R-T-B series permanent magnet

Abstract

To provide a low-cost rare earth magnet including Ce, which is high in HcJ.SOLUTION: There is provided an R-T-B based permanent magnet including main phase particles comprising an R2T14B compound (R represents a rare earth element, T represents a transition metal element, and B represents boron), and grain boundaries. R includes Ce. A content of Ce relative to a total content of R in the R-T-B based permanent magnet is 15 mass% or more and 35 mass% or less. The grain boundaries include an R rich phase and an R-T phase. In a cross section of the R-T-B based permanent magnet, when S(R-T) represents an area ratio of the R-T phase relative to the grain boundaries, S(R-T) is 0.60 or more and 0.85 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an R-T-B-based permanent magnet.

Background Art

[0002] Patent Document 1 describes an R-T-B-based permanent magnet containing Ce as R and including an R-T phase within a predetermined range. Due to the above characteristics, an R-T-B-based permanent magnet with improved flexural strength can be obtained.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, among rare earth elements, Ce has a low cost. Therefore, it is required to obtain a rare earth magnet using Ce that has sufficient magnetic properties, particularly sufficient coercive force (HcJ).

[0005] The present invention aims to obtain a low-cost rare earth magnet containing Ce and having a high HcJ.

Means for Solving the Problems

[0006] To achieve the above object, the R-T-B-based permanent magnet according to the present invention is R 2 T 14 an R-T-B-based permanent magnet including main phase particles composed of an R-T-B compound (where R is a rare earth element, T is a transition metal element, and B is boron) and a grain boundary, R contains Ce, the content of Ce with respect to the total content of R in the R-T-B-based permanent magnet is 15% by mass or more and 35% by mass or less, The grain boundaries contain an R-rich phase and an R-T phase, In the cross-section of the R-T-B sintered magnet, with the area ratio of the R-T phase to the grain boundary being S(R-T), S(R-T) is 0.60 or more and 0.85 or less.

[0007] The content of Ga may be 0 mass% or more and 0.2 mass% or less.

[0008] It may not substantially contain La and Y.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described based on embodiments. The R-T-B permanent magnet of the present invention can be an R-T-B sintered magnet.

[0011] (Composition) The composition of the R-T-B sintered magnet will be described. R is a rare earth element. R contains cerium (Ce). By including Ce in R, the raw material cost is reduced. Further, it becomes easier to contain the R-T phase described later in the grain boundaries. Also, in order to suitably control the raw material cost of the R-T-B sintered magnet and the magnetic properties of the R-T-B sintered magnet, it is preferable to contain one or more selected from neodymium (Nd) and praseodymium (Pr) as R.

[0012] T is a transition metal element. T may be an iron group element (iron (Fe), cobalt (Co), and nickel (Ni)). T may be Fe, or a combination of Fe and Co. B is boron.

[0013] Furthermore, the R-T-B sintered magnet may contain one or more selected from metal elements other than transition metal elements. For example, it may contain one or more selected from aluminum (Al) and gallium (Ga). Furthermore, it may contain carbon (C).

[0014] Hereinafter, the content of each element in the R-T-B sintered magnet will be described.

[0015] There is no particular limitation on the content of each element in the R-T-B sintered magnet. The total content of R may be 30.00 mass% or more and 34.00 mass% or less, or may be 32.00 mass% or more and 34.00 mass% or less, with the entire R-T-B sintered magnet being 100 mass%. Note that the content of each element shown below is the content when the entire R-T-B sintered magnet is 100 mass%, unless otherwise specified.

[0016] The content of B may be 0.70 mass% or more and 0.95 mass% or less, or may be 0.80 mass% or more and 0.90 mass% or less.

[0017] The content of Co may be 0.50 mass% or more and 3.00 mass% or less, or may be 2.00 mass% or more and 3.00 mass% or less.

[0018] The R-T-B sintered magnet may or may not contain Ga. The content of Ga may be 0 mass% or more and 0.20 mass% or less, or may be 0 mass% or more and 0.10 mass% or less. The smaller the content of Ga, the smaller the S(R-T) (area ratio of the R-T phase to the grain boundary) tends to be. Also, the smaller the content of Ga, the more likely HcJ is to improve.

[0019] The R-T-B sintered magnet may or may not contain Al. The Al content may be 0.20 mass% or more and 1.00 mass% or less, or may be 0.30 mass% or more and 0.90 mass% or less.

[0020] The R-T-B sintered magnet may or may not contain copper (Cu) as T. The Cu content may be 0 mass% or more and 0.50 mass% or less, or may be 0 mass% or more and 0.25 mass% or less.

[0021] The R-T-B sintered magnet may or may not contain zirconium (Zr) as T. The Zr content may be 0.10 mass% or more and 1.00 mass% or less, or may be 0.40 mass% or more and 0.60 mass% or less.

[0022] The Ce content with respect to the total R content is 15 mass% or more and 35 mass% or less, and may be 15 mass% or more and 25 mass% or less. When the Ce content with respect to the total R content is within the above range, S(R-T) described later is likely to be 0.60 or more and 0.85 or less. As a result, HcJ and HcJ / Ha described later are likely to be high. In addition, when the Ce content with respect to the total R content is 15 mass% or more, the raw material cost is likely to be sufficiently reduced. When the Ce content with respect to the total R content is too low, the raw material cost is not sufficiently reduced. This is because the merit of being less expensive than other rare earth elements is offset by the demerit of complicating the manufacturing process by increasing the types of raw material metals containing rare earth elements.

[0023] The total content of heavy rare earth elements may be 0 mass% or more and 0.10 mass% or less. The higher the content of heavy rare earth elements, the more likely HcJ is to increase, but the cost becomes higher. Also, the higher the content of heavy rare earth elements, the more likely Br is to decrease. Heavy rare earth elements refer to Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0024] Further, it is preferable that R substantially does not contain yttrium (Y) and lanthanum (La). Substantially not containing Y and La means that the total content of Y and La in R is 0.5 mass% or less. When Y and La are substantially contained, the R-T phase described later is less likely to be formed, and it is difficult to make S(R-T) 0.60 or more. And, the effect of improving HcJ by the R-T phase is difficult to obtain. Further, when Y is contained, the anisotropy magnetic field of the main phase particles is also likely to decrease. When La is contained, the anisotropy magnetic field of the main phase particles is also likely to decrease, and the corrosion resistance is also likely to decrease.

[0025] The R-T-B sintered magnet may or may not contain C. The content of C may be 0 mass% or more and 0.3 mass% or less.

[0026] Fe may be substantially the remainder among the components of the R-T-B sintered magnet. Substantially being the remainder of Fe means that the elements contained other than the group consisting of R, B, Co, Ga, Al, Cu, Zr, and C are only Fe and inevitable impurities. And, the total content of the inevitable impurities may be 0.5 mass% or less (including 0) with respect to the R-T-B sintered magnet.

[0027] (Fine Structure) Hereinafter, the R-T-B sintered magnet 1 will be described with reference to the drawings, particularly FIG. 1. Note that FIG. 1 is a backscattered electron image obtained by observing a cross section of Example 1 described later with a field emission scanning electron microscope (FE-SEM). The backscattered electron image obtained by observing with FE-SEM may be simply referred to as an SEM image.

[0028] When observing a cross section of the R-T-B sintered magnet 1 with SEM, as shown in FIG. 1, main phase particles 11 and a plurality of types of grain boundary phases existing at the grain boundaries can be seen. And, the plurality of types of grain boundary phases have shades of color according to the composition and shapes according to the crystal system, respectively.

[0029] For example, by performing point analysis on each grain boundary phase using an energy dispersive X-ray spectrometer (EDS) attached to a FE-SEM, an electron probe microanalyzer (EPMA), a transmission electron microscope (TEM), etc., and clarifying the composition, it is possible to identify what kind of grain boundary phases they are.

[0030] Furthermore, the crystal structure of each grain boundary phase may be confirmed by a transmission electron microscope (TEM). By confirming the crystal structure of each grain boundary phase using TEM, each grain boundary phase can be more clearly identified.

[0031] As shown in the SEM image of Fig. 1, the R-T-B sintered magnet 1 includes main phase particles 11 and grain boundaries existing between the main phase particles 11. The main phase particles 11 are composed of an R 2 T 14 B compound. The R 2 T 14 B compound is a compound having a crystal structure composed of a tetragonal crystal of the R 2 T 14 B type. The main phase particles 11 are black in the SEM image. There is no particular limitation on the size of the main phase particles 11, but the equivalent circle diameter is generally 1.0 μm to 10.0 μm.

[0032] The grain boundaries include multi-particle grain boundaries and two-particle grain boundaries. A multi-particle grain boundary is a grain boundary surrounded by three or more main phase particles, and a two-particle grain boundary is a grain boundary existing between two adjacent main phase particles.

[0033] The grain boundaries contain at least two types of grain boundary phases. In Fig. 1, they include an R-T phase 13 and an R-rich phase 15. When comparing the brightness in the SEM image among the main phase particles 11, the R-T phase 13, and the R-rich phase 15, the main phase particles 11 are the darkest and the R-rich phase 15 is the brightest.

[0034] In the R-T phase 13, the content ratio of R to T is approximately 1:2 in terms of atomic ratio. Specifically, the content of R is 20.0 at% or more and 40.0 at% or less, and the content of T is 55.0 at% or more and 80.0 at% or less. And the total content of elements other than R and T contained in the R-T phase 13 is 10.0 at% or less. Note that the contents of R, T, and elements other than R and T are the contents excluding oxygen (O), carbon (C), and nitrogen (N).

[0035] The R-rich phase 15 refers to a phase in which the content of R is 40.0 at% or more and the content of T is lower than that in the R-T phase 13. The content of T may be 55.0 at% or less. Note that the contents of R and T are the contents excluding O, C, and N.

[0036] In a cross-section of an R-T-B sintered magnet, taking the area ratio of the R-T phase 13 to the grain boundary as S(R-T), S(R-T) is 0.60 or more and 0.85 or less.

[0037] The inventors have found that in an R-T-B sintered magnet using Ce, which is a rare earth element with low cost but reduces HcJ compared to Nd and Pr, by setting S(R-T) within the above range, HcJ is improved. The mechanism by which HcJ is improved when S(R-T) is within the above range has not been fully elucidated. The inventors speculate the following mechanism.

[0038] The R-rich phase 15 promotes the magnetic segmentation of the main phase particles 11. As a result, by including the R-rich phase 15, HcJ can be improved.

[0039] In the R-T phase 13, the content of Ce with respect to the total content of R is likely to be larger than that in the main phase particles 11. This is to discharge Ce from the main phase particles 11 when the R-T phase 13 is formed. As a result, the content of R other than Ce in the main phase particles 11, specifically Nd, increases. And the anisotropy magnetic field in the main phase particles 11 increases.

[0040] When the above-mentioned R-rich phase 15 and R-T phase 13 are included such that S(R-T) is 0.60 or more and 0.85 or less, the effect of promoting the magnetic disconnection of the main phase particles 11 and the effect of discharging Ce from the main phase particles 11 are compatible. As a result, an R-T-B sintered magnet having a high HcJ is obtained.

[0041] In addition, although there is no particular limitation on the area ratio of the R-rich phase 15 to the grain boundary, it is preferable that the portion other than the R-T phase 13 at the grain boundary is the R-rich phase 15. Specifically, the area ratio of the phase other than the R-rich phase 15 and the R-T phase 13 to the grain boundary is preferably 10.0% or less (including 0%).

[0042] There is no particular limitation on the area of the observation range of the SEM image for calculating S(R-T), but a sufficiently wide range is set for calculating S(R-T). For example, the area of the observation range may be 0.01 mm 2 or more.

[0043] (Manufacturing method) Hereinafter, an example of a method for manufacturing an R-T-B sintered magnet will be described. The method for manufacturing an R-T-B sintered magnet includes the following steps.

[0044] (a) Alloy preparation step of producing an alloy for R-T-B sintered magnet (raw material alloy) (b) Crushing step of crushing the raw material alloy (c) Molding step of molding the obtained alloy powder (d) Sintering step of sintering the molded body to obtain an R-T-B sintered magnet (e) Aging treatment step of aging the R-T-B sintered magnet (f) Processing step of processing the R-T-B sintered magnet (g) Grain boundary diffusion step of diffusing a heavy rare earth element into the grain boundary of the R-T-B sintered magnet (h) Surface treatment step of surface-treating the R-T-B sintered magnet

[0045] [Alloy preparation step] Prepare an alloy for an R-T-B sintered magnet (alloy preparation step). Hereinafter, as an example of the alloy preparation method, the strip casting method will be described, but the alloy preparation method is not limited to the strip casting method.

[0046] Prepare raw materials corresponding to the composition of the R-T-B sintered magnet, and melt the prepared raw materials in an inert gas atmosphere such as vacuum or Ar gas. Then, by casting the melted raw materials, a raw material alloy that becomes the raw material of the R-T-B sintered magnet is produced. In the following description, although the one-alloy method will be described, a two-alloy method in which the first alloy and the second alloy are mixed to produce raw material powder may also be used.

[0047] There is no particular limitation on the type of raw material metal. For example, rare earth metals, pure iron, pure cobalt, and further compounds such as ferroboron (FeB), and alloys such as rare earth alloys can be used. There is no particular limitation on the casting method for casting the raw material metal. For example, ingot casting method, strip casting method, book mold method, centrifugal casting method, etc. can be mentioned. If the obtained raw material alloy has solidification segregation, homogenization treatment (solution treatment) may be performed as necessary.

[0048] [Grinding step] After producing the raw material alloy, the raw material alloy is ground (grinding step). The grinding step may be performed in two stages, a coarse grinding step of grinding until the particle size becomes about several hundred μm to several mm, and a fine grinding step of fine grinding until the particle size becomes about several μm, or may be performed in one stage with only the fine grinding step.

[0049] (Coarse grinding step) Coarsely grind the raw material alloy until the particle size becomes about several hundred μm to several mm (coarse grinding step). Thereby, a coarsely ground powder of the raw material alloy is obtained. Coarse grinding can be performed, for example, by occluding hydrogen in the raw material alloy and then releasing hydrogen based on the difference in hydrogen occlusion amount between different phases to cause self-disintegrating grinding (hydrogen occlusion grinding). There is no particular limitation on the conditions for dehydrogenation, but for example, dehydrogenation is performed at 300 to 650 °C in an argon (Ar) flow or in a vacuum.

[0050] The method of coarse pulverization is not limited to the above hydrogen storage pulverization. For example, in an inert gas atmosphere, coarse pulverization may be performed using a coarse pulverizer such as a stamp mill, jaw crusher, or brown mill.

[0051] In order to obtain an R-T-B sintered magnet having high magnetic properties, the atmosphere in each step from the coarse pulverization step to the sintering step described later is preferably an atmosphere with a low oxygen concentration. The oxygen concentration is adjusted by controlling the atmosphere in each manufacturing step and the like. If the oxygen concentration in each manufacturing step is high, rare earth elements in the alloy powder obtained by pulverizing the raw material alloy will oxidize to form R oxides. The R oxides are not reduced during sintering and precipitate at the grain boundaries as R oxides. As a result, the coercivity HcJ of the obtained R-T-B sintered magnet tends to decrease. Therefore, for example, each step (fine pulverization step, molding step) is preferably carried out in an atmosphere with an oxygen concentration of 100 ppm or less.

[0052] (Fine pulverization step) After the raw material alloy is coarsely pulverized, the coarsely pulverized powder of the obtained raw material alloy is finely pulverized until the average particle diameter becomes about several μm (fine pulverization step). Thereby, a finely pulverized powder of the raw material alloy can be obtained. There is no particular limitation on the D50 of the particles contained in the finely pulverized powder. For example, the D50 may be 1.0 μm or more and 10.0 μm or less.

[0053] Fine pulverization is carried out by further pulverizing the coarsely pulverized powder using a fine pulverizer such as an air jet mill (jet mill) while appropriately adjusting conditions such as pulverization time. Hereinafter, the jet mill will be described. A jet mill generates a high-speed gas flow by discharging a high-pressure inert gas (for example, He gas, N 2 gas, Ar gas) from a narrow nozzle, and accelerates the coarsely pulverized powder of the raw material alloy by this high-speed gas flow to cause collisions between the coarsely pulverized powders of the raw material alloy and collisions with the target or the container wall for pulverization.

[0054] When finely pulverizing the coarsely pulverized powder of the raw material alloy, a lubricant, for example, an organic lubricant or a solid lubricant, may be added. Examples of the organic lubricant include oleic acid amide, lauric acid amide, zinc stearate, etc. Examples of the solid lubricant include graphite, etc. By adding a lubricant, it is possible to obtain a finely pulverized powder in which orientation is likely to occur when a magnetic field is applied in the molding process. Either only one of the organic lubricant and the solid lubricant may be used, or both may be mixed and used.

[0055] [Molding process] The finely pulverized powder is molded into the desired shape (molding process). In the molding process, the finely pulverized powder is filled into a mold placed in a magnetic field and pressurized to mold the finely pulverized powder and obtain a molded body. At this time, by molding while applying a magnetic field, it is possible to mold the finely pulverized powder with the crystal axes oriented in a specific direction. Since the obtained molded body is oriented in a specific direction, an R-T-B sintered magnet having stronger anisotropy in magnetism can be obtained. A molding aid may be added during molding. There is no particular limitation on the type of the molding aid. The above lubricant may be used.

[0056] The pressure during pressurization may be, for example, 30 MPa or more and 300 MPa or less. The magnetic field to be applied may be, for example, 1.0 T or more and 5.0 T or less. The magnetic field to be applied is not limited to a static magnetic field and may be a pulsed magnetic field. Also, a static magnetic field and a pulsed magnetic field may be used in combination.

[0057] In addition, as the molding method, in addition to the dry molding in which the finely pulverized powder is directly molded as described above, wet molding in which a slurry in which the finely pulverized powder is dispersed in a solvent such as oil is molded can also be applied.

[0058] The shape of the molded body obtained by molding the finely pulverized powder is not particularly limited, and can be, for example, a shape corresponding to the desired shape of the R-T-B sintered magnet such as a rectangular parallelepiped, a flat plate shape, a columnar shape, a ring shape, a C shape, etc.

[0059] [Sintering process] The obtained compact is sintered in a vacuum or an inert gas atmosphere to obtain an R-T-B sintered magnet (sintering step). The sintering temperature needs to be adjusted according to various conditions such as composition, pulverization method, differences in particle size and particle size distribution. There is no particular limitation on the sintering temperature, but for example, it may be 950 °C or higher and 1100 °C or lower. There is no particular limitation on the sintering time, but for example, it may be 2 hours or longer and 10 hours or shorter. There is no particular limitation on the atmosphere during sintering. For example, an inert gas atmosphere may be used, or a vacuum atmosphere of less than 100 Pa may be used.

[0060] [Aging treatment step] After sintering the compact, the R-T-B sintered magnet is subjected to aging treatment (aging treatment step). After sintering, the obtained R-T-B sintered magnet is subjected to aging treatment at a temperature lower than that during sintering.

[0061] In the aging treatment, the aging temperature is 550 °C or higher and 650 °C or lower, and the aging time is 10 minutes or longer and 300 minutes or shorter. When Ce is included as R and the content of Ce relative to the total content of R is 15 mass% or more and 35 mass% or less, by performing aging treatment under the above conditions, it becomes easier to keep S(R-T) within a predetermined range.

[0062] When the aging temperature is too low, S(R-T) tends to become too large. When the aging temperature is too high, S(R-T) tends to become too small. In either case, HcJ cannot be improved. Also, when the aging temperature is too high, even in the bright phase that appears as the R-T phase in the SEM image, when actually performing point analysis, the abundance ratio of R and T often deviates greatly from 1:2 and is not the R-T phase in many cases.

[0063] There is no particular limitation on the atmosphere during aging treatment. For example, an inert gas atmosphere at a pressure of atmospheric pressure or higher (for example, He gas, Ar gas) may be used. Also, the aging treatment step may be performed after the processing step described later.

[0064] [Processing step] The obtained R-T-B sintered magnet may be processed into a desired shape as necessary (processing step). Examples of the processing method include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing.

[0065] [Grain boundary diffusion step] For the grain boundaries of the processed R-T-B sintered magnet, a heavy rare earth element may be further diffused (grain boundary diffusion step). There is no particular limitation on the method of grain boundary diffusion. For example, it may be carried out by attaching a compound containing a heavy rare earth element to the surface of the R-T-B sintered magnet by coating or vapor deposition and then performing heat treatment. Alternatively, it may be carried out by performing heat treatment on the R-T-B sintered magnet in an atmosphere containing vapor of a heavy rare earth element. By grain boundary diffusion, the HcJ of the R-T-B sintered magnet can be further improved.

[0066] [Surface treatment step] The R-T-B sintered magnet obtained by the above steps may be subjected to surface treatment such as plating, resin coating, oxidation treatment, and chemical conversion treatment (surface treatment step). Thereby, the corrosion resistance can be further improved.

[0067] In the above manufacturing method, the processing step, the grain boundary diffusion step, and the surface treatment step are carried out, but these steps are not necessarily required to be carried out.

[0068] The R-T-B sintered magnet obtained as described above is an R-T-B sintered magnet that contains Ce and has good HcJ.

[0069] The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. For example, it may be a permanent magnet. That is, if it contains Ce within a predetermined range, contains an R-rich phase and an R-T phase, and S(R-T) is 0.60 or more and 0.85 or less, it may be a permanent magnet other than a sintered magnet.

[0070] The R-T-B permanent magnet of the present invention can be used for general applications of R-T-B permanent magnets. For example, it can be used for rotators of automobiles.

Example

[0071] Hereinafter, the invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0072] (Alloy Preparation Step) Alloys A to F with the compositions shown in Table 1 were prepared as raw materials alloys. Note that TRE means the total content of rare earth elements. The content of rare earth elements not listed in Table 1 is less than 0.01% by mass in total.

[0073] First, raw materials metals having predetermined elements were prepared. As the raw materials metals, Nd, Pr, Ce, Fe, Co, FeB, Al, Cu, Zr, and Ga with a purity of 99.9% each were prepared.

[0074] Next, these raw materials metals were weighed so as to obtain an alloy with the composition shown in Table 1, and a thin plate-shaped raw materials alloy with the composition shown in Table 1 was prepared by the strip casting method. Then, the alloys shown in Table 2 were selected as raw materials alloys for each sample.

[0075] (Grinding Step) The raw materials alloy obtained in the alloy preparation step was ground to obtain alloy powder. Grinding was performed in two stages: coarse grinding and fine grinding. Coarse grinding was performed by hydrogen storage grinding. After hydrogen was absorbed by the raw materials alloy at room temperature, dehydrogenation was performed at 600 °C for 5 hours in an Ar flow. By coarse grinding, alloy powder with a particle size of about several hundred μm to several mm was obtained.

[0076] Fine grinding was performed by adding 0.1 part by mass of oleic acid amide as a lubricant to 100 parts by mass of the alloy powder obtained by coarse grinding, mixing them, and then performing the grinding in a high-pressure nitrogen gas atmosphere using a jet mill. Fine grinding was performed until the D50 of the alloy powder reached about 3.5 μm.

[0077] (Forming Step) The mixed powder obtained by the pulverization process was formed in a magnetic field to obtain a formed body. After filling the mixed powder into a mold placed between electromagnets, it was pressed and formed while applying a magnetic field by the electromagnets. Specifically, the mixed powder was compacted at a pressure of 110 MPa in a magnetic field of 2.2 T. The direction in which the magnetic field was applied was perpendicular to the pressing direction.

[0078] (Sintering process) The obtained formed body was sintered to obtain a sintered body. A sintered body was obtained with a sintering temperature of 1000 °C and a sintering time of 4 hours. The atmosphere during sintering was a vacuum atmosphere.

[0079] (Aging process) The obtained sintered body was subjected to aging treatment to obtain an R-T-B-based sintered magnet. The aging treatment was performed with an aging temperature as the temperature described in Table 2 and an aging time of 1.5 hours.

[0080] (Evaluation) That the composition of the finally obtained R-T-B-based sintered magnet in each example and comparative example was the same as the composition of the raw material alloy, that is, the composition shown in Table 1, was confirmed by compositional analysis using fluorescent X-ray analysis, inductively coupled plasma mass spectrometry (ICP method), and gas analysis.

[0081] The magnetic properties of the R-T-B-based sintered magnets prepared from the raw material alloys of each example and comparative example were measured using a B-H tracer. As the magnetic property, HcJ was measured at room temperature. The results are shown in Table 2. HcJ of 1400 kA / m or more was regarded as good.

[0082] Hereinafter, the calculation method of the calculated value of the anisotropy magnetic field (Ha) calculated from the composition of each R-T-B-based sintered magnet will be described.

[0083] First, the composition of each alloy described in Table 1 is converted to atomic%. The converted results are shown in Table 3.

[0084] Next, for the composition of each alloy, the atomic ratio of the content of each rare earth element to the total content of rare earth elements is calculated. The calculated results are shown in Table 4.

[0085] Nd 2 Fe 14 B crystal, Pr 2 Fe 14 B crystal, Ce 2 Fe 14 When there is one kind of R such as B crystal, etc., R 2 Fe 14 The literature value of Ha of the B crystal is known. The literature values are shown in Table 4.

[0086] And for each R containing each rare earth element 2 Fe 14 The value obtained by multiplying the literature value of Ha of the B crystal by the atomic number ratio of each rare earth element is summed up, and for each R 2 Fe 14 The calculated value of Ha calculated from the composition of the B alloy is calculated. The calculated results are described in Table 4. Also, the calculated values of Ha are appropriately described in Tables 1 and 2.

[0087] In this example, the ratio of HcJ to the calculated value of Ha was calculated. That is, for the calculated value of Ha of the R 2 T 14 The ratio of HcJ of the actually obtained R-T-B sintered magnet to the calculated value of Ha of the B alloy was evaluated. The results are described in Table 2. HcJ / Ha of 28.00% or more was regarded as good, and 29.75% or more was regarded as even better. It can be said that the higher the HcJ / Ha, the more efficiently the coercivity is improved.

[0088] Regarding the calculation of the area ratio S(R-T) of the R-T phase to the grain boundary, it was performed by the following method.

[0089] First, the R-T-B sintered magnet was embedded in an epoxy resin. Then, the R-T-B sintered magnet was cut, and the obtained cross-section was polished. Commercially available abrasive papers were used for polishing. Specifically, a plurality of commercially available abrasive papers with numbers ranging from 180 to 2000 were prepared. Then, the cross-section of the R-T-B sintered magnet was polished in order from the abrasive paper with a lower number. Finally, polishing was performed using a buff and diamond abrasive grains. Note that no liquid such as water was used during polishing. This is to avoid corrosion of the components contained in the grain boundary.

[0090] Ion milling treatment was performed on the cross-section of the obtained sintered body to remove the influence of the outermost oxide film, nitride film, etc. Next, the cross-section of the sintered body was observed using FE-SEM. The observation magnification was set to 1000 times. From the contrast of the backscattered electron image obtained by the observation, it was confirmed that the main phase particles and grain boundaries were included, and it was confirmed that a plurality of types of grain boundary phases were included in the grain boundaries (multi-particle grain boundaries). In addition, by appropriately performing point analysis using EDS attached to FE-SEM on the grain boundary phase, it was confirmed that the R-rich phase and R-T phase were included in the grain boundaries in the experimental examples other than Comparative Example 2. The R-T phase was not included in Comparative Example 2. In the point analysis, the contents of the elements intentionally added during the production of the raw material alloy, that is, the elements listed in Table 1, were analyzed. And the area ratio S(R-T) of the R-T phase to the grain boundary was calculated. The results are shown in Table 2. Note that Fig. 1 is the backscattered electron image of Example 1, Fig. 2 is that of Comparative Example 2, Fig. 3 is that of Comparative Example 3, and Fig. 4 is that of Comparative Example 4.

[0091]

Table 1

[0092]

Table 2

[0093]

Table 3

[0094]

Table 4

[0095] (Examples 1 to 3, Comparative Examples 1, 2) Examples 1 to 3 and Comparative Examples 1 and 2 are all samples that were carried out under the same conditions except that the raw material alloys used were the same and the aging temperature was changed. The calculated values of Ha are also all the same.

[0096] In Examples 1 to 3 where the Ce content with respect to the total R content was 15% by mass or more and 35% by mass or less and the aging temperature was 550 to 650°C, S(R-T) was 0.60 or more and 0.85 or less. In contrast, in Comparative Example 1 where the aging temperature was as low as 400°C, S(R-T) increased. In Comparative Example 2 where the aging temperature was as high as 900°C, the R-T phase was not included. As a result, in Examples 1 to 3, HcJ and HcJ / Ha became higher compared to Comparative Examples 1 and 2.

[0097] (Examples 2, 4, 5, Comparative Example 3) Examples 4, 5, and Comparative Example 3 are samples obtained by mainly changing the Ce content with respect to the total R content for Example 2. The calculated value of Ha decreases as the Ce content increases.

[0098] In Examples 4 and 5 where the Ce content with respect to the total R content was 15% by mass or more and 35% by mass or less, S(R-T) was 0.60 or more and 0.85 or less, similar to Example 2. In contrast, in Comparative Example 3 where the Ce content with respect to the total R content was high, S(R-T) increased. As a result, HcJ / Ha became lower in Comparative Example 3 compared to Examples 2, 4, and 5.

[0099] Figure 5 is a graph in which Examples 2, 4, 5, and Comparative Example 3 are plotted with Ha on the horizontal axis and HcJ on the vertical axis, and further lines of HcJ / Ha = 28.00% and 29.75% are drawn. Each example has a large HcJ / Ha, while the comparative example has a small HcJ / Ha.

[0100] (Examples 2, 6, Comparative Example 4) Examples 6 and Comparative Example 4 are samples obtained by mainly changing the Ga content for Example 2. The calculated values of Ha are all the same.

[0101] The higher the Ga content, the smaller S(R-T) became. In Examples 2 and 6 where S(R-T) was 0.60 or more and 0.85 or less, HcJ and HcJ / Ha became higher compared to Comparative Example 4 where S(R-T) was small.

Description of Reference Signs

[0102] 1... R-T-B series sintered magnet 11... main phase particle 13... R-T phase 15... R-rich phase

Claims

1. R 2 T 14 An R-T-B-based permanent magnet comprising a main-phase particle composed of a B compound (wherein R is a rare-earth element, T is a transition metal element, and B is boron) and a grain boundary R contains Ce, assuming the total of the R-T-B based permanent magnet is 100% by mass, the Co content is 0.50% by mass or more and 3.00% by mass or less, the Ce content with respect to the total content of R in the R-T-B based permanent magnet is 15% by mass or more and 35% by mass or less, the grain boundary contains an R-rich phase and an R-T phase, In a cross-section of the R-T-B based permanent magnet, with the area ratio of the R-T phase to the grain boundary being S(R-T), an R-T-B based permanent magnet where S(R-T) is 0.60 or more and 0.85 or less.

2. The R-T-B based permanent magnet according to Claim 1, wherein the Ga content is 0% by mass or more and 0.2% by mass or less.

3. The R-T-B based permanent magnet according to Claim 1 or 2, which substantially does not contain La and Y.

4. assuming the total of the R-T-B based permanent magnet is 100% by mass, the total content of R is 30.00% by mass or more and 34.00% by mass or less, the B content is 0.70% by mass or more and 0.95% by mass or less, the Co content is 0.50% by mass or more and 3.00% by mass or less, the Ga content is 0% by mass or more and 0.60% by mass or less, the Al content is 0.20% by mass or more and 1.00% by mass or less, the Cu content is 0% by mass or more and 0.50% by mass or less, the Zr content is 0.10% by mass or more and 1.00% by mass or less, Fe is the substantial remainder, The R-T-B based permanent magnet according to any one of Claims 1 to 3, wherein the Ce content with respect to R in the R-T-B based permanent magnet is 15% by mass or more and 25% by mass or less.

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