Rare earth sintered magnets

Abstract

Provided is a rare earth sintered magnet comprising R (R is one or more rare earth elements, Nd being essential), T (T is one or more iron group elements, Fe being essential), B, M 1 (M 1 is one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi) and M 2 (M 2 is one or more elements selected from Ti, V, Zr, Nb, Hf, and Ta), with R2T 14 The rare earth sintered magnet with B phase as the main phase is characterized in that the M 1 0.5 to 2 atomic %, when the R, T, M 2 The atomic percentages of R, T, and M are [R], [T], [M ... 2 ], [B], the relationship (1) is satisfied: ([T] / 14)+[M 2 ]≤[B]≤([R] / 2)+([M 2 ] / 2), and 0.1 to 10 volume % of all grain boundary phases in the magnet are R6T 13 M 1 According to this rare earth sintered magnet, it is possible to obtain a rare earth sintered magnet having both high Br and high H cJ Excellent magnetic properties.

Description

Technical Field

[0001] The present invention relates to a method for producing a product having both high Br and high H cJ Rare earth sintered magnets with excellent magnetic properties. Background Art

[0002] As a functional material indispensable for energy conservation and enhanced functionality, the application and production volume of rare earth sintered magnets are expanding year by year. Among rare earth sintered magnets, Nd-based sintered magnets (hereinafter referred to as "Nd magnets") exhibit a particularly high residual magnetic flux density (Br). These magnets are used, for example, in drive motors for hybrid and electric vehicles, electric power steering motors, compressor motors for air conditioners, and voice coil motors (VCMs) for hard disk drives. Consequently, Nd magnets with high Br are used in motors for a variety of applications. For example, further miniaturization of motors requires even higher Br levels in Nd magnets.

[0003] On the other hand, at high temperatures, the coercive force (hereinafter referred to as “H cJ Therefore, in particular, rare earth sintered magnets for automotive use such as electric vehicle motors are required to have high H cJ .

[0004] In the past, in order to increase the H cJ Generally, heavy rare earth elements such as Dy and Tb are added. However, this is not necessarily a preferred method because its addition leads to a decrease in Br and its resources are rare and expensive.

[0005] In addition, as a way to increase the H cJ Other methods include the refinement of crystal particle size. This method mainly refines the crystal particle size after sintering by making the fine powder size during the fine grinding before molding finer. It is known that within a certain particle size range, as the particle size is refined, H cJ However, when the micronization is performed above a certain level, the concentration of impurities (mainly oxygen and nitrogen) in the fine powder increases due to the decrease in the crushing ability during fine grinding and the increase in the reactivity of the fine powder. cJ Reduced, or although H can be seen cJ However, it is difficult to increase H by the grain boundary diffusion method described later. cJ In order to improve this problem, a method of changing the pulverizing gas during fine pulverization to an inert gas such as He or Ar has been proposed (Patent Document 1).

[0006] Furthermore, H as Nd magnet cJIn addition to the method of increasing the concentration of heavy rare earth elements (Dy, Tb, etc.), a method of selectively gathering heavy rare earth elements (Dy, Tb, etc.) in the grain boundary phase in the Nd magnet (hereinafter referred to as "grain boundary diffusion method") is also known (Patent Document 2). This method is a method of attaching heavy rare earth element compounds such as Dy and Tb to the surface of the magnet by coating or other methods, and then performing a heat treatment at a high temperature. By forming a structure with a high concentration of Dy and Tb only in the area very close to the grain boundary of the main phase particles in the Nd magnet, a high H content can be obtained while suppressing the reduction of Br. cJ Increase the effect.

[0007] In addition, in recent years, as a way to improve H cJ The method proposed is to use R6Fe 13 Control of the grain boundary structure in the magnet with M phase (M is Si, Ga and other elements) (Patent Documents 3, 4). This is based on the fact that the magnet composition contains M elements such as Si and Ga, and only contains R2Fe as the main phase. 14 The stoichiometry of the X phase is the amount of X (X is B and C), so that R6Fe 13 The M phase precipitates at the grain boundary phase inside the magnet and continuously covers the main phase, making H cJ Method of enlargement.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2014 / 142137

[0011] Patent Document 2: International Publication No. 2006 / 044348

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2018-56188

[0013] Patent Document 4: International Publication No. 2013 / 191276 Summary of the Invention

[0014] Problems to be solved by the invention

[0015] However, the method proposed in Patent Document 1 to change the pulverizing gas during fine pulverization to an inert gas such as He or Ar is difficult to industrialize considering the price difference with nitrogen. In addition, as described in Patent Document 3, in order to achieve high H cJ , also proposed the R6Fe 13However, in this case, as described in Patent Document 4, the amount of X in the magnet is less than the stoichiometric amount and is insufficient, so R2Fe is present as the main phase of the Nd magnet. 14 The problem is that the amount of X phase formed is reduced and Br is reduced. Therefore, high Br and high H cJ There is a trade-off relationship, it is difficult to have both high Br and high H cJ .

[0016] The present invention has been made in view of the above problems, and its object is to achieve high Br and high H in the above Nd-based sintered magnet. cJ Taking both into account.

[0017] Means for solving problems

[0018] In order to achieve the above object, the present inventors have focused on the composition of Nd-based sintered magnets, especially the effect of B content and M elements such as Si and Ga on R6T 13 The relationship between the influence of the precipitation of M phase (T is an iron group element, with Fe as an essential element. M is an element such as Si or Ga) and the magnetic properties has been studied intensively. As a result, it was found that by adjusting the amount of these elements within an appropriate range, a sufficient amount of R2Fe 14 X phase (X is B and C) achieves high Br, and at the same time, a heavy rare earth concentrated phase based on the grain boundary diffusion method and the necessary minimum amount of R6T are analyzed at the grain boundary of the magnet structure. 13 M phase, achieving high H cJ , completed the present invention.

[0019] Therefore, the present invention provides the following rare earth sintered magnet.

[0020] [1] Rare earth sintered magnets contain R (R is one or more elements selected from rare earth elements, with Nd as an essential element), T (T is one or more elements selected from iron group elements, with Fe as an essential element), B, M 1 (M 1 is one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi) and M 2 (M 2 is one or more elements selected from Ti, V, Zr, Nb, Hf, and Ta), with R2T 14 The rare earth sintered magnet with B phase as the main phase is characterized by containing 0.5 to 2.0 atomic % of the M 1 , and in the R, T, M 2 The atomic percentages of R, T, and M are [R], [T], [M ... 2 ], [B], the following relational expression (1) is satisfied:

[0021] ([T] / 14)+[M 2 ]≤[B]≤([R] / 2)+([M 2 ] / 2)···(1)

[0022] Furthermore, 0.1 to 10 volume % of the total grain boundary phase in the magnet is R6T 13 M 1 Phase occupation.

[0023] [2] The rare earth sintered magnet of [1], wherein the content of R is 12.5 to 16.0 atomic %, the content of B is 5.5 to 8.0 atomic %, and the content of M is 1. 1 The content of M is 0.5 to 2.0 atomic %. 2 The content is 0.5 atomic % or less.

[0024] [3] The rare earth sintered magnet of [1] or [2], wherein the O content is 0.1 mass % or less, the N content is 0.05 mass % or less, and the C content is 0.07 mass % or less.

[0025] [4] The rare earth sintered magnet according to any one of [1] to [3], wherein the average crystal grain size is 4 μm or less.

[0026] [5] The rare earth sintered magnet according to any one of [1] to [4], characterized in that, within at least 500 μm from the surface of the rare earth sintered magnet, at least a portion near the surface of the main phase grain has a larger particle size than the center portion R of the main phase grain. 1 (R 1 It is an area with high concentration of one or more elements selected from rare earth elements and constitutes a part of the R).

[0027] [6] The rare earth sintered magnet according to any one of [1] to [5], wherein the R 1 At least a portion of is introduced into the sintered magnet by grain boundary diffusion.

[0028] Effects of the Invention

[0029] According to the rare earth sintered magnet of the present invention, the element composition, especially M 1 Element (M 1 The content of the R element (R is one or more elements selected from rare earth elements, with Nd as an essential element), the T element (T is one or more elements selected from the iron group elements, with Fe as an essential element), the M 1 Element (M 1is one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi), M 2 Element (M 2 By adjusting the relationship between the content of the element (one or more elements selected from Ti, V, Zr, Nb, Hf, and Ta) and B to a specific range and optimizing it, it is possible to obtain a high Br and high H cJ Excellent magnetic properties. DETAILED DESCRIPTION

[0030] The rare earth sintered magnet of the present invention comprises R (R is one or more elements selected from rare earth elements, with Nd as an essential element), T (T is one or more elements selected from iron group elements, with Fe as an essential element), B, M 1 (M 1 is one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi), M 2 (M 2 is one or more elements selected from Ti, V, Zr, Nb, Hf, and Ta).

[0031] As described above, R is one or more elements selected from rare earth elements, with Nd being an essential element. The R content is not particularly limited, but is preferably 12.5 atomic % or greater, more preferably 13.0 atomic % or greater, from the perspective of suppressing the crystallization of dissolved α-Fe in the alloy and promoting normal densification during sintering. Furthermore, from the perspective of achieving a high Br content, it is preferably 16.0 atomic % or less, more preferably 15.5 atomic % or less.

[0032] The proportion of Nd in R is not particularly limited, but is preferably 60 atomic % or more of all R elements, more preferably 75 atomic % or more. Furthermore, R elements other than Nd are not particularly limited, but may preferably contain Pr, Dy, Tb, Ho, Ce, Y, and the like.

[0033] The above-mentioned T is one or more elements selected from the iron group elements, namely, Fe, Co, and Ni, with Fe being an essential element. 1 、M 2 The remainder other than B is preferably 70 atomic % to 80 atomic %. The Fe content is preferably 70 atomic % to 85 atomic % of the entire rare earth magnet, more preferably 75 atomic % to 80 atomic %.

[0034] The amount of B is not particularly limited. However, from the perspective of sufficient formation of the main phase to ensure Br, the content is preferably 5.5 atomic % or more, more preferably 5.8 atomic % or more, and even more preferably 6.0 atomic % or more. Furthermore, considering the effect of the precipitation of Nd1Fe4X4 phase (X is B or B and C) on Br when the B content is too high, the content is preferably 8.0 atomic % or less, more preferably 7.0 atomic % or less, and even more preferably 6.5 atomic % or less.

[0035] As mentioned above, the above M 1 It is one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi, which form R6T 13 M 1 The optimal temperature range for heat treatment to ensure good productivity is obtained, thereby suppressing H cJ From the perspective of reducing 1 The content of M is 0.5 atomic % or more, preferably 0.8 atomic % or more, more preferably 1.0 atomic % or more. In addition, from the viewpoint of obtaining high Br, it is 2.0 atomic % or less, preferably 1.5 atomic % or less, more preferably 1.4 atomic % or less. That is, if M 1 If the amount is less than 0.5 atomic %, it is difficult to form a sufficient amount of R6T 13 M 1 Phase, unable to obtain sufficient H cJ On the other hand, if it exceeds 2.0 atomic %, the R2T of the main phase 14 The amount of B phase formed is reduced, so Br is reduced.

[0036] Here, in the rare earth sintered magnet of the present invention, the above-mentioned R6T 13 M 1 The phase is formed in the grain boundary phase, and 0.1 to 10 volume % of the total grain boundary phase in the magnet is covered by the R6T 13 M 1 The more preferred occupancy rate is 1.0 to 8.0% by volume. If the R6T 13 M 1 If the occupancy rate of the phase in the entire grain boundary phase is less than 0.1 volume %, sufficient H cJ On the other hand, if it exceeds 10% by volume, the main phase R2T 14 The amount of B phase formed is reduced, and Br is decreased. In either case, there is a possibility that the object of the present invention cannot be achieved.

[0037] R6T in the above grain boundary phase 13 M 1The volume ratio of the phase can be obtained, for example, as follows. First, the structure of the sintered magnet is observed by EPMA (electron beam microanalyzer), and the R6T is determined from the reflected electron composition imaging and semi-quantitative analysis results. 13 M 1 Phase, the R6T contained in all the grain boundary phases of the magnet is measured by image processing 13 M 1 The area ratio of the phase. This measurement can be performed at various locations on the sintered magnet, and the average value is defined as the volume ratio. The number of measurements can be, for example, the average of approximately 1,000 particles in images of 10 different locations.

[0038] As mentioned above, the above M 2 M is one or more elements selected from Ti, V, Zr, Nb, Hf, and Ta. From the viewpoint of obtaining the effect of suppressing abnormal grain growth of grains during sintering, the M is contained. 2 . 2 The content of M is not particularly limited, 2 Elements formed by M 2 -B phase makes R2T 14 From the viewpoint of reducing the ratio of the B phase and thereby reducing Br, it is preferably 0.5 atomic % or less, more preferably 0.3 atomic % or less, and even more preferably 0.2 atomic % or less.

[0039] Here, in the present invention, the above R, T, M 2 The contents of B and R are represented by [R], [T], [M ... 2 ] and [B], the adjustment is performed in a manner that satisfies the following relational expression (1).

[0040] ([T] / 14)+[M 2 ]≤[B]≤([R] / 2)+([M 2 ] / 2)···(1)

[0041] By satisfying this relationship, high Br and high H can be obtained. cJ The reason is not necessarily clear, but it can be speculated as follows. The above formula (1) shows that the amount of B contained is more than the stoichiometric amount. It is known that M such as Ti, Zr, and Nb 2 Elements generally form M with B 2 -B2 phase, the inventors conducted in-depth research and found that according to the fine structure of rare earth sintered magnets, unstable M 2 -B phase, taking this into consideration, by adding 2 The above formula (1) is derived by taking the amount of B required for the phase formation of the element. That is, if the B amount ratio is ([T] / 14)+[M 2] is less, then R2T as the main phase 14 The formation of the B phase is insufficient, so Br is reduced. In addition, if the B amount ratio is ([R] / 2)+([M 2 ] / 2) is too much, the formation of the R1T4B4 phase is excessive, and Br is also reduced, making it difficult to achieve the purpose of the present invention.

[0042] The rare earth sintered magnet of the present invention may contain O, N, and C in addition to the above-mentioned constituent elements. In this case, the O content is preferably 0.1% by mass or less, more preferably 0.08% by mass or less. In addition, the N content is preferably 0.05% by mass or less, more preferably 0.03% by mass or less. Furthermore, the C content is preferably 0.07% by mass or less, more preferably 0.05% by mass or less. When the C content exceeds 0.07% by mass, H cJ If the contents of O, N, and C are within the above ranges, good magnetic properties, especially good H cJ It should be noted that, in the present invention, the lower the content of O, N, and C, the better, but these elements are usually unavoidable elements that are difficult to completely eliminate.

[0043] Furthermore, the rare earth sintered magnet of the present invention may contain H, F, Mg, P, S, Cl, Ca, and other elements as unavoidable impurities in addition to the above-mentioned elements. In such cases, the total amount of these unavoidable impurities is allowed to be no more than 0.1% by mass relative to the total amount of the constituent elements and unavoidable impurities of the magnet, and the amount of these unavoidable impurities is preferably as small as possible.

[0044] In the rare earth sintered magnet of the present invention, although not particularly limited, it is preferred that the average crystal grain size be 4 μm or less, and more preferably 3.5 μm or less. By adjusting the average crystal grain size in this way, good magnetic properties, especially good H cJ . The determination of the average crystal grain size can be carried out, for example, by the following steps. First, after the cross section of the sintered magnet is polished to a mirror surface, the cross section of the grain boundary phase is selectively etched by immersing it in an etching solution such as Vilella etching solution (for example, a mixture with a mixing ratio of glycerol: nitric acid: hydrochloric acid = 3:1:2) using a laser microscope. Then, based on the obtained observation image, the cross-sectional area of ​​each particle is measured by image analysis, and the diameter of the equivalent circle is calculated. Then, based on the data of the area fraction occupied by each particle size, the average diameter is calculated. In addition, the average diameter is preferably the average of multiple particles in the images of multiple parts, for example, it can be set to the average of a total of about 2000 particles in the images of 20 different parts.

[0045] Next, a method for producing the rare earth sintered magnet of the present invention will be described.

[0046] The process for producing the rare earth sintered magnet of the present invention is basically the same as the conventional powder metallurgy method and is not particularly limited. It usually includes: a melting process of melting the raw materials to obtain a raw material alloy with a specified composition; a pulverizing process of pulverizing the raw material alloy to prepare alloy fine powder; a molding process of pressing the alloy fine powder into powder under the application of a magnetic field to obtain a molded body; and a heat treatment process of heat treating the molded body to obtain a sintered body.

[0047] First, in the melting process, the metal or alloy that becomes the raw material of each element is weighed in a manner to obtain a specified composition. After being weighed to the specified composition, the raw material is melted, for example, by high-frequency melting, and cooled to produce a raw material alloy. The raw material alloy is generally cast by a melting casting method or a thin strip continuous casting method in a flat mold or a book mold. In addition, the present invention can also be applied to the production of R2Fe2O3, which is close to the main phase of Nd magnets. 14 The so-called two-alloy method is a method in which an alloy composed of a B compound and an R-rich alloy that becomes a liquid phase auxiliary agent at the sintering temperature are coarsely crushed and then weighed and mixed. However, the alloy close to the main phase composition is easy to crystallize the α-Fe phase depending on the cooling rate and alloy composition during casting. Therefore, in order to homogenize the structure and eliminate the α-Fe phase, it is preferred to carry out a homogenization treatment at 700-1200°C for more than 1 hour in a vacuum or Ar atmosphere as needed. It should be noted that when an alloy close to the main phase composition is produced by a thin strip continuous casting method, homogenization can also be omitted. For the R-rich alloy that becomes a liquid phase auxiliary agent, in addition to the above-mentioned casting method, the so-called liquid rapid cooling method can also be applied.

[0048] The above-mentioned pulverization process can be, for example, a multi-stage process including a coarse pulverization process and a fine pulverization process. In the coarse pulverization process, for example, a jaw crusher, a Brownian mill, a pin mill or hydrogen pulverization can be used. In this case, in the present invention, there is no particular limitation, and from the viewpoint of achieving a reduction in the amount of O, N, and C and obtaining excellent magnetic properties, hydrogen pulverization is preferably used. In particular, in the case of an alloy produced by thin strip continuous casting, hydrogen pulverization is preferably applied, and a coarse powder of 0.05 mm to 3 mm, particularly 0.05 mm to 1.5 mm, can usually be obtained.

[0049] In the fine pulverization step, a method of pulverizing the coarse powder using a jet mill with a non-oxidizing gas flow such as N2, He, or Ar can be used. In the present invention, in the fine pulverization step, the coarse powder is finely pulverized to preferably 0.2 μm to 15 μm, more preferably 0.5 μm to 10 μm. O and N in the rare earth sintered magnet are mainly mixed in during the fine pulverization step. Therefore, in order to adjust the O and N contents in the rare earth sintered magnet, it is necessary to control the jet mill atmosphere. The O content in the rare earth sintered magnet is adjusted by controlling the O content and dew point in the jet mill atmosphere. The O content in the atmosphere during pulverization is preferably less than 1 ppm, and the dew point is preferably less than -60°C.

[0050] The nitrogen content in the rare earth sintered magnet can be adjusted by, for example, (A) fine pulverization using a jet mill with a He or Ar gas flow, (B) fine pulverization using a jet mill with an N2 gas flow, or (C) fine pulverization using a jet mill with an N2 gas flow using a coarse powder containing hydrogen. In these cases, in methods (B) or (C), the introduction of hydrogen or the use of a coarse powder containing hydrogen preferentially adsorbs hydrogen on the active surfaces generated by pulverization, hindering nitrogen adsorption and thereby reducing the nitrogen content in the rare earth sintered magnet.

[0051] Here, in one or both of the steps of coarse pulverization and fine pulverization of the raw material alloy, a lubricant composed of, for example, a saturated fatty acid or its ester may be appropriately added to improve the orientation of the powder during the subsequent step of forming in a magnetic field. In this case, increasing the amount of lubricant added is generally effective in improving the orientation. However, due to the carbon from the lubricant, a large amount of R-CON phase is formed in the rare earth sintered magnet, resulting in H cJ The difficulty of significantly reducing the orientation is therefore a problem. Therefore, when achieving improved orientation, it is preferable to increase the amount of lubricant in the fine powder obtained by finely pulverizing the coarse powder containing hydrogen using the method (C) above. It is believed that when the hydrogen contained in the rare earth sintered magnet produced from this fine powder is released during heat treatment, the lubricant chemically adsorbed on the surface of the fine powder is decomposed by this hydrogen through carbonyl reduction reactions, and further decomposed and dissociated into highly volatile lower alcohols through hydrogen-based cracking reactions. This action can reduce the carbon content remaining in the rare earth sintered magnet.

[0052] In the above molding process, a magnetic field of 400 to 1600 kA / m is applied to orient the alloy powder in the direction of the easy magnetization axis while compacting the powder using a compression molding machine. At this time, the density of the compact is preferably 2.8 to 4.2 g / cm 3 That is, from the perspective of ensuring the strength of the molded body and thus obtaining good operability, the density of the molded body is preferably 2.8 g / cm 3In addition, in order to improve the strength of the molded body after molding, a binder such as PVA or fatty acid may be added. On the other hand, from the perspective of obtaining a sufficient molded body strength while suppressing the disorder of the orientation of the particles during pressurization to obtain a preferred Br, the molded body density is preferably 4.2 g / cm 3 In order to suppress oxidation of the alloy fine powder, it is preferable to perform the molding in an inert gas atmosphere such as nitrogen or Ar.

[0053] In the above-mentioned heat treatment process, the molded body obtained in the molding process is sintered in a non-oxidizing atmosphere such as Ar gas or in a high vacuum. In the case of using a coarse powder containing hydrogen by the above-mentioned method (C), in order to suppress the temperature drop of the molded body accompanied by the release of hydrogen in the molded body (endothermic reaction) and the generation of cracks caused by the temperature difference, it is preferably kept at 200 to 600°C for 5 minutes to 10 hours, in a non-oxidizing atmosphere or a low vacuum atmosphere, and then sintered. Usually, the sintering is preferably carried out in a temperature range of 950°C to 1200°C for 0.5 to 10 hours. Next, in order to increase the H cJ The obtained sintered body may be subjected to heat treatment at a temperature lower than the sintering temperature. The heat treatment after sintering may be a two-stage heat treatment of high-temperature heat treatment and low-temperature heat treatment, or may be performed only at low-temperature heat treatment. In the high-temperature heat treatment, the sintered body is preferably heat treated at a temperature of 600 to 950°C, and in the low-temperature heat treatment, the sintered body is preferably heat treated at a temperature of 400 to 600°C.

[0054] The rare earth sintered magnet of the present invention can be obtained in this manner. As described above, the average grain size of the rare earth sintered magnet can be easily measured, for example, by observation using a laser microscope. Specifically, the average grain size can be determined by image analysis from the reflected electron image of the surface of the magnet after grinding or mirror finishing, etching the surface with an etching solution such as Nital or Vilella.

[0055] In addition, after the obtained rare earth sintered magnet is ground into a predetermined shape, a so-called grain boundary diffusion treatment may be performed, that is, the rare earth sintered magnet selected from R 2 Oxide, R 3 Fluoride, R 4 Fluoride oxide, R 5 The hydroxide, R 6 Carbonate, R 7 Alkaline carbonate, R 8 One or more of the elemental metals or alloys (R 2 ~R 8The diffusion source (one or more selected from rare earth elements) is heat-treated in a state of being present on the surface of the rare earth sintered magnet. The method for fixing the above-mentioned diffusion source to the magnet surface can adopt a dipping method, such as immersing the sintered magnet in a slurry containing powdered diffusion sources to coat the slurry and dry it, a screen printing method, or a dry film forming method such as sputtering or PLD. The temperature of the grain boundary diffusion heat treatment is a temperature lower than the sintering temperature, preferably above 700°C. From the viewpoint of obtaining a good structure and magnetic properties of the sintered magnet, there is no particular restriction on the time, preferably 5 minutes to 80 hours, more preferably 10 minutes to 50 hours. By this grain boundary diffusion treatment, the above-mentioned R contained in the powder is 2 ~R 8 Diffusion into the magnet enables H cJ It should be noted that, for the sake of convenience, the rare earth elements introduced by the grain boundary diffusion are referred to as R 2 ~R 8 , but after grain boundary diffusion, they are all included in the above-mentioned R component in the rare earth sintered magnet of the present invention. 2 ~R 8 The diffusion source is not particularly limited, but preferably a metal, compound or intermetallic compound containing one or more elements selected from Dy, Tb and Ho is used, thereby more effectively achieving H cJ increase.

[0056] The rare earth sintered magnet of the present invention only needs to satisfy the above element composition and the above relational expression (1). As the above R element, it is not necessary to include R introduced by the above grain boundary diffusion. 1 (R 1 R is introduced through the above-mentioned grain boundary diffusion process 2 ~R 8 elements), from obtaining better H CJ From the viewpoint of 1 In the magnet to which the grain boundary diffusion treatment is applied, the R element shows a characteristic concentration distribution. That is, within at least 500 μm from the magnet surface to which the diffusion source is applied, R is formed in at least a portion of the surface of the main phase grains. 1 The structure of the region where the concentration is higher than that of the center of the main phase grains.

[0057] Example

[0058] The present invention will be described in more detail below with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples.

[0059] [Examples 1, 2, Comparative Examples 1, 2]

[0060] Nd metal, Pr metal, Dy metal, ferroboron alloy, electrolytic Co, Al metal, Cu metal, Ga metal, Si metal, Zr metal and electrolytic iron (all metals have a purity of 99% or more) are weighed and mixed in a prescribed ratio, these raw materials are dissolved, and cast by a thin strip continuous casting method to obtain a raw material alloy in the form of flakes with a thickness of 0.2 to 0.4 mm. The obtained raw material alloy in the form of flakes is hydrogen embrittled in a hydrogen pressurized atmosphere to obtain a coarsely pulverized powder. Then, 0.20% by mass of stearic acid relative to 100% by mass of the coarsely pulverized powder is added and mixed as a lubricant to the obtained coarsely pulverized powder, and then dry-pulverized in a nitrogen stream using an airflow mill (jet mill device) to obtain a fine powder particle size (D 50 ) is 2.8 to 3.0 μm finely pulverized powder (alloy powder). 50 ) is the volume-based median particle size obtained by laser diffraction using the airflow dispersion method.

[0061] The finely pulverized powder is filled into a mold of a molding device in an inert gas atmosphere, oriented in a magnetic field of 15 kOe (1.19 MA / m), and simultaneously pressed in a direction perpendicular to the magnetic field. The density of the molded body at this time is 3.0 to 4.0 g / cm 3 The resulting compact was held at 600°C for 2 hours, then held in an Ar atmosphere and sintered in a vacuum at a temperature between 1040°C and 1080°C (a temperature at which densification due to sintering is fully achieved was selected for each sample) for 5 hours to obtain a Nd magnet raw material. The density of the obtained Nd magnet raw material was 7.5 g / cm 3 above.

[0062] For the obtained Nd magnet raw materials, high-frequency inductively coupled plasma emission spectrometry (ICP-OES) was used to analyze the metal components, and infrared absorption gas analysis was used to analyze oxygen, carbon, and nitrogen. The results are shown in Table 1. It should be noted that the values ​​recorded in Table 1 are atomic %. In addition, for each Nd magnet raw material, observation was performed using a laser microscope to measure the average crystal grain size. The results are shown in Table 2. Furthermore, the Nd magnet raw material was processed into a rectangular shape with a size of 15 mm × 7 mm × 12 mm to make a sample, and Br and H were measured using a BH tracer. cJ The results are shown in Table 2.

[0063] After processing the Nd magnet raw material into a rectangular shape with a size of 20mm×20mm×2.2mm, it is immersed in a slurry prepared by mixing 50% by mass of terbium oxide particles with an average particle size of 0.5μm with ethanol, and the slurry is applied and dried to form a terbium oxide coating on the surface of the Nd magnet raw material. Next, the Nd magnet raw material with the coating is heated at 950°C in a vacuum for 5 hours, and then subjected to a high-temperature heat treatment of cooling to 200°C at a cooling rate of 20°C / min to diffuse the terbium grain boundaries. Next, after heating at 450°C for 2 hours, a low-temperature heat treatment of cooling to 200°C at a cooling rate of 20°C / min is performed to obtain a Nd sintered magnet. The center portion of the obtained Nd sintered magnet is cut into a rectangular shape with a size of 6mm×6mm×2mm, and H is measured by a pulse tracer. cJ The results are shown in Table 2. In addition, the structure of the magnet piece was observed by EPMA, and R6T was determined from the reflected electron composition image and semi-quantitative analysis results. 13 M 1 Phase, the R6T contained in all the grain boundary phases of the magnet is measured by image processing 13 M 1 The results are shown in Table 2. In Table 2, items that satisfy the requirements of the present invention are indicated as o, and items that do not satisfy the requirements are indicated as x.

[0064] [Table 1]

[0065] Nd Pr Fe Co Cu Zr Al B Si Ga O N C Comparative Example 1 11.38 3.15 76.96 0.50 0.63 0.14 0.20 5.51 0.12 0.73 0.32 0.08 0.24 Comparative Example 2 11.38 3.16 76.91 0.49 0.62 0.14 0.20 5.62 0.12 0.73 0.28 0.09 0.27 Example 1 11.37 3.14 76.86 0.49 0.62 0.14 0.17 5.75 0.12 0.72 0.28 0.09 0.27 Example 2 11.36 3.15 76.71 0.49 0.62 0.14 0.20 5.84 0.12 0.73 0.29 0.09 0.25

[0066] (atom%)

[0067] [Table 2]

[0068]

[0069] [Examples 3 to 5, Comparative Examples 3 and 4]

[0070] The magnets were produced by the same procedure as in Example 1. At this time, as shown in Table 3, the Nd and Pr amounts were reduced compared to Example 1, the Fe amount was increased, and the B amount was changed as shown in Table 3 to produce magnets. The average crystal grain size, R6T 13 M 1 Phase occupancy, M 1 Content, Br, H cJ The results are shown in Table 4. In Table 4, items that satisfy the requirements of the present invention are indicated by o, and items that do not satisfy the requirements are indicated by x.

[0071] [Table 3]

[0072] Nd Pr Fe Co Cu Zr Al B Si Ga O N C Comparative Example 3 10.97 3.08 77.70 0.53 0.20 0.14 0.24 5.56 0.12 0.71 0.39 0.13 0.24 Comparative Example 4 10.71 3.11 77.95 0.50 0.19 0.15 0.24 5.68 0.14 0.72 0.32 0.10 0.21 Example 3 10.83 3.16 77.68 0.50 0.20 0.14 0.27 5.81 0.12 0.72 0.29 0.09 0.26 Example 4 10.87 3.10 77.72 0.50 0.20 0.15 0.17 5.90 0.12 0.72 0.32 0.09 0.25 Example 5 10.92 3.11 77.35 0.50 0.19 0.14 0.24 6.04 0.12 0.73 0.32 0.14 0.26

[0073] (atom%)

[0074] [Table 4]

[0075]

[0076] Comparing Examples 1 to 5 and Comparative Examples 1 to 4, it can be seen that when the M 1 On the basis of the content, when the conditions of formula (1) are further satisfied (Examples 1 to 5), high Br and high H cJ This is believed to be because by including more B than stoichiometric, R6T 13 M 1 The generation of the phase is minimized, thereby suppressing the decrease of Br and stably achieving high H cJ On the other hand, when the condition of formula (1) is not satisfied and B is less than the stoichiometric amount (Comparative Examples 1 to 4), it is found that although R6T 13 M 1 The formation of the phase enables high H cJ , but the main phase R2T 14 The amount of B phase decreases, and thus Br decreases significantly.

[0077] [Examples 6 to 9, Comparative Examples 5 and 6]

[0078] The magnets were prepared in the same manner as in Example 1. As shown in Table 5, the amount of Nd and Pr was reduced and the amount of Fe was increased compared to Example 1. The average grain size, R6T 13 M 1 Phase occupancy, M 1 Content, Br, H cJ The results are shown in Table 4. In Table 4, items that satisfy the requirements of the present invention are indicated by o, and items that do not satisfy the requirements are indicated by x.

[0079] [Table 5]

[0080] Nd Pr Fe Co Cu Zr Al B Si Ga O N C Comparative Example 5 11.03 2.93 78.31 0.49 0.18 0.14 0.24 5.91 0.02 0.00 0.35 0.08 0.31 Example 6 10.92 3.01 77.98 0.65 0.19 0.15 0.22 5.85 0.05 0.28 0.33 0.11 0.27 Example 7 10.91 3.03 77.92 0.54 0.18 0.14 0.22 5.85 0.02 0.46 0.34 0.11 0.27 Example 8 11.07 3.00 77.60 0.51 0.19 0.14 0.22 5.81 0.05 0.75 0.31 0.11 0.26 Example 9 11.17 3.04 77.08 0.52 0.19 0.14 0.22 5.82 0.05 1.13 0.30 0.11 0.23 Comparative Example 6 11.02 3.03 76.51 0.50 0.19 0.15 0.22 5.83 0.02 1.70 0.30 0.11 0.22

[0081] (atom%)

[0082] [Table 6]

[0083]

[0084] Comparing Examples 6 to 9 with Comparative Examples 5 and 6, it can be seen that 1 When the amount of the element is small (Comparative Example 5), R6T is not formed. 13 M1 Phase, can not get high H cJ On the other hand, in M 1 When the amount of the element is large (Comparative Example 6), R6T 13 M 1 The amount of phase formed increases, thereby reducing the amount of main phase and significantly reducing Br. 1 When both the contents are met, high Br and high H can be obtained as in Examples 6 to 9. cJ .

[0085] As described above, the magnets of Examples 1 to 9 satisfying the essential conditions of the present invention have H cJ With a Br value exceeding 27 kOe, it can be used in applications requiring high heat resistance, such as electric vehicles. Furthermore, a Br value exceeding 13.7 kG is achieved, enabling miniaturization of the motor.

Claims

1. Rare earth sintered magnets contain R, T, B, M 1 and M 2 , with R2T 14 Rare earth sintered magnets with B phase as the main phase, in, R is one or more elements selected from rare earth elements, with Nd being an essential element; T is one or more elements selected from the iron group, with Fe being an essential element; M 1 is one or more elements selected from the group consisting of Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi; M 2 is one or more elements selected from V, Zr, Nb, Hf, and Ta, It is characterized in that it contains 0.5 to 2.0 atomic % of the M 1 , and in the R, T, M 2 The atomic percentages of R, T, and M are [R], [T], [M ... 2 ], [B], the following relational expression (1) is satisfied: ([T] / 14)+[M 2 ]≤[B]≤([R] / 2)+([M 2 ] / 2)···(1), Furthermore, 0.1 to 10 volume % of the total grain boundary phase in the magnet is R6T 13 M 1 Phase occupied, The content of R is 12.5 to 16.0 atomic %, the content of B is 5.5 to 8.0 atomic %, and the content of M 1 The content of M is 0.5~2.0 atomic %. 2 The content is 0.5 atomic % or less.

2. The rare earth sintered magnet according to claim 1, wherein The O content is 0.1 mass % or less, the N content is 0.05 mass % or less, and the C content is 0.07 mass % or less.

3. The rare earth sintered magnet according to claim 1, wherein The average crystal grain size is 4 μm or less.

4. The rare earth sintered magnet according to claim 1, wherein Within at least 500 μm from the surface of the rare earth sintered magnet, at least a portion near the surface of the main phase grain has a larger R than that of the center of the main phase grain. 1 The concentration of high area, where R 1 It is one or more elements selected from rare earth elements, and constitutes at least a part of the R.

5. The rare earth sintered magnet according to claim 4, wherein The R 1 It is introduced into the sintered magnet through grain boundary diffusion.

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