R-t-b sintered magnet

Abstract

To provide an R-T-B sintered magnet having a high Br and a high HcJ, while reducing the usage of heavy rare earth elements.SOLUTION: An R-T-B sintered magnet includes: R in an amount of 26.5 mass% or more and 31.5 mass% or less (R is a rare earth element and includes at least one or two selected from the group consisting of Nd and Pr); M in an amount of 0.40 mass% or more and 1.50 mass% or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si and must include Cu); B in an amount of 0.85 mass% or more and 0.94 mass% or less; and T in an amount of 61.5 mass% or more (T is Fe and Co and 90% or more of T is Fe in terms of mass ratio), includes O in an amount of 0.05 mass% or more and 0.30 mass% or less, Tb in an amount of 0.20 mass% or more, and Dy in an amount of 0.30 mass% or less, and satisfies the following formula. Within a range from a surface to a depth of 200 μm, the concentration of the one or two selected from the group consisting of Nd and Pr and the concentration of Cu are gradually reduced in a depth direction from the surface. 26.0 mass%≤([Nd]+[Pr]+[Ce]+[La]+[Dy]+[Tb])-12([O]+[C])≤27.7 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an RTB-based sintered magnet. [Background technology]

[0002] RTB sintered magnets (where R is at least one rare earth element, T is Fe or Fe and Co, and B is boron) are known as the most highly efficient permanent magnets. For this reason, RTB sintered magnets are used in a variety of motors in fields including electric vehicles (EVs, HVs, and PHVs), renewable energy sources such as wind power generation, home appliances, and industrial applications. RTB sintered magnets are essential materials for making these motors smaller, lighter, more efficient, and more energy-efficient (improving energy efficiency). Furthermore, RTB sintered magnets are used in the drive motors of electric vehicles. The shift from internal combustion engines to electric vehicles contributes to the prevention of global warming by reducing greenhouse gas emissions such as carbon dioxide (fuel and exhaust emissions). In this way, RTB sintered magnets are making a significant contribution to the realization of a clean energy society.

[0003] RTB sintered magnets are mainly R2T 14 It is composed of crystal grains made of B-type compounds and a grain boundary phase located at the grain boundaries of these crystal grains (for example, Patent Document 1). 14 B main phase grain and two adjacent R2T 14 The present invention discloses a rare earth sintered magnet characterized in that it comprises a two-particle grain boundary phase between B main phase crystal grains, the thickness of the two-particle grain boundary phase being 5 nm or more and 500 nm or less, and the phase having a magnetic property different from that of the ferromagnetic material. R2T that constitutes the grains 14 B-type compounds are ferromagnetic materials with high saturation magnetization and anisotropic magnetic field, and they determine the properties of RTB-based sintered magnets.

[0004] RTB sintered magnets have a coercive force H cJ (Hereafter, simply "H cJTherefore, the RTB-based sintered magnets used in electric vehicle motors in particular require high H cJ i.e., higher H at room temperature cJ It is required to have the following. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2014-209546 Summary of the Invention [Problem to be solved by the invention]

[0006] R2T 14 When light rare earth elements RL (mainly Nd, Pr) in B-type compounds are replaced by heavy rare earth elements RH (mainly Tb, Dy), H cJ However, H cJ While R2T 14 The saturation magnetization of the B-type compound phase decreases, resulting in a remanent magnetic flux density B r (Hereafter, simply "B r ") decreases. In particular, Tb has problems such as unstable supply and price fluctuations due to the fact that the amount of Tb is originally small and the production areas are limited. Therefore, it is recommended to use as little Tb as possible (use as little as possible) and to use B r While suppressing the decline of cJ It is required to obtain

[0007] The rare earth sintered magnet disclosed in Patent Document 1 has a high H content at high temperatures while reducing the amount of heavy rare earth elements RH such as Tb. cJ However, compared to sintered magnets containing heavy rare earth elements RH, the magnetic properties (B r and H cJ ) is inferior. In recent years, especially in electric vehicle motors, r and HcJ Further improvement is required.

[0008] Therefore, one embodiment of the present invention is to reduce the amount of heavy rare earth elements RH such as Tb while increasing the amount of B r and H cJ The object of the present invention is to provide an RTB based sintered magnet that can further improve the above. [Means for solving the problem]

[0009] Aspect 1 of the present invention is R: 26.5 mass% or more and 31.5 mass% or less (R is a rare earth element, including one or two elements selected from the group consisting of Nd and Pr), M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu), B: 0.85% by mass or more and 0.94% by mass or less, and T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe by mass ratio), O: 0.05% by mass or more and 0.30% by mass or less, Tb: 0.20% by mass or less, and Dy: 0.30% by mass or less, and satisfies the following formula (1): In the RTB sintered magnet, the concentration of one or two elements selected from the group consisting of Nd and Pr and the concentration of Cu gradually decrease from the surface to a depth of 200 μm. 26.0 mass%≦([Nd]+[Pr]+[Ce]+[La]+[Dy]+[Tb])-12([O]+[C])≦27.7 mass% (1) Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O] and [C] are the contents of Nd, Pr, Ce, La, Dy, Tb, O and C, respectively, expressed in mass%.

[0010] Aspect 2 of the present invention is The RTB based sintered magnet according to aspect 1 necessarily contains Ga as M, the Ga content is at least 0.3 mass %, and the Ga concentration does not decrease gradually from the surface to a depth of 200 μm. [Effects of the Invention]

[0011] According to an embodiment of the present invention, the amount of heavy rare earth element RH such as Tb is reduced while B r and H cJ It is therefore possible to provide an RTB sintered magnet with further improved properties. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flowchart showing an example of steps in a method for producing an RTB based sintered magnet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The inventors have been working on the development of RTB sintered magnets that can improve magnetic properties (especially B r and H cJ We have conducted extensive research to improve the R2T 14 It was found that when the "low boron" composition of the B compound is lower than the stoichiometric composition, the effect of improving the magnetic properties due to the grain boundary diffusion of the rare earth element R and the metal element M is enhanced. 14 It was found that the same effect can be obtained even if part of the B in the B compound is replaced by carbon (C). 14 It was found that the C that replaced the B in the B compound bonded with the rare earth oxides in the grain boundaries during the sintering process, forming rare earth oxygen carbon compounds (ROC compounds) in the grain boundaries. It was also found that the atomic ratio in this case was R:(C,O) = 1:1. When such ROC compounds were formed in the grain boundaries, the R2T, which is the main phase, was formed. 14 The content of C that constitutes the B compound decreases. As mentioned above, R2T 14Even if a part of B in the B compound is substituted by C, the effect of "low boron" can be obtained. Therefore, the main phase is R2T 14 By reducing the content of C constituting the B compound, the total amount of B and C is effectively reduced. Also, the formation of R-O-C compounds at the grain boundaries means that a part of the rare earth element R contained in the raw material alloy is consumed in the formation of the R-O-C compounds. Note that the R-O-C compounds (rare earth oxycarbides) include R-O compounds (rare earth oxides) and R-C compounds (rare earth carbides).

[0014] From the above, the inventor considered that when diffusing the rare earth element R or the metal element M from the surface to the inside of the low-boron R-T-B sintered body, in order to optimize the effect of improving the magnetic properties by diffusion, it is necessary to control the thickness and structure of the grain boundaries, and for that purpose, it is necessary to satisfy an appropriate relationship among the contents of R, O, and C. Furthermore, R controlled to have an appropriate content was assumed to enhance the effect of improving the magnetic properties by grain boundary diffusion of R and M in the low-boron composition R-T-B sintered magnet. As a result of investigations based on these findings, by introducing R (Nd and Pr) and Cu by diffusion from the magnet surface into an R-T-B sintered magnet having a specific component composition that satisfies the following formula (1) and controls the content of B and the content of M (Ga, Cu, Zn, Al, and Si) to appropriate amounts, an R-T-B sintered magnet having excellent magnetic properties was obtained, and the invention according to the embodiment of the present application was completed. <No.

[0015] <No. Hereinafter, the R sintered magnet according to the embodiment (hereinafter sometimes simply referred to as "sintered magnet") will be described in detail.

[0016] <R-T-B Sintered Magnet> The R-T-B sintered magnet is R: 26.5 mass% or more and 31.5 mass% or less (R is a rare earth element and includes one or two selected from the group consisting of Nd and Pr), M: 0.40 mass% or more and 1.50 mass% or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si and necessarily includes Cu), B: 0.85% by mass or more and 0.94% by mass or less, and T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe by mass ratio), O: 0.05% by mass or more and 0.30% by mass or less, Tb: 0.20% by mass or less, and Dy: 0.30 mass % or less.

[0017] It is desirable that the content of heavy rare earth elements RH (especially Tb and Dy) contained in the sintered magnet be lower than in the past. The sintered magnet does not necessarily have to contain RH. In other words, the lower limit of the RH content in the sintered magnet is 0 mass%. The Tb content is preferably limited to 0.10 mass % or less. The Dy content is preferably limited to 0.20 mass % or less.

[0018] A sintered magnet satisfies the following formula (1): 26.0 mass%≦([Nd]+[Pr]+[Ce]+[La]+[Dy]+[Tb])-12([O]+[C])≦27.7 mass% (1) Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O], and [C] are the contents, expressed in mass%, of Nd, Pr, Ce, La, Dy, Tb, O, and C, respectively. If the sintered magnet does not contain one or more of Nd, Pr, Ce, La, Dy, Tb, O, and C, the content of the element not contained is considered to be "0 mass%" and is substituted into formula (1).

[0019] By adjusting the contents of R (particularly Nd, Pr, Ce, La, Dy, and Tb), O, and C in the sintered magnet so as to satisfy the above formula (1), a high B r and H cJThe carbon (C) content in the sintered magnet is preferably 0.05% by mass or more and 0.18% by mass or less. The carbon content can be adjusted by the amount of lubricant added during pulverization and molding. Preferably, the content of formula (1) is 26.0 mass % or more and 27.5 mass % or less, more preferably 26.3 mass % or more and 27.4 mass % or less, and particularly preferably 27.0 mass % or more and 27.4 mass % or less. r and H cJ can be obtained.

[0020] The composition of each component of the sintered magnet will now be described in detail.

[0021] (R: 26.5% by mass or more and 31.5% by mass or less) R is a rare earth element, and includes one or two elements selected from the group consisting of Nd and Pr. The R content is 26.5 mass% or more and 31.5 mass% or less. If the R content is less than 26.5 mass%, it may be difficult to densify during sintering, and if it exceeds 31.5 mass%, the main phase ratio decreases and B r The content of R is preferably 26.8 mass % or more and 30.0 mass % or less. When R is in this range, a higher B r can be obtained.

[0022] (M: 0.40 mass% or more and 1.50 mass% or less) M is at least one element selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu. The content of M (the total content of Ga, Cu, Zn, Al, and Si) is 0.40 mass% or more and 1.50 mass% or less. When M is in this range, high H cJ can be achieved. The sintered magnet always contains Cu as M, but preferably also contains Ga. cJ can be further improved.

[0023] Furthermore, as a result of further investigations, the inventors have found that compared to a sintered magnet produced by diffusing one or two elements selected from the group consisting of Nd and Pr, Cu, and a portion or all of Ga in a diffusion step, a sintered body containing 0.3 mass% or more of Ga, in which all of the Ga is derived from the raw materials (i.e., contained in the sintered magnet alloy), and then diffusing one or two elements selected from the group consisting of Nd and Pr, and Cu, can produce a significantly higher H cJ We have newly discovered that this can be achieved. That is, the sintered magnet of the present disclosure must contain Cu and Ga as M, and the Ga content is preferably 0.3 mass% or more, and the Ga concentration does not gradually decrease from the surface toward the depth within a range from the surface to a depth of 200 μm. The fact that the Ga concentration does not gradually decrease from the surface toward the depth indicates that a step of diffusing Ga from the magnet surface toward the interior of the magnet has not been carried out using a diffusion source containing Ga.

[0024] As described above, Cu is preferably derived from Cu diffused from the surface of the sintered body in the diffusion step carried out after the sintering step. cJ The entire amount of Cu contained in the sintered magnet may be derived from diffusion, or a portion of the Cu may be derived from the raw materials.

[0025] The preferred contents of Ga, Cu, Zn, Al and Si are as follows: Ga: more than 0.3% by mass and not more than 0.80% by mass, Cu: more than 0.1% by mass and 0.70% by mass or less, Zn: 0% by mass or more and 0.2% by mass or less, Al: 0% by mass or more and 0.8% by mass or less, and Si: 0 mass% or more and 0.2 mass% or less.

[0026] (B: 0.85 mass% or more and 0.94 mass% or less) The B content is 0.85% by mass or more and 0.94% by mass or less. By including B within the range of the present disclosure in the sintered magnet, high H cJThe content is preferably 0.85% by mass or more and 0.90% by mass or less, more preferably 0.87% by mass or more and 0.88% by mass or less, and H cJ can be further improved.

[0027] (O: 0.05 mass% or more and 0.30 mass% or less) The O content is 0.05% by mass or more and 0.30% by mass or less. When the sintered magnet contains O within the range of the present disclosure, it can have a high H cJ can be achieved.

[0028] (Tb: 0.20% by mass or less) The Tb content is 0.20% by mass or less, and preferably 0.10% by mass or less. By including Tb, the H content of the sintered magnet is improved. cj However, if it is contained in excess, B r Since Tb resources are scarce and the production areas are limited, it is desirable to reduce the amount used as much as possible, and it is preferable that Tb is not contained (that is, the Tb content is 0 mass %).

[0029] (Dy: 0.30 mass% or less) The Dy content is 0.30% by mass or less, and preferably 0.20% by mass or less. Dy may not be contained (i.e., the Dy content may be 0% by mass). Like Tb, the inclusion of Dy contributes to the improvement of the H content of the sintered magnet. cj However, if it is contained in excess, B r decreases.

[0030] (T: 61.5% by mass or more) T is Fe and Co, and 90% or more of T is Fe in terms of mass ratio. The sintered magnet contains 61.5 mass % or more of T, and B r This can improve the magnet's magnetic properties. It is particularly preferable that the balance in the component composition of the sintered magnet is T and unavoidable impurities. For example, in the case of a sintered magnet that contains R, M, B, O, and C but does not contain Tb, Dy, or any of the optional additional elements described below, it is preferable that the balance of R, M, B, O, and C is T and unavoidable impurities. Co may be contained as part of T, which can improve corrosion resistance. However, if the ratio of the Co content to the T content exceeds 10%, high B r may not be obtained.

[0031] Sintered magnets may contain unavoidable impurities such as Cr, Mn, La, Ce, Sm, Ca, and Mg that are typically contained in didymium alloys (Nd-Pr), electrolytic iron, and ferroboron. Furthermore, unavoidable impurities contained during the manufacturing process include N (nitrogen). The sintered magnet according to the embodiment may also contain one or more other elements (optional additional elements). For example, small amounts (about 0.1% by mass each) of such elements as Ag, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, Pb, and Bi may be contained. The total amount of such elements may be, for example, about 1.0% by mass. This amount allows for high H cJ It is therefore quite possible to obtain an RTB based sintered magnet having the above properties.

[0032] In the sintered magnet of this embodiment, the concentration of one or two elements selected from the group consisting of Nd and Pr gradually decreases from the surface to a depth of 200 μm. In addition, the concentration of Cu also gradually decreases from the surface to a depth of 200 μm. A sintered magnet with such a concentration distribution can be obtained by carrying out a process of diffusing one or two elements selected from the group consisting of Nd and Pr and Cu from the magnet surface to the magnet's interior during production. By carrying out a diffusion process during the production of a sintered magnet, the magnetic properties of the resulting sintered magnet can be improved. It is preferable that the Ga concentration does not decrease gradually from the surface to a depth of 200 μm, that is, it is preferable that a step of diffusing using a diffusion source containing Ga is not carried out.

[0033] The concentrations of Nd, Pr, and Cu in the range from the surface to a depth of 200 μm can be confirmed by performing line analysis (line scan analysis) on the cross-section of the sintered magnet in the range from the magnet surface to near the magnet center up to a depth of 200 μm by means of energy dispersive X-ray spectroscopy (EDX). It is preferable to measure on a cross-section perpendicular to the surface and more than 200 μm away from the end of the surface. When performing line analysis, the measurement is carried out in a direction orthogonal to the surface (the outer periphery of the measurement cross-section) within a region more than 200 μm away from the end of the measurement cross-section so as not to measure the range within 200 μm from the outer periphery of the measurement cross-section. The concentration of Ga can also be confirmed by performing the measurement in the same manner.

[0034] <Manufacturing method of R-T-B sintered magnet> Hereinafter, embodiments of the manufacturing method of the R-T-B sintered magnet of the present disclosure will be described.

[0035] As shown in FIG. 1, the manufacturing method in the present embodiment may include a step S10 of preparing an R-T-B sintered body, a step S20 of preparing an R1-M alloy, a step S30 of performing a first heat treatment, and a step S40 of performing a second heat treatment. Step S30 is a step (diffusion step) of diffusing R1 and M into the magnet interior by bringing at least a part of the R1-M alloy into contact with at least a part of the surface of the R-T-B sintered body and performing the first heat treatment at a temperature of 700°C or higher and 950°C or lower in a vacuum or inert gas atmosphere. Step S40 is a step of performing a second heat treatment on the R-T-B sintered magnet on which the first heat treatment has been performed at a temperature of 400°C or higher and 750°C or lower and at a temperature lower than the first heat treatment temperature in a vacuum or inert gas atmosphere. Hereinafter, each of these steps will be described in more detail.

[0036] (Step of preparing R-T-B sintered body) First, the composition of the R-T-B sintered body (hereinafter sometimes simply referred to as "sintered body") will be described.

[0037] One of the distinctive features of the sintered body used in this embodiment is that the R, oxygen, carbon, and other contents of the sintered body are adjusted to ultimately produce a sintered magnet that satisfies the above-mentioned formula (1). Therefore, it is preferable to prepare a sintered body that satisfies the following relationships: 0.85% by mass≦[B]≦0.94% by mass, 25.8% by mass≦([Nd]+[Pr]+[Ce]+[La]+[Dy]+[Tb]−12([O]+[C])≦27.5% by mass, and 0.05% by mass≦[O]≦0.30% by mass. By subjecting such a sintered body to a diffusion process (described later), it is possible to prevent excessive diffusion of R, M, and other elements within the sintered body and significantly promote grain boundary diffusion.

[0038] The sintered body prepared in this step has, for example, the following composition. R: 26.3 mass% or more and 31.3 mass% or less (R is a rare earth element and includes one or two elements selected from the group consisting of Nd and Pr), B: 0.85% by mass or more and 0.94% by mass or less, T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe by mass ratio), M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu); Tb: 0.20% by mass or less, and Dy: 0.30 mass% or less. Preferably, the balance consists of T and unavoidable impurities.

[0039] Next, a method for preparing the sintered body will be described.

[0040] First, an alloy for an RTB based sintered magnet (hereinafter sometimes simply referred to as "alloy for a sintered magnet") is prepared, and then this alloy is roughly crushed by, for example, a hydrogen crushing method.

[0041] Examples of methods for producing alloys for sintered magnets are given below. An alloy ingot can be obtained by ingot casting, in which a metal or alloy previously prepared to have the above-described composition is melted and poured into a mold to solidify. Alternatively, the alloy can be produced by strip casting, in which a molten metal or alloy previously prepared to have the above-described composition is brought into contact with a single roll, twin rolls, rotating disk, or rotating cylindrical mold, where it is rapidly cooled to produce a rapidly solidified alloy. Alternatively, flake-shaped alloys can be produced by other rapid-cooling methods, such as centrifugal casting.

[0042] In embodiments of the present invention, alloys produced by either the ingot method or the quenching method can be used. However, alloys produced by a quenching method such as strip casting are preferred. The thickness of alloys produced by the quenching method is typically in the range of 0.03 mm to 1 mm and in the form of flakes. The molten alloy begins to solidify at the surface where it contacts the chill roll (the roll contact surface), and crystals grow columnarly from the roll contact surface in the thickness direction. Compared to alloys (ingot alloys) produced by conventional ingot casting (mold casting), quenched alloys are cooled in a shorter time, resulting in a finer structure and smaller crystal grain size. Furthermore, the grain boundary area is larger. Because the R-rich phase spreads widely within the grain boundaries, the quenching method provides excellent dispersibility of the R-rich phase. Therefore, hydrogen pulverization easily causes fracture at the grain boundaries. By hydrogen pulverizing the quenched alloy, the size of the hydrogen pulverized powder (coarsely pulverized powder) can be reduced to, for example, 1.0 mm or less. The coarsely pulverized powder obtained in this manner is then pulverized, for example, using a jet mill.

[0043] In this embodiment, the pulverization conditions are adjusted so that the oxygen content of the final sintered magnet falls within a specific range (0.05% by mass or more and 0.30% by mass or less). Jet mill pulverization is performed in an inert atmosphere such as nitrogen. Pulverization may also be performed in a humidified atmosphere, for example. Preferably, the powder particles are made small (average particle size d50 is 2.0 μm or more and 10.0 μm or less, more preferably 2.0 μm or more and 8.0 μm or less, even more preferably 2.0 μm or more and 4.5 μm or less, and even more preferably 2.0 μm or more and 3.5 μm or less). By making the powder particles small, high H cJ can be obtained.

[0044] The average particle size (d50) can be measured by an air dispersion laser diffraction method (in accordance with JIS Z 8825: revised edition, 2013). That is, in this specification, the average particle size means the particle size (median diameter) at which the cumulative particle size distribution (volume basis) from the small particle size side is 50%.

[0045] As long as the fine powder used to prepare the sintered body satisfies the above-mentioned conditions, it may be prepared from one type of raw material alloy (single raw material alloy), or may be prepared by using two or more types of raw material alloys and mixing them (blending method).

[0046] In a preferred embodiment, a powder compact is produced from the above fine powder by pressing in a magnetic field, and then this powder compact is sintered to obtain an RTB-based sintered body.

[0047] To prevent oxidation during magnetic field pressing, it is preferable to form powder compacts by pressing in an inert gas atmosphere or wet pressing. In particular, with wet pressing, the surfaces of the particles that make up the powder compact are coated with a dispersant such as an oil, preventing contact with oxygen or water vapor in the atmosphere. This prevents or minimizes oxidation of the particles by the atmosphere before, during, or after the pressing process. This makes it easier to control the oxygen content of the sintered magnet within a specified range. When performing magnetic field wet pressing, a slurry is prepared by mixing fine powder with a dispersant, which is then supplied to the cavity of a mold in a wet pressing device and press-molded in a magnetic field.

[0048] The powder compact is preferably sintered at a temperature in the range of 950°C to 1150°C. To prevent oxidation during sintering, residual gas in the atmosphere may be replaced with an inert gas such as helium or argon. The resulting sintered compact may be subjected to a heat treatment. Known conditions for the heat treatment, such as the heat treatment temperature and time, may be used.

[0049] The sintered body may be prepared by a known method, such as the PLP (Press-Less Process) method described in JP-A-2006-19521, without being subjected to molding or the like.

[0050] (R1-M alloy preparation process) In this embodiment, R1 and M are diffused from the surface to the interior of the sintered body. For this purpose, an alloy containing these target elements for diffusion (referred to as an "R1-M alloy") is prepared.

[0051] First, the composition of the R1-M alloy will be described. R1 in the R1-M alloy is a rare earth element, and is one or two elements selected from the group consisting of Nd and Pr. The R1 content is preferably 65% ​​to 95% by mass, and more preferably 70% to 95% by mass, of the entire R1-M alloy. M in the R1-M alloy is at least one element selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu. In a preferred embodiment, M is at least one element selected from the group consisting of Cu, Zn, and Si, and must contain Cu. The M content is preferably 5% to 35% by mass, and more preferably 5% to 30% by mass, of the entire R1-M alloy.

[0052] The shape and size of the R1-M alloy are not particularly limited and can be any shape, such as a film, foil, powder, block, or particle.

[0053] Next, the method for producing the R1-M alloy will be explained.

[0054] The R1-M alloy can be prepared by a raw material alloy production method commonly used in the manufacture of sintered magnets, such as die casting, strip casting, single-roll rapid cooling (melt spinning), atomization, etc. Alternatively, the R1-M alloy may be prepared by pulverizing the alloy obtained by the above method using a known pulverizing means such as a pin mill.

[0055] (Step of carrying out first heat treatment (diffusion step)) At least a portion of the surface of the sintered body prepared by the above method is brought into contact with at least a portion of an R1-M alloy, and a first heat treatment is carried out in a vacuum or inert gas atmosphere at a temperature of 700°C to 950°C (first heat treatment temperature). The first heat treatment is a process for diffusing R1 and M into the interior of the sintered body (i.e., a diffusion process), and the heat treatment produces a liquid phase containing R1 and M from the R1-M alloy, and the elements that form this liquid phase diffuse from the surface of the sintered body into the interior of the sintered body via the grain boundaries in the sintered body.

[0056] If the first heat treatment temperature is less than 700°C, the amount of liquid phase containing R1 and M is too small, resulting in a high H cJ On the other hand, when the temperature exceeds 950°C, H cJ The first heat treatment temperature is preferably 850°C or higher and 950°C or lower, and the higher H cJ Preferably, the sintered body subjected to the first heat treatment (700°C or higher and 950°C or lower) is cooled from the first heat treatment temperature to 300°C at a cooling rate of 5°C / min or higher, and a higher H cJ More preferably, the cooling rate is 15°C / min or more.

[0057] The first heat treatment can be performed by placing an R1-M alloy of any shape on the surface of the sintered compact and using a known heat treatment device. For example, the surface of the sintered compact can be covered with a powder layer of R1-M alloy and then the first heat treatment can be performed. For example, a slurry containing the R1-M alloy dispersed in a dispersing medium can be applied to the surface of the sintered compact, and the dispersing medium can be evaporated to bring the R1-M alloy layer into contact with the sintered compact, and then the first heat treatment can be performed. Examples of dispersing mediums include alcohols (e.g., ethanol), aldehydes, and ketones. Alternatively, an R1-M alloy film can be formed on the surface of the sintered compact using a known sputtering device, and then the first heat treatment can be performed. Furthermore, when introducing a heavy rare earth element RH into the sintered compact, not only can an R1-M alloy containing RH be used, but also a fluoride, oxide, or oxyfluoride of the heavy rare earth element RH can be placed on the surface of the sintered compact together with the R1-M alloy and then the first heat treatment can be performed. Examples of the fluorides, oxides and oxyfluorides of the heavy rare earth element RH include TbF3, DyF3, Tb2O3, Dy2O3, TbOF and DyOF.

[0058] The R1-M alloy may be disposed in any position as long as at least a portion of the R1-M alloy is in contact with at least a portion of the sintered compact.

[0059] (Step of performing second heat treatment) The sintered body that has undergone the first heat treatment is then heat treated in a vacuum or inert gas atmosphere at a temperature of 400°C to 750°C, both inclusive, and lower than the temperature of the first heat treatment. In the present disclosure, this heat treatment is referred to as the second heat treatment. By performing the second heat treatment, high H cJ When the temperature at which the second heat treatment is performed (second heat treatment temperature) is higher than the first heat treatment temperature, or when the second heat treatment temperature is lower than 400°C or higher than 750°C, a high H cJ There is a possibility that you may not be able to obtain [Example]

[0060] The raw materials of each element were weighed so that the RTB-based sintered compacts had the compositions shown in Table 1, Nos. A to H, and alloys were produced by strip casting. The resulting alloys were coarsely pulverized by hydrogen pulverization to obtain coarsely pulverized powders. Next, zinc stearate was added as a lubricant to the resulting coarsely pulverized powders, and the mixture was then dry-pulverized in a nitrogen stream using an airflow pulverizer (jet mill) to obtain finely pulverized powders (alloy powders) with an average particle size d50 of 3 μm.

[0061] Zinc stearate was added as a lubricant to the finely pulverized powder, and after mixing, the powder was compacted in a magnetic field to obtain a powder compact. The compacting device used was a so-called perpendicular magnetic field compacting device (horizontal magnetic field compacting device), in which the magnetic field application direction and the pressure direction are perpendicular to each other. The obtained powder compact was sintered in a vacuum at 1000°C to 1090°C (a temperature selected for each sample at which sufficient densification by sintering occurs) for 4 hours to obtain an RTB-based sintered body. The density of the obtained RTB-based sintered body was 7.5 Mg / m 3 The results were as above. The composition of the obtained RTB-based sintered body is shown in Table 1. Each component in Table 1 was measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). The O (oxygen) content was measured using a gas analyzer based on gas fusion-infrared absorption, and the C (carbon) content was measured using a gas analyzer based on combustion-infrared absorption. The composition of the R1-M alloy (Table 2) was also measured using the same measurement method.

[0062] [Table 1]

[0063] The raw materials for each element were weighed so that the R1-M alloy had the approximate composition shown in No. a in Table 2. The raw materials were melted and then subjected to single-roll rapid cooling (melt spinning) to obtain ribbon or flake-shaped alloys. The resulting alloys were crushed in an argon gas atmosphere using a mortar and then passed through a 425 μm mesh sieve to prepare the R1-M alloy. The composition of the resulting R1-M alloy is shown in Table 2.

[0064] [Table 2]

[0065] The RTB sintered compacts No. A to H in Table 1 were cut and ground to form cubes measuring 7.4 mm x 7.4 mm x 7.4 mm. Next, 3 mass% of the R1-M alloy (No. a) was scattered over the entire surface of the RTB sintered compacts No. A to H, relative to 100 mass% of the RTB sintered compact. The RTB sintered magnet No. 1 shown in Table 3 was produced by carrying out a diffusion process using the RTB sintered compact No. A in Table 1 and the R1-M alloy No. a in Table 2. Nos. 2 to 8 are similarly described. The magnets were then subjected to a heat treatment (first heat treatment) at 900°C for 4 hours in a reduced pressure argon gas controlled at 50 Pa, followed by cooling to room temperature. Further, the magnets were subjected to a heat treatment (second heat treatment) at 480°C for 3 hours in a reduced pressure argon gas controlled at 50 Pa, followed by cooling to room temperature, to produce RTB sintered magnets (Nos. 1 to 8).

[0066] Table 3 shows the composition of the resulting RTB-based sintered magnet and the value of the middle part of equation (1) (i.e., [Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12([O] + [C]). Each component in Table 3 was measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). The O (oxygen) content was measured using a gas analyzer based on gas fusion-infrared absorption method, and the C (carbon) content was measured using a gas analyzer based on combustion-infrared absorption method.

[0067] The compositions in Table 3 are as follows: · Because the contents of Ce, La, Dy, and Tb were below the detection limit, the R content was calculated by adding up the Nd content and the Pr content. Since the Zn and Si contents were below the detection limit, the M content was calculated by adding up the Cu, Ga, and Al contents. Even if we assume that the sintered body contains up to 1 mass% of other elements, including Zr, the balance of T (Fe, Co) exceeds 61.5 mass%.

[0068] The obtained RTB sintered magnet was machined to make a magnet sample of 7 mm x 7 mm x 7 mm, and the magnetic properties (B r and H cJ ) were measured. The measurement results are shown in Table 3. In addition, EDX line analysis was performed on the cross sections of magnets No. 1 to 8, from the magnet surface to near the center of the magnet. It was confirmed that for all of Nos. 1 to 8, the Pr concentration and Cu concentration gradually decreased (gradually decreased) from the surface toward the depth (from the magnet surface toward the magnet center) within a range from the magnet surface to a depth of 200 μm. It was also confirmed that for all of Nos. 1 to 8, the Ga concentration did not gradually decrease from the surface toward the depth within a range from the magnet surface to a depth of 200 μm.

[0069] [Table 3]

[0070] As shown in Table 3, Nos. 2, 3, 5, and 6, which are examples of the present invention, do not contain Tb and have a residual magnetic flux density (B r ) is 1.40T or more, and coercive force (H cJ ) was 1300kA / m or more. Thus, it was possible to reduce the amount of heavy rare earth elements RH such as Tb while achieving a high B r and high H cJIn contrast, the comparative examples (Nos. 1, 4, 7, and 8) in which the M concentration and B concentration were outside the ranges of the present disclosure had a residual magnetic flux density (B r ) is 1.40T or higher, a high B r was obtained, but the coercive force (H cJ ) is less than 1300kA / m, and high H cJ was not obtained.

[0071] This application claims priority from Japanese Patent Application No. 2023-074816, filed April 28, 2023, the entire contents of which are incorporated herein by reference.

[0072] The disclosure of this specification may include the following aspects. (Aspect 1) R: 26.5 mass% or more and 31.5 mass% or less (R is a rare earth element, including one or two elements selected from the group consisting of Nd and Pr), M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu), B: 0.85% by mass or more and 0.94% by mass or less, and T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe by mass ratio), O: 0.05% by mass or more and 0.30% by mass or less, Tb: 0.20% by mass or less, and Dy: 0.30% by mass or less, and satisfies the following formula (1): the concentration of one or two elements selected from the group consisting of Nd and Pr and the concentration of Cu gradually decrease in a depth direction from the surface to a depth of 200 μm; An RTB sintered magnet that necessarily contains Ga as M, with the Ga content being at least 0.3 mass %, and in which the Ga concentration does not gradually decrease from the surface to a depth of 200 μm. 26.0 mass%≦([Nd]+[Pr]+[Ce]+[La]+[Dy]+[Tb])-12([O]+[C])≦27.7 mass% (1) Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O] and [C] are the contents of Nd, Pr, Ce, La, Dy, Tb, O and C, respectively, expressed in mass%. (Aspect 2) B: 0.85% by mass or more and 0.88% by mass or less. (Aspect 3) A method for producing the RTB based sintered magnet according to aspect 1, comprising: preparing an RTB-based sintered body; providing an R1-M alloy; a diffusion step of diffusing the R1-M alloy into the RTB based sintered compact, The RTB sintered body contains 0.3 mass % or more of Ga, The R1-M alloy is R1 is contained in an amount of 65% by mass or more and 95% by mass or less, wherein R1 is one or two selected from the group consisting of Nd and Pr, The alloy contains 5% by mass or more and 35% by mass or less of M, wherein M is at least one selected from the group consisting of Cu, Zn, and Si, and necessarily contains Cu; Manufacturing method for RTB sintered magnets. (Aspect 4) Aspect 4. A method for producing an RTB based sintered magnet according to aspect 3, wherein the RTB based sintered body further contains B: 0.85% by mass or more and 0.88% by mass or less. (Aspect 5) The RTB-based sintered body is moreover, R: 26.3 mass% or more and 31.3 mass% or less (R is a rare earth element and includes one or two elements selected from the group consisting of Nd and Pr), B: 0.85% by mass or more and 0.88% by mass or less, T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe by mass ratio), M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu); Tb: 0.20% by mass or less, and Dy: 0.30% by mass or less, and satisfy the following formula (2): A method for producing an RTB based sintered magnet according to aspect 3 or 4. 25.8 mass%≦([Nd]+[Pr]+[Ce]+[La]+[Dy]+[Tb])-12([O]+[C])≦27.5 mass% (2) Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O] and [C] are the contents of Nd, Pr, Ce, La, Dy, Tb, O and C, respectively, expressed in mass%.

Claims

1. A method for producing an RTB based sintered magnet, comprising the steps of: The RTB based sintered magnet is R: 26.5% by mass or more and 31.5% by mass or less (R is a rare earth element, including one or two selected from the group consisting of Nd and Pr), M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu), B: 0.85% by mass or more and 0.94% by mass or less, and T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T is Fe in terms of mass ratio), O: 0.05% by mass or more and 0.30% by mass or less, Tb: 0.20% by mass or less, and Dy: 0.30% by mass or less, and satisfies the following formula (1): The manufacturing method includes: a step of preparing an RTB-based sintered body; providing an R1-M alloy; a diffusion step of diffusing the R1-M alloy into the RTB-based sintered body, the R-T-B based sintered body contains 0.3 mass % or more of Ga, The R1-M alloy is R1 is contained in an amount of 65% by mass or more and 95% by mass or less, wherein R1 is one or two elements selected from the group consisting of Nd and Pr, The alloy contains 5% by mass or more and 35% by mass or less of M, wherein M is at least one selected from the group consisting of Cu, Zn, and Si, and necessarily contains Cu; A method for producing an RTB based sintered magnet. 26.0 mass%≦([Nd]+[Pr]+[Ce]+[La]+[Dy]+[Tb])-12([O]+[C])≦27.7 mass% (1) Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O] and [C] are the contents of Nd, Pr, Ce, La, Dy, Tb, O and C, respectively, expressed in mass %.

2. 2. The method for producing a sintered RTB based magnet according to claim 1, wherein the RTB based sintered body further contains B: 0.85% by mass or more and 0.88% by mass or less.

3. The RTB-based sintered body is moreover, R: 26.3 mass% or more and 31.3 mass% or less (R is a rare earth element and includes one or two elements selected from the group consisting of Nd and Pr), B: 0.85% by mass or more and 0.88% by mass or less, T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe in mass ratio), M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu), Tb: 0.20% by mass or less, and Dy: 0.30% by mass or less, and satisfy the following formula (2): The method for producing the RTB based sintered magnet according to claim 1 or 2. 25.8% by mass ≦ ​​([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12 ([O] + [C]) ≦ 27.5% by mass (2) Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O] and [C] are the contents of Nd, Pr, Ce, La, Dy, Tb, O and C, respectively, expressed in mass %.

4. 3. The method for producing a sintered RTB based magnet according to claim 1, wherein the Ga content contained in the RTB based sintered body is equal to or greater than the Ga content contained in the sintered RTB based magnet.

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