnet precursor having only the core part before the infiltration treatment with no compositional change and the main phase of the rare earth magnet having a core-shell structure after the infiltration treatment are different is that there is a difference in the Nd concentration between the core part and the shell part in the rare earth magnet of the present invention. That is, in the shell part, rare earth elements other than Nd in the core part, such as Ce and / or La, have replaced Nd. Therefore, a shift occurs in the crystal lattice sizes of the core and the shell based on the sizes of the respective elements. As a result, the difference appears in the 2θ value of the (006) plane peak. For example, when a rare earth element (La) larger than Nd in the core part replaces Nd in the shell part, the shell part shrinks more than the core part. As a result, (θ2 - θ1) can be positive. On the other hand, for example, when a rare earth element (Ce) smaller than Nd in the core part replaces Nd in the shell part, the shell part expands more than the core part. As a result, (θ2 - θ1) can be negative.

[0026] Rather than increasing the residual magnetization and coercive force in the core part, increasing the residual magnetization and coercive force in the shell part can more efficiently use rare earth elements to increase the residual magnetization and coercive force. The residual magnetization and coercive force increase as the content ratio of neodymium increases. Therefore, by the infiltration treatment of the infiltrant, rare earths such as cerium in the rare earth magnet precursor, for example, cerium, lanthanum, gadolinium, yttrium, and scandium are discharged from the shell part to the grain boundary phase, and the neodymium in the infiltrant is infiltrated from the grain boundary phase into the shell part, which is advantageous for improving the residual magnetization and coercive force.

[0027] The R-T-B-based rare earth magnet of the present invention is usually processed into an arbitrary shape for use. The shape of the R-T-B-based rare earth magnet of the present invention is not particularly limited. The shape of the R-T-B-based rare earth magnet of the present invention can take any shape, for example, a rectangular parallelepiped, a hexahedron, a flat plate shape, a columnar shape such as a quadrangular prism, a cylindrical shape with a C-shaped cross-section of the R-T-B-based rare earth magnet, etc.

[0028] In addition, the R-T-B-based rare earth magnet of the present invention includes both a magnet product magnetized after processing the magnet and a magnet product not magnetized.

[0029] Since the R-T-B-based rare earth magnet of the present invention has the above-described configuration and composition, the R-T-B-based rare earth magnet of the present invention can have a high residual magnetization Br, for example, usually a residual magnetization Br of 1.17 T to 1.20 T, and a high coercive force Hc, for example, usually a coercive force Hc of 900 kA / m to 1150 kA / m.

[0030] The R-T-B-based rare earth magnet of the present invention can be manufactured using known techniques in the art, except that a rare earth magnet precursor and an infiltration material are prepared so as to have the configuration and composition of the R-T-B-based rare earth magnet of the present invention, and at the time of grain boundary diffusion, an infiltration material containing Nd is infiltrated at a certain temperature, and further, flash annealing is performed at a certain temperature after the infiltration treatment.

[0031] The R-T-B-based rare earth magnet of the present invention can be manufactured, for example, as follows. First, a rare earth magnet precursor is prepared by melt preparation, melt cooling, sintering, and optionally anisotropy imparting, which will be described below. (Melt preparation) Prepare a melt adjusted to the composition of the R-T-B-based rare earth magnet of the present invention. For elements that may be depleted in subsequent processes, the depletion may be taken into account.

[0032] (Melt cooling) Subsequently, the melt having the above-described composition is supercooled rapidly. "Supercooled rapidly" means cooling usually at 5×10 5 °C / second or more, in one embodiment 1×10 6 °C / second or more, and usually 5×10 7 °C / second or less, in one embodiment 1×10 7 °C / second or less. When the melt having the above-described composition is supercooled rapidly, a magnetic thin strip or magnetic thin sheet having a nanocrystallized main phase can be obtained.

[0033] As the ultra-rapid cooling method, it is not limited as long as the molten metal can be ultra-rapidly cooled at the above-described speed. As the ultra-rapid cooling method, typically, the liquid quenching method can be applied. Alternatively, the cooling roll of the strip casting method may be rotated at a high speed to perform ultra-rapid cooling. For the liquid quenching method, refer to, for example, JP-A-2022-68679 and JP-A-2023-136838.

[0034] (Sintering) Furthermore, the magnetic thin strip or magnetic thin sheet is sintered to obtain a sintered body (rare earth magnet precursor). As the sintering method and conditions, well-known ones can be applied. As sintering, pressure sintering is used. In pressure sintering, compared with the generally known non-pressure sintering, by applying a pressure, the magnetic thin strip or magnetic thin sheet can be sintered at a relatively low temperature and in a short time. Therefore, pressure sintering is typically applied to the sintering of a magnetic thin strip or magnetic thin sheet having a nanocrystallized main phase. Thereby, a sintered body can be obtained without coarsening the nanocrystallized main phase.

[0035] The conditions during sintering can be appropriately determined so that the main phase does not coarsen and a good sintered body density can be obtained. The conditions during sintering in pressure sintering will be described below.

[0036] The hot-pressing sintering temperature is, for example, usually 470°C or higher, and in one embodiment, 500°C or higher, and usually 750°C or lower, and in one embodiment, 700°C or lower. The hot-pressing sintering pressure is, for example, usually 50 MPa or higher, and in one embodiment, 100 MPa or higher, and usually 600 MPa or lower, and in one embodiment, 500 MPa or lower. The hot-pressing sintering time is, for example, usually 0.5 minutes or longer, and in one embodiment, 1 minute or longer, and usually 150 minutes or shorter, and in one embodiment, 120 minutes or shorter. After the completion of hot-pressing sintering, after taking out the sintered body from the sintering mold, it is preferable to rapidly cool the sintered body. Thereby, the generation of phases other than the desired phase can be suppressed. The cooling rate is, for example, usually 10°C / min or higher, and in one embodiment, 30°C / min or higher, and usually 1000°C / min or lower, and in one embodiment, 800°C / min or lower. In order to suppress the oxidation of the magnetic thin strip or magnetic thin sheet during hot-pressing sintering, an inert gas atmosphere is preferable for the hot-pressing sintering atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0037] (Anisotropy imparting) In addition, an anisotropy imparting step can optionally be provided to the obtained rare earth magnet precursor for improving the residual magnetization. Well-known methods can be applied for anisotropy imparting. When the main phase is nanocrystallized, it is typical to perform hot plastic working on the sintered body. Hereinafter, hot plastic working will be described.

[0038] (Hot plastic working) The sintered body obtained by hot-pressing sintering is subjected to hot plastic working. Thereby, anisotropy can be imparted to the rare earth magnet of the present disclosure. The conditions of hot plastic working may be appropriately determined so as to impart anisotropy to the sintered body while avoiding coarsening of the main phase.

[0039] The hot plastic working temperature is, for example, usually 690°C or higher, and in one embodiment, 700°C or higher, and usually 850°C or lower, and in one embodiment, 840°C or lower. The hot plastic working time is, for example, usually 1 second or longer, and in one embodiment, 3 seconds or longer, and usually 10 minutes or shorter, and in one embodiment, 5 minutes or shorter. Further, the hot plastic working pressure is, for example, usually 50 MPa or higher, and in one embodiment, 100 MPa, and usually 3000 MPa or lower, and in one embodiment, 2500 MPa or lower. The reduction ratio is, for example, usually 10% or higher, and in one embodiment, 30% or higher, and usually 80% or lower, and in one embodiment, 75% or lower. The strain rate during hot plastic working is, for example, usually 0.01 / s or higher, and in one embodiment, 0.1 / s or higher, and usually 15.0 / s or lower, and in one embodiment, 10.0 / s or lower.

[0040] After completion of the hot plastic working, it is preferable to rapidly cool the sintered body. Thereby, coarsening of the main phase can be avoided, and generation of a harmful phase that adversely affects magnetism can be suppressed. The cooling rate is, for example, usually 10°C / min or higher, and in one embodiment, 30°C / min or higher, and usually 1000°C / min or lower, and in one embodiment, 800°C / min or lower. In order to suppress oxidation of the sintered body during hot plastic working, the hot plastic working atmosphere is preferably an inert gas atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0041] Subsequently, as described below, an impregnating material is impregnated into the obtained rare earth magnet precursor. (Impregnation treatment) An impregnating material is impregnated into the rare earth magnet precursor obtained by pressure sintering and optionally imparting anisotropy. Thereby, the coercivity of the rare earth magnet of the present invention, particularly the coercivity at high temperature, can be advantageously improved.

[0042] The infiltration treatment of the infiltrant is to prepare the infiltrant and infiltrate the infiltrant into the rare earth magnet precursor. The infiltrant is also called a diffusion material. The infiltrant contains 60 atomic % to 90 atomic % of neodymium, and in one embodiment, 70 atomic % to 80 atomic %, based on the total constituent elements of the infiltrant. The infiltrant may further contain one or more elements selected from the group consisting of praseodymium, terbium, dysprosium, holmium, and copper. In one embodiment, the infiltrant is an alloy composed of neodymium and copper.

[0043] As a method for preparing the infiltrant, for example, there is a method of obtaining a ribbon and / or a thin sheet from a molten metal having the composition of the infiltrant using a liquid quenching method or a strip casting method. In these methods, since the molten metal is super rapidly quenched or rapidly quenched, there is little segregation in the infiltrant, which is preferable. As other methods for preparing the infiltrant, for example, there is a method of casting a molten metal having the composition of the infiltrant into a mold such as a book mold. In this method, a large amount of infiltrant can be obtained relatively easily. In order to reduce the segregation of the infiltrant, the book mold is preferably made of a material having a high thermal conductivity. Further, it is preferable to perform a homogenization heat treatment on the casting material to suppress segregation. Furthermore, as a method for preparing the infiltrant, there is a method of charging the raw material of the infiltrant into a container, arc melting the raw material in the container, and cooling the melt to obtain an ingot. In this method, even when the melting point of the raw material is high, the infiltrant can be obtained relatively easily. From the viewpoint of reducing the segregation of the infiltrant, it is preferable to perform a homogenization heat treatment on the ingot.

[0044] As a method for the infiltration treatment, typically, the infiltrant is brought into contact with the rare earth magnet precursor to obtain a contact body, and the contact body is heated so that the melt of the infiltrant diffuses and infiltrates into the interior of the rare earth magnet precursor. The melt of the infiltrant diffuses and infiltrates through the grain boundary phase. Then, the melt of the infiltrant solidifies in the grain boundary phase, magnetically disconnects the main phases from each other, and advantageously improves the coercive force, particularly the coercive force at high temperatures.

[0045] The mode of the contact body is not particularly limited as long as the infiltrant contacts the rare earth magnet precursor. Examples of the mode of the contact body include a mode in which a ribbon and / or a flake infiltrant obtained by a liquid quenching method and / or a strip casting method is brought into contact with the rare earth magnet precursor. Further, examples of the mode of the contact body include a mode in which an infiltrant powder obtained by pulverizing a ribbon and / or a flake, a book mold material, or an arc melting and solidifying material obtained by a liquid quenching method and / or a strip casting method is brought into contact with the rare earth magnet precursor.

[0046] The infiltration treatment conditions are conditions under which the infiltrant diffuses and penetrates into the interior of the rare earth magnet precursor, the main phase does not coarsen, and the generation of harmful phases that adversely affect magnetism can be suppressed.

[0047] The infiltration treatment temperature (T GBD ) is 600 °C or higher and 700 °C or lower. The infiltration treatment time is usually 5 minutes or longer, in one embodiment 30 minutes or longer, and usually 300 minutes or shorter, in one embodiment 180 minutes or shorter. After the infiltration treatment of the infiltrant, the sintered body is rapidly cooled. Thereby, the generation of harmful phases that adversely affect magnetism can be suppressed. The cooling rate is, for example, usually 10 °C / min or higher, in one embodiment 30 °C / min or higher, and usually 1000 °C / min or lower, in one embodiment 800 °C / min or lower. In order to suppress the oxidation of the rare earth magnet precursor during the infiltration treatment, the infiltration treatment atmosphere may be an inert gas atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0048] When the infiltrant diffuses and penetrates, the amount of the infiltrant brought into contact with the rare earth magnet precursor is not limited as long as the (Nd concentration in the shell part / Nd concentration in the core part) as described above is obtained. The amount of the infiltrant is, for example, usually 1.0 wt% to 10.0 wt% based on the total weight of the rare earth magnet precursor.

[0049] In order to diffuse and penetrate the infiltrant under the condition that the main phase of the rare earth magnet precursor does not coarsen, the average particle size of the main phase before the infiltration treatment of the infiltrant and the average particle size of the main phase after the infiltration treatment of the infiltrant are substantially in the same range. The average particle size and crystal structure of the main phase are as described above.

[0050] Also, the infiltration treatment usually changes the composition of the grain boundary phase and the shell part of the main phase. In other words, the part where the composition changes due to the infiltration treatment in the main phase corresponds to the shell part in the main phase. Therefore, the composition of the core part in the main phase of the rare earth magnet precursor is substantially the same before and after the infiltration treatment.

[0051] By the infiltration treatment of the rare earth magnet precursor, Nd infiltrates into the shell part in the main phase, so that the Nd concentration in the shell part becomes higher than that in the core part, and high residual magnetization and high coercive force of the obtained rare earth magnet can be realized.

[0052] Subsequently, a rare earth magnet is manufactured by flash annealing the rare earth magnet precursor after the infiltration treatment, which will be described below.

[0053] (Flash Annealing) "Flash annealing" means heat treatment at a high temperature for a short time.

[0054] Flash annealing can be carried out by a heating device whose heating method is an infrared condensing method, although it is not limited.

[0055] The heating rate in flash annealing is, for example, usually 600 °C / min or more, in one embodiment 800 °C / min or more, in one embodiment 900 °C / min or more, and usually 60000 °C / min or less, in one embodiment 1200 °C / min or less. The flash annealing temperature (T FA ) is, when the temperature of the infiltration treatment is T GBD (°C), (0.340T GBD + 473) °C or more (0.248T GBDThe temperature is in the range below +636)°C. The flash annealing temperature is not limited as long as it is within the above range, but is usually 600°C or higher, and in one embodiment 680°C or higher, and usually 900°C or lower, and in one embodiment 810°C or lower. The flash annealing time is, for example, usually 0 seconds or more and usually 0.5 seconds or less. Note that the "flash annealing temperature" is the temperature reached at the surface of the rare earth magnet precursor, and the "flash annealing time" is the time during which the rare earth magnet precursor is held at the reached temperature after reaching the reached temperature. Therefore, "a flash annealing time of 0 seconds" means that the rare earth magnet precursor is immediately cooled without a holding time after reaching the flash annealing temperature.

[0056] After the flash annealing is completed, the rare earth magnet is rapidly cooled. Thereby, coarsening of the main phase can be avoided, and generation of a harmful phase that adversely affects magnetism can be suppressed. The cooling rate is, for example, usually 10°C / min or more, and in one embodiment 30°C / min or more, and usually 1000°C / min or less, and in one embodiment 800°C / min or less. In order to suppress oxidation of the rare earth magnet during flash annealing, an inert gas atmosphere is preferably used as the flash annealing atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0057] Regarding the rare earth magnet after infiltration treatment and flash annealing, as defined above, in the X-ray diffraction (XRD) analysis of the main phase, θ1 is the (006) plane peak of the main phase of the rare earth magnet precursor before infiltration treatment, which reflects the (006) plane peak of the core part, and θ2 is the (006) plane peak of the main phase of the rare earth magnet after infiltration treatment and flash annealing, which reflects the (006) plane peak of the shell part. The absolute value of Δ2θ, |θ2 - θ1|, is usually more than 0.000 to 0.061, and in one embodiment, it is 0.030 to 0.061. Here, in principle, since there is no composition change in the core part before and after infiltration treatment, the (006) plane peak of the main phase of the rare earth magnet precursor before infiltration treatment reflects the (006) plane peak of the core part before infiltration treatment and the (006) plane peak of the core part after infiltration treatment and flash annealing. Regarding the shell part, since there is a composition change before and after infiltration treatment, the (006) plane peak of the main phase of the rare earth magnet after infiltration treatment and flash annealing reflects the superposition of the (006) plane peak of the core part and the (006) plane peak of the shell part.

[0058] By flash annealing the rare earth magnet precursor, while avoiding coarsening of the main phase, Nd is concentrated in the shell part of the main phase, the Nd concentration in the shell part becomes higher than that in the core part, and high residual magnetization and high coercive force of the obtained rare earth magnet can be realized.

[0059] Finally, the rare earth magnet after flash annealing may be heat-treated for stabilization. (Heat treatment) Well-known methods and conditions of heat treatment can be applied. The heat treatment is carried out to stabilize the rare earth magnet after flash annealing, and is carried out at a temperature and for a time within a range where the nanocrystallized main phase does not coarsen and the composition does not change.

[0060] Therefore, the conditions of the heat treatment can be appropriately determined so that the main phase does not coarsen and is stabilized. The conditions of the heat treatment will be described below.

[0061] The heat treatment temperature is, for example, usually 350°C or higher, and in one embodiment, 400°C or higher, and usually 700°C or lower, and in one embodiment, 500°C or lower. The heating rate is, for example, usually 100°C / min or higher and usually 300°C / min or lower. The heat treatment time is, for example, usually 0.5 minutes or longer, and in one embodiment, 1 minute or longer, and usually 150 minutes or shorter, and in one embodiment, 60 minutes or shorter. After the heat treatment is completed, it is preferable to quickly cool the rare earth magnet after taking it out of the heat treatment apparatus, for example, a firing furnace. Thereby, generation of phases other than the desired phase can be suppressed. The cooling rate is, for example, usually 10°C / min or higher, and in one embodiment, 30°C / min or higher, and usually 1000°C / min or lower, and in one embodiment, 800°C / min or lower. To suppress oxidation of the rare earth magnet during heat treatment, an inert gas atmosphere is preferable for the heat treatment atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

Examples

[0062] Hereinafter, several examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

[0063] Based on the description of the method for manufacturing the rare earth magnet, rare earth magnets were manufactured as follows. 1. Method for manufacturing a hot-worked magnet For the hot-worked magnet precursor made of the base material composition shown in Table 1, Nd 80 Cu 20 (atomic%) alloy was attached to both sides of the magnet as an infiltrant, and infiltration treatment was carried out. The weight of the infiltrant was 9 wt% or 10 wt% based on the total weight of the hot-worked magnet precursor, and the infiltration treatment temperature and infiltration treatment time were the conditions shown in Table 2.

[0064] Next, rapid heating (flash annealing) was performed to the target temperature shown in Table 2 at a heating rate of 600 (°C / min) or 1200 (°C / min). Thereafter, optimization heat treatment was carried out at 425°C for 60 minutes.

[0065]

Table 1

[0066]

Table 2

[0067] 2. Evaluation of Hot-Worked Magnets After evaluating the magnetic properties of the obtained hot-worked magnets using a VSM (Vibrating Sample Magnetometer Model 8607, manufactured by Lake Shore), X-ray diffraction analysis (a fully automatic multi-purpose X-ray diffractometer SmartLab, manufactured by Rigaku Corporation) was performed to measure the value of Δ2θ of the (006) plane peak of the NdFeB crystal structure. In addition, the concentration (atomic %) of each component in the shell part was measured by STEM-EDX analysis (Talos F200X, manufactured by FEI).

[0068] 3. Evaluation Results of Hot-Worked Magnets Figure 1A shows the X-ray diffraction (XRD) spectra of the hot-worked magnet of Comparative Example 11 before (black) and after (gray) infiltration treatment. From Figure 1A, it was found that as the Nd concentration in the shell part improves, the NdFeB crystal lattice contracts, and this change appears as a peak shift to the high-angle side of the (006) plane in the XRD spectrum. Figure 1B shows the relationship between the peak shift amount (Δ2θ) to the high-angle side of the (006) plane of the NdFeB crystal measured by X-ray diffraction analysis and the Nd concentration in the shell part measured by STEM-EDX analysis for Comparative Example 11 and Example 22. Although Comparative Example 11 and Example 22 are used in Figure 1B, in the comparative examples and examples, the magnet base materials used are the same, and after heat treatment, all form the same NdFeB-based rare earth magnet structure (without transformation). Therefore, from the relationship in Figure 1B, the Nd concentration in the shell part of each prepared sample was quantitatively evaluated. The Nd concentration in the shell part indicates the number of Nd atoms (atomic %) relative to the total number of atoms of rare earth elements in the shell part.

[0069] Table 3 shows the obtained data (magnetic property evaluation results and tissue analysis results).

[0070]

Table 3

[0071] 2 and 3 show the residual magnetization (FIG. 2) and coercivity (FIG. 3) versus the ratio of the Nd concentration in the shell part to the Nd concentration in the core part (Nd concentration in the shell part / Nd concentration in the core part) of the hot-processed magnets of the examples and comparative examples. From FIGS. 2 and 3, it was found that the hot-processed magnets of the examples, which were flash-annealed at an appropriate temperature, had high residual magnetization (1.17 T or more) while maintaining the same level of coercivity (900 kA / m or more) as hot-processed magnets that had been subjected to normal infiltration treatment. In addition, considering the technical common sense that there is a linear relationship between the Nd concentration in the main phase shell part and the residual magnetization, in the results of Table 3, there is also a linear relationship between Δ2θ and the residual magnetization (however, in Comparative Example 4, the relationship deviates from the linear relationship due to the disturbance in the composition of the obtained magnet caused by the high infiltration treatment temperature), so the reliability of the calibration curve in FIG. 1B, which shows a linear relationship between Δ2θ and the Nd concentration, can be confirmed.

[0072] FIG. 4 shows the infiltration treatment temperature T GBD and flash annealing temperature T FA From Figure 4, T GBD and T FA However, 600(℃)≦T GBD ≦700(℃) and (0.340T GBD +473)(℃)≦T FA ≦(0.248T GBD +636) (℃), a higher remanence can be obtained than in Comparative Example 2, which was not subjected to flash annealing. This is because the Nd concentration in the shell part of the main phase increases due to flash annealing. However, if the flash annealing temperature is too high, the coercivity tends to decrease due to coarsening of the main phase.

[0073] Fig. 5 shows the results of analyzing the microstructural changes due to flash annealing by STEM-EDX. As a result of line analysis, the Nd concentration in the shell of the hot-worked magnet without flash annealing was 79.8% from Fig. 5A (Comparative Example 11), while the Nd concentration in the shell of the hot-worked magnet with flash annealing was 82.6% from Fig. 5B (Example 22).

[0074] Fig. 6 schematically shows the core-shell structure of the main phase in the hot-worked magnet subjected to flash annealing. It can be seen from Fig. 6 that the Nd concentration in the shell is higher than that in the core.

Claims

1. An R-T-B rare earth magnet wherein R is a rare earth element, T is Fe and / or Co, and B is boron, R contains Nd, the R-T-B rare earth magnet has a main phase having an R ２ T １４ B-type crystal structure, and a grain boundary phase existing around the main phase, the average particle size of the main phase is 0.1 μm to 1.0 μm, the main phase has a core part and a shell part existing around the core part, the ratio (Nd concentration in the shell part / Nd concentration in the core part) of the Nd concentration (atomic %) of the shell part to the core part of the main phase is 1.654 to 1.714, the R-T-B rare earth magnet.

2. In X-ray diffraction analysis, when the 2θ value of the (006) plane peak of the core part is θ1 and the 2θ value of the (006) plane peak of the main phase having a core-shell structure is θ2, 0.000 < |θ2 - θ1| ≦ 0.

061. The R-T-B rare earth magnet according to Claim 1.

3. In X-ray diffraction analysis, when the 2θ value of the (006) plane peak of the core part is θ1 and the 2θ value of the (006) plane peak of the main phase having a core-shell structure is θ2, 0.030 ≦ |θ2 - θ1| ≦ 0.

061. The R-T-B rare earth magnet according to Claim 1.

4. A method for manufacturing the R-T-B rare earth magnet according to Claim 1, the method includes an infiltration treatment using an infiltration material containing Nd and a flash annealing after the infiltration treatment, when the temperature of the infiltration treatment is T ＧＢＤ (°C) and the temperature of the flash annealing is T ＦＡ (°C), 600 (°C) ≦ T ＧＢＤ ≦ 700 (°C), and 0.340T ＧＢＤ + 473 (°C) ≦ T ＦＡ ≦ 0.248T ＧＢＤ + 636 (°C) is satisfied. The aforesaid method.

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