RTB-based sintered magnet

Abstract

RTB-based sintered magnet comprising an RTB-based mixture as main phase grains, wherein R represents at least one rare earth element, T represents one or more elements from the iron group, including Fe or the combination of Fe and Co, the RT-β-based sintered magnet comprises 0.75 wt% to 0.84 wt% B, 0.1 wt% to 0.3 wt% C, 0.01 wt% to 0.2 wt% N, and a concentrated R-Ga-C region is present in the grain boundary formed between or below two or more adjacent main phase grains, and the concentrations of R, Ga and C in the concentrated R-Ga-C region are higher than those in the corresponding main phase grains.

Description

[0001] The present invention relates to an RTB-based sintered magnet comprising a rare earth element (R), one or more elements from the iron group (T) necessarily comprising Fe or the combination of Fe and Co and boron (B) as main components. BACKGROUND OF THE INVENTION

[0002] The RTB-based sintered magnet exhibits excellent magnetic properties and is therefore used in the voice coil motor (VCM) of a hard disk drive, various motors such as those in electric hybrid vehicles, household appliances, and the like. When an RTB-based sintered magnet is used in a motor or similar device, excellent heat resistance and high coercivity are necessary so that the magnet can adapt to operating conditions at higher temperatures.

[0003] To increase the coercive field strength (HcJ) of the RTB-based sintered magnet, a heavy rare-earth element such as Dy or Tb is used in a conventional manner to partially replace the rare-earth element R, with the main use being the light rare-earth element such as Nd or Pr to improve the magnetocrystalline anisotropy of the R2T. 14 To improve the B-phase. So far, it has proven difficult to produce a magnet whose coercive field strength is sufficient for a motor or the like without using a heavy rare-earth element.

[0004] Compared to Nd or Pr, however, there are fewer raw material sources for Dy or Tb, making the latter more expensive. Recently, the supply of Dy and Tb has proven quite unstable due to the increasing demand for RTB-based sintered magnets with high coercivity, which use these elements in large quantities. Thus, in motor applications, a high coercivity is required even when a material composition is used in which the use of Dy or Tb is significantly reduced.

[0005] Typically, the crystal grains in RTB-based sintered magnets are micronized to increase the coercive field strength. For example, patent document 1 below discloses that the coercive field strength is improved by setting the average grain size of the main phase grains in the NdFeB-based sintered magnet to 4.5 µm or smaller, setting the carbon content in the entire NdFeB-based sintered magnet to 1000 ppm or less, and setting the ratio of the total volume of the carbon-rich phases in the triple points to the rare-earth-rich phases in the NdFeB-based sintered magnet to 50% or less.

[0006] To micronize the crystal grains in RTB-based sintered magnets, the particle size of the finely powdered raw material must be reduced. However, reducing the particle size of the finely powdered particles tends to make it more difficult for the crystals to orient themselves during a pressing step with an applied external magnetic field. Therefore, some countermeasures can be taken. For example, the amount of lubricant added to the finely powdered particles is increased. Alternatively, the finely powdered particles are mixed with an organic solvent to form a slurry, followed by a wet pressing step. In both cases, however, a problem arises: the carbon content in the RTB-based sintered magnet increases after sintering, and the coercivity decreases.In particular, the smaller the particle size, the larger the specific surface area in the pulverized particles. This tends to increase the carbon content, leading to a technical problem in that micronization does not sufficiently improve the coercive field strength.

[0007] Patent document 1 demonstrated that, without heating for dehydration during hydrogen storage pulverization, the hydrogen-based mixture will remain within the alloy powder particles. Furthermore, the carbon content in the sintered magnet can decrease with the generation of hydrogen. However, if a large amount of hydrogen remains within the alloy powder particles, a technical problem arises: the volume change during hydrogen release during the sintering process increases, and cracks are likely to form in the sintered magnet.

[0008] Patent document 2 describes how the decrease in coercive field strength can be inhibited by converting the carbon contained in the R-Fe-B-based magnetic alloy into carbides with one, two, or more types of elements from the group consisting of Cr, Mo, Nb, Ta, Ti, V, W, and Zr, and then precipitating the carbides in the magnetic alloy. However, this process presents problems because the carbides, which have no influence on the magnetic properties, must be precipitated in large quantities, resulting in a decrease in the residual magnetic flux density in the finished magnet.

[0009] The publication DE 11 2014 003 674 T5 describes an RTB-based sintered magnet and a motor. PATENT DOCUMENTS Patent Document 1: JP 5 400 255 B1 Patent document 2: JP H02 - 60 105 A BRIEF DESCRIPTION OF THE INVENTION

[0010] The present invention was developed taking into account the above-mentioned conditions, the object of which is to provide an RTB-based sintered magnet which has a high coercive field strength even when the carbon content is increased during the micronization of the finely powdered particles of the raw material.

[0011] To achieve the above-mentioned goal, the RTB-based sintered magnet of the present invention is characterized in that it contains an RTB-based composition as the main phase grains, wherein the above-mentioned RTB-based sintered magnet contains 0.1 wt% to 0.3 wt% C, and wherein a concentrated R-Ga-C region is present in the grain boundary formed between or below two or more adjacent main phase grains, and wherein the concentrations of R, Ga and C in the concentrated R-Ga-C region are higher than in the corresponding main phase grains.

[0012] With the RTB-based sintered magnets of the present invention mentioned above, a high coercive field strength can be achieved even when the particle size of the finely powdered particles is reduced and the carbon content in the sintered magnet is between 0.1 wt% and 0.3 wt%. In the conventional method for producing the RTB-based sintered magnet, the majority of the carbon reacts with the rare-earth-rich phases (referred to as R-rich phases) present at the grain boundary to form carbides. The RTB-based sintered magnet is a magnet produced by liquid-phase sintering, in which the sintering proceeds by converting the R-rich phases into a liquid phase, and the carbides do not convert into the liquid phase during the sintering process.Thus, the formation of carbides reduces the amount of rhodium-rich phases and results in a decrease in coercive field strength. In contrast, in the RTB-based sintered magnet of the present invention, the concentrated rhodium-Ga-carbon region formed at the grain boundary is a carbon-containing phase, which facilitates the generation of the liquid phase during sintering. Therefore, a sufficient liquid phase will be present during the sintering process, even with a high carbon content, thus providing a high coercive field strength.

[0013] In addition, the concentrated R-Ga-C region in the present invention further contains Cu, and the concentration of Cu in the concentrated R-Ga-C region is preferably higher than in the main phase grains. Since the concentrated R-Ga-C region contains Cu, the wetting between the concentrated R-Ga-C region and the main phase grains can be improved, and a thick two-grain interface phase tends to form. This will readily increase the coercive field strength.

[0014] In the present invention, the concentrated R-Ga-C region further contains Co. It is even preferred that the concentration of Co in the concentrated R-Ga-C region is higher than in the main phase grains. Due to the Co content in the concentrated R-Ga-C region, the coercive field strength tends to increase further.

[0015] The present invention makes it possible to provide an RTB-based magnet which exhibits a high coercive field strength even when the carbon content is increased during the micronization of the finely powdered particles of the raw material. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 schematically shows a backscattered electron image of the environment of a grain boundary which is surrounded by some main phase grains in the RTB-based sintered magnet of the present invention. Fig. Figure 2 shows a flowchart of an example of the method for manufacturing the RTB-based sintered magnet of the present invention. DETAILED DESCRIPTION OF THE EXECUTION FORMS

[0016] The present invention is described below with reference to the embodiments shown in the drawings. <R-T-B-basierter gesinterter Magnet>

[0017] The embodiments of the RTB-based sintered magnet according to the present invention are described. As in Fig. Figure 1 shows that the RTB-based sintered magnet in the present embodiment contains main phase grains 2 which consist of an RTB-based composition, wherein a concentrated R-Ga-C region is present in the grain boundary formed between or below two or more adjacent main phase grains, and the concentrations of R, Ga and C in the concentrated R-Ga-C region are higher than in the corresponding main phase grains.

[0018] The grain boundary contains a two-grain boundary phase 4, formed between two adjacent grains, and a triple point 6, formed between three or more main-phase grains. Additionally, the concentrated R-Ga-C region is the area present in the grain boundary formed between or beneath two or more adjacent main-phase grains, exhibiting concentrations of R, Ga, and C that are higher than those found in the corresponding main-phase grains. Other components may also be present in the concentrated R-Ga-C region, as long as R, Ga, and C are present as major components.

[0019] The concentrated R-Ga-C region preferably still contains Cu, and the concentration of Cu in the concentrated R-Ga-C region is higher than in the main phase grains. If the concentrated R-Ga-C region contains Cu as described above, the wetting between the concentrated R-Ga-C region and the main phase grains is improved, and a two-grain boundary phase is more likely to form. This simply increases the coercive field strength.

[0020] The concentrated R-Ga-C region preferentially retains Co, and the concentration of Co in the concentrated R-Ga-C region is higher than in the main phase grains. Because the concentrated R-Ga-C region contains Co, the coercive field strength tends to increase more readily.

[0021] The RTB-based sintered magnet in the present embodiment is a sintered body formed using an RTB-based alloy. The RTB-based sintered magnet of the present embodiment contains main phase grains composed of an RTB-based composition, wherein the grain boundaries have a higher R-value than the main phase grains.

[0022] R represents at least one rare-earth element. The rare-earth element refers to Sc, Y, and the lanthanide elements, which belong to group 3 of a long-period periodic table. The lanthanide group includes, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. Rare-earth elements are classified as light rare-earth elements and heavy rare-earth elements. Heavy rare-earth elements (hereinafter referred to as RH) refer to Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, while light rare-earth elements (hereinafter referred to as RL) refer to the other rare-earth elements.

[0023] In the present embodiment, T represents one or more elements of the iron group, including Fe or the combination of Fe and Co. T can be exclusively Fe or a type of Fe that has been partially replaced by Co. If Fe is partially replaced by Co, the temperature properties can be improved without deteriorating the magnetic properties.

[0024] In the RTB-based sintered magnet of the present invention, a portion of B can be replaced by carbon (C). This simplifies the manufacture of the magnet and reduces production costs. The amount of C used as a replacement for B is essentially an amount that has no effect on the magnetic properties.

[0025] The RTB-based sintered magnet of the present embodiment can also contain various well-known additive elements. In particular, it can contain at least one element from the group consisting of Ti, V, Cu, Cr, Mn, Ni, Zr, Nb, Mo, Hf, Ta, W, Al, Ga, Si, Bi and Sn.

[0026] The main phase grains contained in the RTB-based sintered magnets of the present invention are composed of an RTB-based composition, and this RTB-based composition is a type of composition whose crystal structure consists of tetragonal R2T 14 B is formed.

[0027] In the present embodiment, the cross-sectional area of ​​each main phase grain in a cross-section inside the RTB-based sintered magnet, which lies parallel to the C-axis, is calculated using a method based on image processing, wherein the diameter of a circle with said cross-sectional area (i.e., the equivalent diameter of the circle) is defined as the grain size of the main phase grain in that cross-section. Furthermore, the grain size of the main phase grain (whose cross-sectional area is cumulatively 50% of the total cross-sectional area accumulated from the main phase grain with a small cross-sectional area) is defined as the average grain size of the main phase grain.

[0028] The average grain size of the main phase grains contained in the sintered magnet of the RTB-based composition in the present invention is preferably 4.0 µm or less. If the average grain size of the main phase grains is greater than 4.0 µm, the coercive field strength tends to decrease. Furthermore, it is preferred that the average grain size of the main phase grains is in the range of 1.5 µm to 3.0 µm. A higher coercive field strength is likely to be achieved in such a range.

[0029] The RTB-based sintered magnet of the present invention contains at least the concentrated R-Ga-C region. In addition to the concentrated R-Ga-C region, it may also contain the R-rich phase with R as the main component, the B-rich phase with a higher concentration of boron (B), the concentrated ROCN region with higher concentrations of R, O, C and N than in the main phase grains, or the like.

[0030] The proportion of rhodium (R) in the RTB-based sintered magnet of the present embodiment is 25% by mass or more and 35% by mass or less, preferably 29% by mass or more and 34% by mass or less. If the proportion of rhodium is below 25% by mass, the production of the RTB-based composition, which constitutes the main phase of the RTB-based sintered magnet, is insufficient. Consequently, soft magnetic material such as α-Fe may be deposited, potentially degrading the magnetic properties. To reduce costs and avoid raw material shortages, the proportion of the heavy rare-earth element R in the present embodiment can be 1.0% by mass or less.

[0031] The proportion of B in the RTB-based sintered magnet of the present embodiment is 0.5 wt% or more and 1.5 wt% or less. The coercive field strength HcJ tends to decrease when the proportion of B is less than 0.5 wt%, while the residual magnetic flux density Br tends to decrease when the proportion of B is more than 1.5 wt%. Preferably, the proportion of B is 0.75 wt% or more and 0.95 wt% or less. In particular, when the proportion of B is in the range of 0.75 wt% to 0.95 wt%, the concentrated R-Ga-C region is more easily formed.

[0032] As described above, T represents one or more elements of the iron group, including Fe, or the combination of Fe and Co. If Co is included as T, the proportion of Co is preferably 0.3 wt% or more and 4.0 wt% or less, more preferably 0.5 wt% or more and 1.5 wt% or less. If the proportion of Co exceeds 4 wt%, the residual magnetic flux density tends to decrease. The RTB-based sintered magnet of the present embodiment also tends to become more expensive. Conversely, if the proportion of Co is less than 0.3 wt%, the corrosion resistance tends to deteriorate. The proportion of Fe in the RTB-based sintered magnet according to the present embodiment continues to represent essentially the remaining component of the RTB-based sintered magnet.

[0033] The RTB-based sintered magnet of the present embodiment preferably contains Cu, and the proportion of Cu is preferably 0.05 to 1.5 wt%, more preferably 0.15 to 0.6 wt%. With the inclusion of Cu, the resulting magnet will exhibit high coercivity and high corrosion resistance, and its temperature properties will also be improved. In addition, the residual magnetic flux density tends to decrease when the proportion of Cu exceeds 1.5 wt%. Conversely, the coercivity tends to decrease when the proportion of Cu is less than 0.05 wt%.

[0034] The RTB-based sintered magnet of the present embodiment contains Ga, and the proportion of Ga is preferably 0.05 wt% to 1.5 wt%, more preferably 0.15 wt% to 1.0 wt%. With the inclusion of Ga, the magnet obtained will exhibit high coercivity and high corrosion resistance, and its temperature properties will also be improved. In addition, the residual magnetic flux density tends to decrease when the proportion of Ga exceeds 1.5 wt%. Conversely, if the proportion of Ga is less than 0.05 wt%, the formation of the concentrated R-Ga-C region becomes more difficult, and the magnetic properties tend to deteriorate.

[0035] The RTB-based sintered magnet of the present embodiment preferably contains aluminum. With aluminum, the magnet obtained exhibits high coercivity and high corrosion resistance, and its temperature properties are also improved. The proportion of aluminum is preferably 0.03% by mass or more and 0.6% by mass or less, more preferably 0.10% by mass or more and 0.4% by mass or less.

[0036] The RTB-based sintered magnet of the present embodiment preferably contains Zr. The Zr creates effects that prevent grain growth during sintering, and excess carbon is fixed as a ZrC phase. The proportion of Zr is preferably 0.2 wt% or more and 1.5 wt% or less.

[0037] In the present embodiment, the RTB-based sintered magnet can also contain additive elements other than those mentioned above. In particular, Ti, V, Cr, Mn, Ni, Nb, Mo, Hf, Ta, W, Si, Bi, Sn and the like can be listed.

[0038] In the present embodiment, a certain amount of oxygen (O) may be present in the RTB-based sintered magnet. This certain amount depends on other parameters and can be determined in a suitable manner. From the point of view of corrosion resistance, the proportion of oxygen is preferably 0.05% by mass or more, and from the point of view of magnetic properties, preferably 0.2% by mass or less.

[0039] In the RTB-based sintered magnet of the present embodiment, carbon (C) is present in an amount of 0.1 wt% to 0.3 wt%. The RTB-based sintered magnet can be easily formed by including 0.1 wt% or more carbon in the magnet. When carbon is present in such an amount in a conventional RTB-based sintered magnet, the coercive field strength tends to decrease. However, in the RTB-based sintered magnet of the present embodiment, no decrease in coercive field strength was observed during the formation of the concentrated R-Ga-C region. Conversely, when the carbon content exceeds 0.3 wt%, the coercive field strength tends to decrease, even when the concentrated R-Ga-C region is formed.

[0040] Additionally, a certain amount of nitrogen (N) is contained in the RTB-based sintered magnet in the present embodiment. This amount depends on other parameters and can be determined in a suitable manner. From the standpoint of magnetic properties, the nitrogen content is preferably 0.01 to 0.2% by mass.

[0041] Well-established methods can be used to measure the oxygen, carbon, and nitrogen content in RTB-based sintered magnets. For example, the oxygen content can be measured using a non-dispersive inert gas melt infrared absorption method, and the carbon content can be measured by combustion in an oxygen-airflow infrared absorption method. Additionally, the nitrogen content can be measured using an inert gas melt thermal conductivity method.

[0042] The RTB-based sintered magnet of the present embodiment features the concentrated R-Ga-C region at the grain boundary, wherein the concentrated R-Ga-C region exhibits higher concentrations of R, Ga, and C than the main phase grains. In addition, as described above, the concentrated R-Ga-C region consists mainly of R, Ga, and C, but may also contain other components. For example, Cu, Co, Fe, and the like may be present as elements within the concentrated R-Ga-C region.

[0043] As described above, the formation of the concentrated R-Ga-C region at the grain boundary results in a high coercive field strength, even when the carbon content is high, such as 0.1 wt% to 0.3 wt%. In conventional RTB-based sintered magnets, the majority of the carbon reacts with the rhodium-rich phase at the grain boundary to form carbides when carbon is present in such a large quantity. RTB-based sintered magnets are produced by liquid-phase sintering, where the sintering process proceeds by converting the rhodium-rich phase into a liquid phase. During the sintering process, carbides do not convert into a liquid phase. Therefore, carbide formation reduces the amount of rhodium-rich phases and results in a decrease in coercive field strength.In particular, when the average grain size of the main phase grains is small, the specific surface area of ​​the main phase grains increases, and the liquid phase must be sufficiently abundant to achieve an adequate coercive field strength. Thus, the coercive field strength tends to decrease slightly with an increased carbon content. In contrast, the concentrated R-Ga-C region, which forms at the grain boundary in the RTB-based sintered magnet of the present embodiment, is a carbon-containing phase that promotes the generation of the liquid phase during sintering. Therefore, even with a high carbon content, the liquid phase will still be sufficiently present during sintering, and a high coercive field strength can be achieved.

[0044] The RTB-based sintered magnet of the present embodiment can be produced, for example, using the following method, as described below. In particular, in addition to the RTB-based starting alloy (a first alloy), which mainly forms the main phase, a second alloy can be added, which mainly forms the grain boundary. Furthermore, the manufacturing conditions in the production steps, such as the heating profile in the sintering step, can be controlled.

[0045] It is taken into account that the concentrated R-Ga-C region formed at the grain boundary of the RTB-based sintered magnet of the present embodiment is formed as follows. In particular, the R and Ga present in the second alloy form a composition with carbon of the carbon-based composition, which, after remaining at a specific temperature for a specific duration during the manufacturing process, is mixed during the sintering step. This composition is deposited at the grain boundary as a concentrated R-Ga-C region. Subsequently, to promote sintering, the concentrated R-Ga-C region transforms into the liquid phase at the sintering temperature and is redeposited during the cooling process.

[0046] The RTB-based sintered magnet of the present embodiment is typically used after machining into any desired shape. The shape of the RTB-based sintered magnet according to the present embodiment is not particularly limited and can have a columnar shape, such as the shape of a cuboid or hexahedron, a flat shape, the shape of a rectangular prism, and the like. The shape can also be cylindrical, with the cross-sectional shape of the RTB-based sintered magnet being C-shaped. The rectangular prism can be a prism whose base is rectangular or square.

[0047] In addition, the RTB-based sintered magnet of the present embodiment has both a magnetic product that has been magnetized in the present magnet after processing and a magnetic product that has not been magnetized in the present magnet. <Herstellungsverfahren des R-T-B-basierten gesinterten Magneten>

[0048] An example of the method for manufacturing the RTB-based sintered magnet of the present embodiment with the configuration mentioned above is described with reference to the drawings. Fig. Figure 2 shows a flowchart with an example of the manufacturing process of the RTB-based sintered magnet in the embodiment of the present invention. As shown in Fig. Figure 2 shows that the method for manufacturing the RTB-based sintered magnet in the present embodiment comprises the following steps: (a) an alloy preparation step in which a first alloy and a second alloy are prepared (step S11); (b) a pulverization step in which the first alloy and the second alloy are pulverized (step S12); (c) a mixing step in which the powder of the first alloy and the powder of the second alloy are mixed (step S13); (d) a compression step in which the mixed powder is compressed (step S14); (e) a sintering step in which the green body is sintered to provide an RTB-based sintered magnet (step S15); (f) an aging treatment step in which the RTB-based sintered magnet is subjected to an aging treatment (step S16); (g) a cooling step in which the RTB-based sintered magnet is cooled (step S17); (h) a processing step in which the RTB-based sintered magnet is processed (step 18); (i) a grain boundary diffusion step in which a heavy rare earth element is diffused into the grain boundary of the RTB-based sintered magnet (step 19) ; (j) a surface treatment step in which the RTB-based sintered magnet is subjected to a surface treatment (step 20). [Alloy preparation step: Step S11]

[0049] An alloy base (a first alloy), which mainly represents the main phase of the RTB-based sintered magnet of the present embodiment, and an alloy base (a second alloy), which mainly represents the grain boundary of the RTB-based sintered magnet of the present embodiment, are prepared (alloy preparation step (step S11)). In this alloy preparation step (step S11), the raw material metals are melted under vacuum or in an inert gas atmosphere such as argon, according to the composition of the RTB-based sintered magnet of the present embodiment. They are then cast to provide the first alloy and the second alloy with the respective desired compositions. Furthermore, a two-alloy process is described in the present embodiment in which the raw material powder is prepared by mixing the two alloys (i.e.,the first alloy and the second alloy). However, a single-alloy process can also be used, in which a single alloy is used instead of the first alloy and the second alloy.

[0050] The raw material can be, for example, a rare-earth element metal, a rare-earth element alloy, pure iron, ferroboron, or their alloys or compositions. The casting process for the raw material can be, for example, ingot casting, strip casting, book casting, centrifugal casting, or similar. If segregation occurs, the resulting raw material alloy should be homogenized if necessary. Homogenization of the raw material alloy is achieved by holding it under vacuum or in an inert gas atmosphere at a temperature of 700°C or higher and 1500°C or lower for one hour or more. During this process, the alloy for the RTB-based sintered magnet is melted and homogenized. [Powdering step: Step S12]

[0051] After the first and second alloys have been produced, they are pulverized (pulverization step (step S12)). In this pulverization step (step S12), following the production of the first and second alloys, the first and second alloys are pulverized separately to produce powder. The first and second alloys can also be pulverized together.

[0052] The pulverization step (step S12) includes a coarse pulverization step (step S12-1) in which the alloy is pulverized to a particle size of a few hundred µm to a few mm, and a fine pulverization step (step S12-2) in which the alloy is pulverized to a particle size of a few µm. (Coarse pulverization step (Step S12-1))

[0053] The first and second alloys are pulverized to a particle size of a few hundred µm to a few mm (coarse pulverization step (step S12-1)). In this way, the coarsely pulverized powders of the first and second alloys are obtained. The coarse pulverization can be carried out as follows: First, hydrogen is applied to the first and second alloys. Then, the hydrogen is released according to the difference in hydrogen storage capacity between the different phases. During hydrogen removal, pulverization occurs through self-collapse (hydrogen storage pulverization).

[0054] In addition to the hydrogen storage pulverization mentioned above, the coarse pulverization step (step S12-1) can also be carried out using a coarse pulverization device such as a crusher, jaw crusher, mill and the like in an inert gas atmosphere.

[0055] To ensure good magnetic properties, the atmosphere in each step, from the pulverization step (step S12) to the sintering step (step S15), preferably has a low oxygen concentration. The oxygen concentration can be adjusted in each manufacturing step by controlling the atmosphere. In the case of a high oxygen concentration in each manufacturing step, the rare earth element is oxidized in both the first and second alloy powders to generate r-oxides. The r-oxide is deposited at the grain boundary without being reduced during the sintering process, resulting in a decrease in br in the resulting RTB-based sintered magnet. The oxygen concentration in each step is therefore preferably, for example, 100 ppm or less. (Fine pulverization step: Step S12-2)

[0056] After the first and second alloys have been coarsely pulverized, the coarsely pulverized powder of the first and second alloys is finely pulverized to an average particle size of approximately a few micrometers (fine pulverization step (step S12-2)). In this way, finely pulverized powders of the first and second alloys are obtained. By further fine pulverization of the coarsely pulverized powder, a finely pulverized powder with particles of preferably 0.1 µm or more and 4.0 µm or less, and preferably 1.5 µm or more and 3.3 µm or less, can be obtained. If the average particle size of the finely pulverized powder is controlled within such a range, the average particle size in the sintered main-phase grains can be approximately 4.0 µm or less.

[0057] Even though the finely pulverized powder in the present embodiment is obtained by separately pulverizing the first alloy and the second alloy, the finely pulverized powder can still be obtained after mixing the coarsely pulverized powder of the first alloy and the coarsely pulverized powder of the second alloy in the fine pulverization step (step S12-2).

[0058] The fine pulverization step is achieved by appropriately adjusting conditions such as pulverization time, and simultaneously, the coarsely pulverized powder is further pulverized using a fine pulverization device such as a jet mill, ball mill, or similar instrument. In the jet mill, the following pulverization process takes place: In the jet mill, an inert gas (e.g., nitrogen gas) is discharged at high pressure from a narrow nozzle to generate a high-velocity gas stream. The coarsely pulverized powders of the first and second alloys are accelerated at high speed by this gas stream, resulting in collisions between the coarsely pulverized powders of the first and second alloys or between the coarsely pulverized powder and a target object or container wall.

[0059] Especially when a finely pulverized powder with a small particle size is obtained using a jet mill, the powder has a very active surface area. In this respect, it is highly likely that the powder will re-aggregate or accumulate on the container wall, with the yield tending to decrease. Therefore, by adding a pulverizing aid such as zinc stearate, oleamide, or the like during the fine pulverization of the coarsely pulverized powders of the first and second alloys, re-aggregation or accumulation on the container wall can be prevented. In this way, the finely pulverized powder can be obtained with a high yield. Additionally, adding such a pulverizing aid results in a finely pulverized powder that is easily oriented during the compaction step.The amount of pulverizing aid added depends on the particle size of the finely pulverized powder or the type of pulverizing aid, but is preferably approximately 0.1% by mass to 1% by mass. [Mixing step: Step S13]

[0060] After finely pulverizing the first and second alloys, the finely pulverized powders are mixed in an atmosphere with a low oxygen concentration (mixing step (step S13)). This yields a powder mixture. The atmosphere with a low oxygen concentration is an inert gas atmosphere such as nitrogen gas, argon gas, or the like. The mass ratio of the first alloy powder to the second alloy powder is preferably 80:20 or more and 97:3 or less, more preferably 90:10 or more and 97:3 or less.

[0061] Furthermore, the mass ratio of the first alloy powder to the second alloy powder is the same when they are pulverized together in the pulverization step (step S12) as when they are pulverized separately. The mass ratio of the first alloy powder to the second alloy powder is preferably 80:20 or more and 97:3 or less, more preferably 90:10 or more and 97:3 or less.

[0062] In the present embodiment, the first alloy and the second alloy preferably have different compositions. For example, the second alloy contains more Ga, Cu, and Co than the first alloy.

[0063] The proportion of Ga in the second alloy is preferably 0.2 wt% to 20 wt%, more preferably 0.5 wt% to 10 wt%. The first alloy may or may not contain Ga. If the first alloy also contains Ga, the proportion of Ga in the first alloy is preferably 0.2 wt% or less.

[0064] To improve orientation during the pressing step, a lubricant can also be added during the mixing step. [Pressure step: Step S14]

[0065] After the first alloy powder has been mixed with the second alloy powder, the mixture is compressed into a predetermined shape (compression step (step S14)). In the compression step (step S14), the powder mixed from the first and second alloy powders is placed in a mold surrounded by an electromagnet and then pressurized. This compresses the powder into a desired shape. A magnetic field is applied, creating a predetermined orientation in the raw material powder. The raw material powder is then compressed, orienting the crystal axis in a specific direction within the magnetic field. This produces a green compact. Because the resulting green compact is oriented in a specific direction, an anisotropic RTB-based sintered magnet with stronger magnetism can be produced.

[0066] The pressure applied during the pressing step is preferably 30 MPa to 300 MPa. The applied magnetic field preferably has a strength of 950 kA / m to 1600 kA / m. The applied magnetic field is not limited to a static magnetic field and can also be a pulsed magnetic field. Furthermore, a static magnetic field and a pulsed magnetic field can be used in combination.

[0067] In addition to the dry pressing process described above, in which the mixed powder is pressed directly, the pressing process can also be wet pressing, in which a sludge obtained by dispersing the raw material powder in a solvent such as an oil is pressed.

[0068] The shape of the green compact obtained by pressing the mixed powder is not particularly restricted, and it can be any shape such as a cuboid, a flat shape, a columnar shape, a ring-shaped shape and the like, according to the desired shape to be achieved for the RTB-based sintered magnet. [Sintering step: Step S15]

[0069] The green compact, which has been pressed into a predetermined shape in a magnetic field, is sintered under vacuum or in an inert gas atmosphere to produce an RTB-based sintered magnet (sintering step (step S15)). The green compact undergoes heat treatment under vacuum or in an inert gas atmosphere at temperatures of 900°C or higher and 1200°C or lower for one hour or more and 30 hours or less, respectively. This results in liquid-phase sintering of the mixed powder, yielding an RTB-based sintered magnet (a sintered body of an RTB-based sintered magnet) with an increased volume ratio occupied by the main phase.To provide an average grain size of the main phase grains of 4 µm or less, the sintering temperature and sintering time must be adjusted according to various conditions such as composition, pulverization process, particle size and particle size distribution.

[0070] To form the concentrated R-Ga-C region, a step is preferably added to the sintering step. In this added step, the green compact is held at a specific temperature before the temperature rises to the sintering temperature. The specific temperature in the additional step is preferably 500 to 700°C. The green compact is held at this specific temperature for preferably 30 minutes to 3 hours. It is considered that by adding a step with such conditions during the temperature rise process, the concentrated R-Ga-C region is formed based on the following basic mechanism. (1) Certain organic mixtures are present in the green compact, such as the pulverizing aid added during the pulverization step, the lubricant added during the mixing step, or the remaining components of the solvent used in wet pressing. These mixtures have not completely degraded thermally and remain as carbon-based components. (2) The finely powdered second alloy, containing R and Ga, generates hydrides in a preliminary stage of the sintering step through the hydrogen storage treatment in the coarse powdering step. In the step where the green compact is held at a certain temperature, the hydrogen evaporates. Since the second alloy, containing Ga, has a lower melting point than the first alloy, a liquid phase is generated when the hydrogen evaporates. (3) During the production of a liquid phase of the second alloy, reactions preferably occur between the carbon-based components mentioned in (1) and the components of the second alloy containing R and Ga, resulting in the deposition of the concentrated R-Ga-C region at the grain boundary.

[0071] After the green compact has been sintered, the sintered body is preferably cooled rapidly from the point of view of increased productivity. [Aging treatment step: Step S16]

[0072] After the green compact has been sintered, the RTB-based sintered magnet undergoes an aging treatment (aging treatment step (step S16)). Following the sintering step, the RTB-based sintered magnet is provided with an aging treatment step in which it is held at a temperature lower than that used during sintering. The aging treatment can be performed in two stages or in a single stage. In two-stage heating, the RTB-based sintered magnet is heated to 700°C or more and to 900°C or less for 1 to 3 hours, and then further heated to 500°C to 700°C for another 1 to 3 hours. In single-stage heating, the RTB-based sintered magnet is heated to approximately 600°C for 1 to 3 hours.The treatment conditions can be adjusted appropriately based on the number of aging treatments to be performed. Such an aging treatment can improve the magnetic properties of the RTB-based sintered magnet. Additionally, the aging treatment step (step S16) can be performed after a machining step (step S18) or a grain boundary diffusion step (step S19). [Cooling step: Step S17]

[0073] After the RTB-based sintered magnet has undergone an aging treatment, it is rapidly cooled in an Ar atmosphere (cooling step (step S17)). In this way, the RTB-based sintered magnet is obtained according to the present embodiment. The cooling rate is not particularly restricted and is preferably 30°C / min or more. [Processing step: Step S18]

[0074] The resulting RTB-based sintered magnet can be machined to achieve any desired shape (machining step: step S18). The machining process can involve, for example, shaping processes such as cutting, grinding, and the like, or bending processes such as drum polishing and the like. [Grain boundary diffusion step: Step S19]

[0075] A further step can be taken in which the heavy rare-earth element is diffused into a grain boundary of the machined RTB-based sintered magnet (grain boundary diffusion step: step S19). Grain boundary diffusion can be achieved by applying a composition containing the heavy rare-earth element to the surface of the RTB-based sintered magnet by coating, vapor deposition, or similar processes followed by heat treatment, or alternatively, by subjecting the RTB-based sintered magnet to heat treatment in an atmosphere containing the vapor of the heavy rare-earth element. This step can further improve the coercive field strength of the RTB-based sintered magnet. [Surface treatment step: Step S20]

[0076] Surface treatments such as platinizing, resin coating, oxidation treatment, chemical transformation treatment, and the like can be applied to the RTB-based sintered magnet obtained from the steps mentioned above (surface treatment step (step S20)). This further improves corrosion resistance.

[0077] Although the processing step (step S18), the grain boundary diffusion step (step S19) and the surface treatment step (step S20) have been carried out in the present embodiment, these steps do not necessarily have to be carried out.

[0078] The RTB-based sintered magnet according to the present embodiment is produced as described above, and its processing is completed. Additionally, a magnetic product can be obtained by magnetizing the resulting magnet.

[0079] In the RTB-based sintered magnet obtained in this manner according to the present embodiment, good magnetic properties are provided even if the carbon content is high, since the concentrated R-Ga-C region is contained in the grain boundary.

[0080] The RTB-based sintered magnet of the present embodiment can be used in a suitable manner, for example, as a magnet in a rotating machine with an external permanent magnet (SPM - surface permanent magnet) in which a magnet is attached to the surface of a rotor, in a rotating machine with an internal permanent magnet (IPM - interior permanent magnet) such as a brushless motor with an internal rotor, a permanent magnet reluctance motor (PRM) or the like.In particular, the RTB-based sintered magnet of the present embodiment can be used in a spindle motor for the rotary motion of a hard drive or in a voice coil motor in a hard drive drive, in a motor for an electric vehicle or for an electric hybrid car, in a motor for an electrically driven power steering system in a motor vehicle, in a servo motor for a machine tool, in a motor for a vibrator in a mobile phone, in a motor for a printer, as well as in a motor for a generator and the like. <Referenzbeispiele 1, 3 und 4, Beispiel 2>

[0081] First, raw material alloys were prepared using a strip casting process to produce sintered magnets with the magnet compositions A to D shown in Table 1. A first alloy, which mainly forms the main phase of the magnet, and a second alloy, which mainly forms the grain boundary, were prepared as raw material alloys, each having the compositions shown in Table 1. Additionally, the term "residual" used in Table 1 refers to the residual fraction of the respective alloy when the total composition is defined as 100 wt%, and (T.RE) refers to the total wt% occupied by all rare earth elements. [Table 1] Composition (mass %) mass ratio Relevant examples Relevant comparative examples Nd Pr Dy (T.RE) Ga Al Zr B Fe Composition A First alloy 20,00 10,50 0,00 30,50 0,00 0,10 0,60 0,94 rest 95 Reference example 1 Comparative example 1 and 5 to 8 Second alloy 33,00 17,00 0,00 50,00 6,00 0,00 0,00 0,00 rest 5 Composition specification of the sintered body 20,65 10,83 0,00 31,48 0,30 0,10 0,57 0, 89 rest Composition B First alloy 15,50 15,00 0,00 30,50 0,00 0,40 1,67 0,90 rest 90 Example 2 Comparative example 2 Second alloy 25,00 25,00 0,00 50,00 6,00 0,00 0,00 0,00 rest 10 Composition specification of the sintered body 16,45 16,00 0,00 32,45 0,60 0,36 1,50 0, 81 rest Composition C First alloy 30, 50 0,00 0,00 30, 50 0,00 0,50 0,90 0,92 rest 93 Reference example 3 Comparative example 3 Second alloy 50,00 0,00 0,00 50,00 6,00 0,00 0,00 0,00 rest 7 Composition specification of the sintered body 31,87 0,00 0,00 31,87 0,42 0,47 0,84 0,86 rest Composition D First alloy 30,00 0,00 0,50 30, 50 0,00 0,20 0,31 0, 98 rest 97 Reference example 4 Comparative example 4 Second alloy 50,00 0,00 0,00 50,00 6,00 0,00 0,00 0,00 rest 3 Composition specification of the sintered body 30,60 0,00 0,49 31,09 0, 18 0,19 0,30 0,95 rest

[0082] This was followed by hydrogen storage pulverization (i.e., coarse pulverization). Specifically, after hydrogen storage in the raw material alloy at room temperature, dehydration took place for 1 hour at 400°C in an argon atmosphere.

[0083] In the present examples and reference examples, each step from hydrogen storage pulverization to sintering (i.e., the fine pulverization and compression steps) was carried out in an Ar atmosphere with an oxygen concentration of less than 50 ppm (the same conditions were applied in the following examples, reference examples, and comparison examples).

[0084] Following hydrogen storage pulverization, but prior to fine pulverization, oleamide was added to the coarsely pulverized powder of each alloy at a rate of 0.4 wt% as a pulverizing aid. The resulting mixture was blended in a Nauta mixer. A jet mill was then used to perform the fine pulverization. During fine pulverization, the particle size of the finely pulverized powder was adjusted by modifying the classification conditions in the jet mill. The particle size obtained after pulverization is shown for each example in Table 2. [Table 2] composition Particle size after pulverization (µm) Holding step at 600°C Carbon content (mass %) Average size of the main phase grains (µm) Concentrated R-Ga-C area Magnetic properties HcJ difference to the comparison example (kA / m) Br(mT) HcJ(kA / m) Reference Example 1 Composition A 2,8 is 0,16 3, 4 available 1372 1602 35 Comparative example 1 2,8 none 0,16 3,4 none 1375 1567 Example 2 Composition B 1,6 is 0,30 1, 9 available 1352 1712 51 Comparative example 2 1,6 none 0,30 1, 9 none 1348 1661 Reference example 3 Composition C 2,2 is 0,21 2,8 available 1362 1646 59 Comparative example 3 2,2 none 0,21 2,8 none 1364 1587 Reference example 4 Composition D 3, 3 is 0,10 4, 0 available 1381 1542 26 Comparative example 4 3, 3 none 0,10 4, 0 none 1383 1516 Comparative example 5 Composition A 4, 5 is 0,07 5,3 none 1325 1387 -3 Comparative example 6 4, 5 none 0,07 5,3 none 1326 1390 Comparative example 7 Composition A + Carbon 2,8 is 0,35 3,5 available 1412 1142 5 Comparative example 8 2,8 none 0,35 3,5 none 1413 1137

[0085] The finely powdered first alloy and the finely powdered second alloy were then mixed using a Nauta mixer in the ratio shown in Table 1. This prepared a powder mixture that was used as the raw material powder for the RTB-based sintered magnet.

[0086] The resulting powder mixture was then filled into a mold located within an electromagnet, and the powder was compressed under a pressure of 120 MPa in a magnetic field of 1200 kA / m. A green compact was thus obtained.

[0087] The green compact was then sintered as follows. During sintering, the green compact was held in an argon atmosphere of 5 kPa, with the temperature increased to 600°C at a rate of 6°C / minute. The green compact was then held at 600°C in a vacuum for 2 hours. The temperature was then further increased. The green compact was held at 1030°C in a vacuum for 12 hours. The temperature was then rapidly cooled, resulting in a sintered body (the RTB-based sintered magnet). The sintered body then underwent a two-stage aging treatment: 1 hour at 850°C and 1 hour at 500°C (both in an argon atmosphere). This process yielded the RTB-based sintered magnets of Example 2 and Reference Examples 1, 3, and 4. (Comparative examples 1 to 4)

[0088] In comparison examples 1 to 4, RTB-based sintered magnets were produced, each corresponding to examples 1 to 4, except that the step in which the green body was left at 600°C for 2 hours was not additionally carried out during sintering. (Comparative examples 5 to 6)

[0089] An RTB-based sintered magnet of comparison example 5 was manufactured in a similar manner to example 1, except that alloys with composition A as shown in Table 1 were used and the particle size after pulverization was 4.5 µm or less. An RTB-based sintered magnet of comparison example 6 was manufactured as in example 5, except that the step of holding the green compact at 600°C for 2 hours was not additionally performed during sintering. (Comparative examples 7 to 8)

[0090] An RTB-based sintered magnet of comparison example 7 was produced as in example 1, except that granulated carbon black was added at a mass percentage of 0.2% during the mixing step to blend the first and second alloys. Additionally, an RTB-based sintered magnet of comparison example 8 was produced as in comparison example 7, except that the step of holding the green compact at 600°C for 2 hours during sintering was omitted. <auswertung>[Evaluation by structure]

[0091] In the RTB-based sintered magnet obtained in Example 2, Reference Examples 1, 3, and 4, and Comparison Examples 1 to 8, the surface of a cross-section was treated by ion thinning to eliminate the influence caused, for example, by oxidation of the outermost surface. The distribution of elements in the cross-section of the RTB-based sintered magnet was then examined and subsequently analyzed using ESMA (electron beam microanalysis). Specifically, each element, including Nd, Ga, and C, was analyzed and recorded in a 50 µm x 50 µm area, and then the region where the concentration distribution of each element, including Nd, Ga, and C, was higher than in the main phase grains was examined.

[0092] The results confirmed that in the RTB-based sintered magnets of Example 2, Reference Examples 1, 3, and 4, and Comparison Example 7, the region where the concentration distribution of each element, including Nd, Ga, and C, was higher than in the main phase grains (the concentrated R-Ga-C region) was present at the grain boundary. However, no concentrated R-Ga-C region was found at the grain boundary of the RTB-based sintered magnets of Comparison Examples 1 to 6 and Comparison Example 8.

[0093] Furthermore, in the RTB-based sintered magnets of Example 2 and Reference Examples 1, 3, and 4, where the concentrated R-Ga-C region was observed at the grain boundary, the concentrated R-Ga-C region (5 points) and the main phase crystal grain (1 point) were each subjected to quantitative analysis using ESMA. The result of Reference Example 1 is shown representatively in Table 3.

[0094] Furthermore, the composition ratio in this table refers to the ratio of each element when the total number of atoms of Nd, Pr, Dy, Fe, Ga, and C is defined as 100. In particular, the calculated composition ratio of C was influenced by the background during the ESMA measurement and tends to be higher than the actual value. However, the ratios of the values ​​to each other were not affected. [Table 3] Composition ratio (%) Nd+Pr+Dy Fe Ga C Reference Example 1 concentrated R-Ga-C area (average 5 points) 50 15 14 21 Main phase 12 76 0 12

[0095] As shown in Table 3, quantitative analysis using ESMA in Reference Example 1 also confirmed that the region where the concentration distribution of each element, including R (Nd+Pr+Dy), Ga, and C, was higher than in the main phase grains (the concentrated R-Ga-C region) is present at the grain boundary of the RTB-based sintered magnet. The concentrated R-Ga-C region with a similar composition was also found in the RTB-based sintered magnet of Example 2 and Reference Examples 3 and 4. [Analysis by composition]

[0096] The RTB-based sintered magnets obtained in Example 2, Reference Examples 1, 3, and 4, and Comparison Examples 1 to 8 were subjected to composition analysis using fluorescent X-ray spectroscopy combined with inductively coupled plasma mass spectrometry (ICP-MS). The results confirmed that the composition of each RTB-based sintered magnet was approximately equal to the composition of the added raw materials (composition specification of the sintered body as shown in Table 1). In addition, the carbon content was measured by combustion using an oxygen stream and infrared absorption. The results regarding the carbon content are summarized in Table 2. [Evaluation by grain size]

[0097] The average grain size of the main phase grains in the RTB-based magnets of Example 2, Reference Examples 1, 3, and 4, and Comparison Examples 1 to 8 was evaluated. To determine the average grain size of the main phase grains, a cross-section of a sample was milled and then examined under an optical microscope. This cross-section was then processed using image processing software to determine the grain size distribution. The average grain size of the main phase grains is summarized and shown in Table 2. [Magnetic properties]

[0098] The magnetic properties of the RTB-based sintered magnet of Example 2, Reference Examples 1, 3, and 4, and Comparison Examples 1 to 8 were determined using a BH tracer. The magnetic properties measured were the residual magnetic flux density Br and the coercive field strength HcJ. The results are summarized in Table 2.

[0099] As shown in Table 2, the RTB-based sintered magnets of Example 2 and Reference Examples 1, 3, and 4 had the same composition as their respective comparison examples 1 to 4, and the coercive field strength of the RTB-based sintered magnets of Example 2 and Reference Examples 1, 3, and 4 was 20 kA / m or more higher than that of the RTB-based sintered magnets of Comparison Examples 1 to 4. In other words, the RTB-based sintered magnets of Example 2 and the reference examples exhibited a higher coercive field strength. In the RTB-based sintered magnet of comparison examples 5 and 6, where the carbon content was less than 0.1 wt%, no concentrated R-Ga-C region was found, and a high coercive field strength was not obtained, even when the step of leaving the green body at 600°C for 2 hours was additionally carried out during sintering.In the RTB-based sintered magnets of comparison examples 7 and 8, where the carbon content was higher than 0.3 mass-%, a sufficient coercive field strength cannot be obtained due to the remarkably high carbon content. (Examples 5 and 8, reference examples 6 and 7)

[0100] In Examples 5 and 8 and Reference Examples 6 and 7, RT-β-based sintered magnets were produced as in Example 2 and Reference Examples 1, 3, and 4, except that the raw material alloys were prepared in a strip casting process to provide the sintered magnets with the compositions E to H shown in Table 4, and the particle size of the finely pulverized powder remained the same as shown in Table 5. Example 5 and Reference Example 6 are examples that contain Cu as a composition of the sintered magnet, and Reference Example 7 and Example 8 are examples that contain Cu and Co as a composition of the sintered magnet. [Table 4] Composition (mass %) Mass ratio is Relevant examples Relevant comparison examples Nd Pr Dy (T. RE) Ga Al Cu Co Zr B Fe Composition First alloy 24,00 7,50 0,00 31,50 0,53 0,10 0,00 0,00 1,00 0,79 rest 95 Example 1 5 Comparison example 9 Second alloy 38,00 12,00 0,00 50,00 10,00 0,00 12,00 0,00 0,00 0,00 rest 5 Composition specification of the sintered body 24,70 7,73 0,00 32,43 1,00 0,10 0,60 0,00 0,95 0,75 rest Composition F First alloy 29,00 0,00 0,00 29,00 0,00 0,65 0,00 0,00 0,22 0,97 rest 95 Reference example 6 Comparison example 10 Second alloy 50,00 0,00 0,00 50,00 4,00 0,00 6,00 0,00 0,00 0,00 rest 5 Composition specification of the sintered body 30,05 0,00 0,00 30,05 0,20 0,62 0,30 0,00 0,21 0, 92 rest Composition First alloy 30,00 0,00 0,00 30,00 0,00 0,20 0,00 0,26 0,60 0, 92 rest 95 Reference example 7 Comparison example 11 Second alloy 50,00 0,00 0,00 50,00 10,00 0,00 3,00 5,00 0, 00 0,00 rest 5 Composition specification of the sintered body 31,00 0,00 0,00 31,00 0,50 0,19 0,15 0,50 0,57 0,87 rest First alloy 31,00 0,00 0,00 31,00 0,00 0,20 0,00 0,50 0,40 0,88 rest 95 Composition Second alloy 30,00 0,00 20,00 50,00 12,00 0,00 5,00 20,00 0, 00 0,00 rest 5 Example 18 Comparison example 12 Composition specification of the sintered body 30,95 0,00 1,00 31,95 0,60 0,19 0,25 1,48 0,38 0,84 rest [Table 5] composition Particle size after pulverization (µm) Holding step at 600°C Carbon content (mass %) Average size of the main phase grains (µm) Concentrated R-Ga-C area Magnetic properties HcJ difference to the comparison example (kA / m) Br(mT) HcJ(kA / m) Example 5 Composition E 1, 7 is 0,25 2,1 available 1342 1795 89 Comparative example 9 1, 7 none 0,25 2,1 none 1344 1706 Reference Example 6 Composition F 3,0 is 0,12 3,6 available 1402 1452 94 Comparative example 10 3, 0 none 0,12 3,6 none 1407 1358 Reference example 7 Composition G 2,8 is 0,16 3, 4 available 1352 1656 114 Comparative example 11 2,8 none 0,16 3,4 none 1355 1542 Example 8 Composition H 2,5 is 0,18 3, 0 available 1324 1876 134 Comparative example 12 2,5 none 0,18 3,0 none 1326 1742 (Comparative examples 9 to 11)

[0101] In comparative examples 9 to 11, RTB-based sintered magnets were produced as in examples 5 and 8 and reference examples 6 and 7, with the exception that the step in which the green body was left at 600°C for 2 hours was not additionally carried out during sintering. <auswertung>

[0102] The RTB-based sintered magnets of Examples 5 and 8, Reference Examples 6 and 7, and Comparison Examples 9 to 11 were evaluated similarly to Example 2, Reference Examples 1, 3, and 4, and Comparison Examples 1 to 8. The results of the composition analysis confirmed that the composition of each of the RTB-based sintered magnets was approximately equal to the composition of the added raw materials (sintered body composition specification as shown in Table 4). Additionally, the carbon content and the average grain size of the main phase grains are shown in Table 5.

[0103] A structural analysis was performed similarly to that of Example 2 and Reference Examples 1, 3, and 4. The results confirmed that in the RTB-based sintered magnets of Examples 5 and 8 and Reference Examples 6 and 7, a region was present at the grain boundary where the concentration of each element, including Nd, Ga, and C, was higher than in the main phase grains. However, such a concentrated R-Ga-C region was not found at the grain boundary of the RTB-based sintered magnets of Comparison Examples 9 to 12.

[0104] In the RTB-based sintered magnet of Examples 5 and 8 and Reference Examples 6 and 7, where the concentrated R-Ga-C region was observed at the grain boundary, the concentrated R-Ga-C region (5 points) and the main phase (1 point) were each further subjected to quantitative analysis using ESMA. The results of Example 5 and Reference Example 7 are shown representatively in Table 6.

[0105] Furthermore, the composition ratio listed in Table 6 refers to the ratio of each element when the total number of atoms of Nd, Pr, Dy, Fe, Ga, Cu, and C is defined as 100. In particular, the calculated composition ratio of C was influenced by the background during the ESMA measurement and was therefore tended to be higher than the actual value. However, the ratios between the values ​​themselves were not affected. [Table 6] Composition ratio (%) Nd+Pr+Dy Fe Ga Cu Co C Example 5 Concentrated R-Ga-C area (average 5 points) 51 15 10 4 0 19 Main phase 12 77 1 0 0 10 Reference example 7 Concentrated R-Ga-C area (average 5 points) 48 11 11 4 4 22 Main phase 12 74 0 1 1 12

[0106] As shown in Table 6, quantitative analysis using ESMA in Example 5 and Reference Example 7 also confirmed that the region where the concentration distribution of each element, including R (Nd+Pr+Dy), Ga, and C, was higher than in the main phase grains (the concentrated R-Ga-C region) was present at the grain boundary of the RTB-based sintered magnet. Example 5 also confirmed that the concentrated R-Ga-C region contained Cu and that the concentration of Cu was higher than in the main phase grains. Furthermore, Reference Example 7 confirmed that the concentrated R-Ga-C region contained Co and Cu, and that the concentrations of Co and Cu were each higher than in the main phase grains.

[0107] It was confirmed that the concentrated R-Ga-C region with a similar composition to that in Example 5 was present in the RTB-based sintered magnet of Reference Example 6, and that the concentrated R-Ga-C region with a similar composition to that in Reference Example 7 was present in the RTB-based sintered magnet of Example 8.

[0108] The magnetic properties of the RTB-based sintered magnets of Examples 5 and 8, Reference Examples 6 and 7, and Comparison Examples 9 to 12 were determined using a BH tracer. The magnetic properties measured were the residual magnetic flux density Br and the coercive field strength HcJ. The results are summarized in Table 5.

[0109] As shown in Table 5, the coercive field strength of the RTB-based sintered magnet of Examples 5 and 8 and Reference Examples 6 and 7 was higher than that of the RTB-based sintered magnet of Comparison Examples 9 to 12, where the RT-β-based sintered magnet of Examples 5 and 8 and Reference Examples 6 and 7 had the same composition as Comparison Examples 9 to 12. The degree of improvement for HcJ in Example 5 and Reference Example 6 (which contain Cu in the concentrated R-Ga-C region) continued to tend to be higher compared to the Comparison Examples than for HcJ in Example 2 and Reference Examples 1, 3, and 4 (without Cu) compared to the Comparison Examples.It was also confirmed that the improvement level for HcJ in reference example 7 and example 8 (in which Cu and Co are contained in the concentrated R-Ga-C range) tended to be higher compared to the comparison examples than for HcJ in example 5 and reference example 6 (without Co) compared to the comparison examples. LIST OF REFERENCE MARKS 2 main phase grain 4 Two-Grain Border Phase 6 Triple point< / auswertung> < / auswertung>

Claims

[1] RTB-based sintered magnet comprising an RTB-based mixture as main phase grains, wherein R is at least one rare earth element, T is one or more elements from the iron group, including Fe or the combination of Fe and Co, the RT-β-based sintered magnet comprises 0.75 wt% to 0.84 wt% B, 0.1 wt% to 0.3 wt% C, 0.01 wt% to 0.2 wt% N, and a concentrated R-Ga-C region is present in the grain boundary formed between or under two or more adjacent main phase grains, and the concentrations of R, Ga and C in the concentrated R-Ga-C region are higher than those in the corresponding main phase grains. [2] The RT-β-based sintered magnet according to claim 1, wherein the concentrated R-Ga-C region further comprises Cu, and the concentration of Cu in the concentrated R-Ga-C region is higher than that in the main phase grains. [3] The RT-β-based sintered magnet according to claim 1 or 2, wherein the concentrated R-Ga-C region further comprises Co, and the concentration of Co in the concentrated R-Ga-C region is higher than that in the main phase grains.

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