R-t-b sintered magnet

Abstract

Provided is an R-T-B sintered magnet containing 26.5-31.5 mass% of R (R is a rare earth element and contains, at least, one or two elements selected from the group consisting of Nd and Pr), 0.40-1.50 mass% of M (M is at least one element selected from the group consisting of Ga, Cu, Zn, Al and Si, and necessarily contains Cu), 0.85-0.94 mass% of B, and not less than 61.5 mass% of T (T is made of Fe and Co, and not less than 90% of T, in terms of mass ratio, is Fe), having 0.05-0.30 mass% of O, not more than 0.20 mass% of Tb, and not more than 0.30 mass% of Dy, and satisfying the expression below, wherein in a range from a surface to a depth of 200 μm, the concentration of the one or two elements selected from the group consisting of Nd and Pr and the Cu concentration gradually decreases in the depth direction from the surface. 26.0 mass% ≤ ([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12([O] + [C]) ≤ 27.7 mass%

Description

RTB system sintered magnet

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

[0002] R-T-B based 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 high-performance permanent magnets. For this reason, R-T-B based sintered magnets are used in a variety of motors in fields such as electric vehicles (EVs, HVs, and PHVs), renewable energy fields such as wind power generation, home appliances, and industrial applications. R-T-B based sintered magnets are essential materials for making these motors smaller, lighter, more efficient, and more energy-efficient (improving energy efficiency). Furthermore, R-T-B based sintered magnets are used in the drive motors of electric vehicles. The replacement of internal combustion engines with electric vehicles contributes to the prevention of global warming by reducing greenhouse gases such as carbon dioxide (fuel and exhaust gas emissions). In this way, R-T-B based sintered magnets are making a significant contribution to the realization of a clean energy society.

[0003] RTB based sintered magnets are mainly composed of R ２ T 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 (see, for example, Patent Document 1). ２ T １４ B main phase grain and two adjacent R ２ T １４ The present invention discloses a rare earth sintered magnet characterized in that it comprises a two-particle grain boundary phase between the R and B main phase crystal grains, the thickness of the two-particle grain boundary phase being 5 nm to 500 nm, and the phase having a magnetic property different from that of the ferromagnetic material. ２ T 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 based sintered magnets have a coercive force H ｃＪ (Hereafter, simply "H ｃＪTherefore, the R-T-B based sintered magnets used in electric vehicle motors in particular require high H ｃＪ i.e., higher H ｃＪ It is required to have the following.

[0005] JP 2014-209546 A

[0006] R ２ T １４ When the light rare earth elements RL (mainly Nd and Pr) in the B-type compounds are replaced with heavy rare earth elements RH (mainly Tb and Dy), H ｃＪ However, H ｃＪ While R ２ T １４ The saturation magnetization of the B-type compound phase decreases, resulting in a residual 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 avoid using Tb as much as possible (to minimize the amount used) and to use B ｒ While suppressing the decrease in 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 In recent years, especially in the motors for electric vehicles, ｒ and H ｃＪ 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.

[0009] Aspect 1 of the present invention is a composition comprising: 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); M: 0.40% by mass or more and 1.50% by mass or less (M is at least one element selected from the group consisting of Ga, Cu, Zn, Al and Si and must include 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 by mass); 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 the composition satisfies the following formula (1); The R-T-B based sintered magnet has a concentration of one or two elements selected from the group consisting of Nd and Pr, and a concentration of Cu that gradually decrease from the surface to a depth of 200 μm: 26.0% by mass≦([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) − 12([O] + [C])≦27.7% by mass (1), where [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] A second aspect of the present invention is the R-T-B based sintered magnet according to the first aspect, wherein M necessarily contains Ga, the Ga content is 0.3 mass % or more, and the Ga concentration does not gradually decrease within a range from the surface to a depth of 200 μm.

[0011] According to an embodiment of the present invention, the amount of heavy rare earth elements RH such as Tb is reduced while B ｒ and H ｃＪ Therefore, it is possible to provide an RTB based sintered magnet with further improved properties.

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

[0013] The present inventors have been developing a method for improving the magnetic properties (particularly, B) of an RTB-based sintered magnet while reducing the amount of heavy rare earth used. ｒ and H ｃＪ) and found that the B content of the R-T-B based sintered magnet is ２ T １４ It has been found that in the case of a "low boron" composition, which is lower than the stoichiometric composition of the B compound, 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. ２ T １４ It was found that the same effect can be obtained even if a part of B in the B compound is replaced by carbon (C). ２ T １４ It was found that the C that had substituted for B in the B compound bonded with the rare earth oxide in the grain boundary during the sintering process, generating a rare earth oxygen carbon compound (R-O-C compound) in the grain boundary. It was also found that the atomic ratio in this case was R:(C,O)=1:1. When such an R-O-C compound was generated in the grain boundary, it contributed to the formation of the R, which is the main phase. ２ T １４ The content of C constituting the B compound decreases. ２ T １４ Even if a part of B in the B compound is replaced by C, the effect of "low boron" can be obtained. ２ T １４ A decrease in the content of C that constitutes the B compound effectively reduces the total amount of B and C. Furthermore, the formation of R-O-C compounds at grain boundaries means that a portion of the rare earth element R contained in the raw alloy is consumed in the production of the R-O-C compound. Note that R-O-C compounds (rare earth oxycarbides) include R-O compounds (rare earth oxides) and R-C compounds (rare earth carbides).

[0014] Based on the above, the inventors hypothesized that when diffusing rare earth element R or metal element M from the surface to the interior of a low-boron R-T-B based sintered magnet, the thickness and structure of the grain boundaries must be controlled to optimize the magnetic property improvement effect of diffusion, and that to do so, the contents of R, O, and C must satisfy an appropriate relationship. Furthermore, the inventors hypothesized that controlling the R content to an appropriate level enhances the magnetic property improvement effect of R and M due to grain boundary diffusion in a low-boron R-T-B based sintered magnet. Based on these findings, the inventors conducted further studies and discovered that an R-T-B based sintered magnet with excellent magnetic properties can be obtained by diffusing R (Nd and Pr) and Cu from the magnet surface into an R-T-B based sintered magnet with a specific component composition that satisfies the following formula (1) and in which the contents of B and M (Ga, Cu, Zn, Al, and Si) are appropriately controlled. This led to the completion of the invention according to the present embodiment.

[0015] The R sintered magnet according to the embodiment (hereinafter sometimes simply referred to as "sintered magnet") will be described in detail below.

[0016] <RTB based sintered magnet> The R-T-B based sintered magnet contains: 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); M: 0.40% by mass or more and 1.50% by mass or less (M is at least one element selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must include 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 by mass); 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.

[0017] The heavy rare earth elements RH (especially Tb and Dy) contained in the sintered magnet are preferably contained in a smaller amount than conventionally. The sintered magnet does not necessarily contain RH. In other words, the lower limit of the RH content in the sintered magnet is 0% by mass. The Tb content is preferably limited to 0.10% by mass or less. Furthermore, the Dy content is preferably limited to 0.20% by mass or less.

[0018] The sintered magnet satisfies the following formula (1): 26.0% by mass≦([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) − 12([O] + [C])≦27.7% by mass (1), where [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%. Note that if the sintered magnet does not contain one or more of Nd, Pr, Ce, La, Dy, Tb, O, and C, the content of the absent element is considered to be “0% by 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 ｃＪ The C (carbon) content in the sintered magnet is preferably 0.05% by mass or more and 0.18% by mass or less. The C content can be adjusted by the amount of lubricant added during pulverization or molding. Preferably, formula (1) is 26.0% by mass or more and 27.5% by mass or less, more preferably 26.3% by mass or more and 27.4% by mass or less, and particularly preferably 27.0% by mass or more and 27.4% by mass or less. A high B content can be obtained while further reducing the amount of heavy rare earth element RH such as Tb used. 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 content of R is 26.5% by mass or more and 31.5% by mass or less. If the content of R is less than 26.5% by mass, it may be difficult to densify the sintered material. If the content of R exceeds 31.5% by mass, the ratio of the main phase decreases, and the B content may be reduced. 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 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 The sintered magnet necessarily contains Cu as M, but preferably also contains Ga. ｃＪ can be further improved.

[0023] Furthermore, as a result of further investigations, the present 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 part 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 alloy for a sintered magnet), 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 It has been newly discovered that the above can be achieved. That is, the sintered magnet of the present disclosure must contain Cu and Ga as M, the Ga content is 0.3 mass% or more, and preferably 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 not more than 0.70% by mass, Zn: 0% by mass or more and not more than 0.2% by mass, Al: 0% by mass or more and not more than 0.8% by mass, and Si: 0% by mass or more and not more than 0.2% by mass.

[0026] (B: 0.85% by mass or more and 0.94% by mass or less) The B content is 0.85% by mass or more and 0.94% by mass or less. By containing B within the range of the present disclosure, the sintered magnet can have a high H ｃＪ The 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% by mass or more and 0.30% by 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 ｃｊ However, if it is contained in excess, B ｒ Since Tb is a scarce resource and its production area is limited, it is desirable to reduce the amount used as much as possible, and it is preferable that Tb is not contained (i.e., the Tb content is 0 mass %).

[0029] (Dy: 0.30% by 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 content of T contained in the sintered magnet is 61.5% by mass or more, and B ｒ It is particularly preferable that the balance in the component composition of the sintered magnet is T and inevitable impurities. For example, if the sintered magnet contains R, M, B, O, and C, but does not contain Tb, Dy, or any optional additional elements described below, it is preferable that the balance of R, M, B, O, and C is T and inevitable impurities. Co may be contained as part of T, which can improve corrosion resistance, but if the ratio of the Co content to the T content exceeds 10%, high B ｒ may not be obtained.

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

[0032] In the sintered magnet according to the 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 Cu concentration 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 diffusion process from the magnet surface to the interior of the magnet using a diffusion source containing one or two elements selected from the group consisting of Nd and Pr and Cu during the production of the sintered magnet. By carrying out a diffusion process during the production of the sintered magnet, the magnetic properties of the resulting sintered magnet can be improved. It is preferable that the Ga concentration does not gradually decrease from the surface to a depth of 200 μm. In other words, it is preferable not to carry out a diffusion process using a diffusion source containing Ga.

[0033] The concentrations of Nd, Pr, and Cu in the range from the surface to a depth of 200 μm can be confirmed by linear analysis (line analysis) using energy dispersive X-ray spectroscopy (EDX) in the cross section of the sintered magnet, from the magnet surface toward the center of the magnet to a depth of 200 μm. It is preferable to measure in a direction perpendicular to the surface and at least 200 μm away from the edge of the surface. When performing line analysis, measurements are performed in a direction perpendicular to the surface (the periphery of the measured cross section) in a region at least 200 μm away from the edge of the measured cross section, so as not to measure within 200 μm of the periphery of the measured cross section. The Ga concentration can also be confirmed by similar measurements.

[0034] <Method for Manufacturing Sintered RTB Based Magnet> Hereinafter, an embodiment of a method for manufacturing a sintered RTB based magnet according to the present disclosure will be described.

[0035] As shown in FIG. 1 , the manufacturing method of this embodiment can include step S10 of preparing an R-T-B based sintered body, step S20 of preparing an R1-M alloy, step S30 of performing a first heat treatment, and step S40 of performing a second heat treatment. Step S30 is a diffusion step in which at least a portion of the R1-M alloy is brought into contact with at least a portion of the surface of the R-T-B based sintered body, and the first heat treatment is performed in a vacuum or inert gas atmosphere at a temperature of 700°C or higher and 950°C or lower, thereby diffusing R1 and M into the magnet. Step S40 is a second heat treatment in a vacuum or inert gas atmosphere on the R-T-B based sintered magnet that has undergone the first heat treatment, at a temperature of 400°C or higher and 750°C or lower, which is lower than the first heat treatment temperature. Each of these steps will be described in more detail below.

[0036] (Step of Preparing an RTB-Based Sintered Body) First, the composition of the RTB-based 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, and carbon 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 the diffusion process described below, excessive diffusion of R and M into the sintered body is prevented, and grain boundary diffusion can be significantly promoted.

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

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

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

[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 they are 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 makes it easier for the alloy to 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. 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] The fine powder used to prepare the sintered body 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) as long as it satisfies the above-mentioned conditions.

[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 due to 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 heat treatment 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] (Step of Preparing R1-M Alloy) In this embodiment, R1 and M are diffused from the surface to the interior of the sintered body. For this purpose, an alloy containing the elements to be diffused (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 content of R1 is preferably 65% ​​by mass to 95% by mass, and more preferably 70% by mass 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 content of M is preferably 5% by mass to 35% by mass, and more preferably 5% by mass 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 may be any shape, such as a film, foil, powder, block, or particle.

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

[0054] The R1-M alloy can be prepared using a raw material alloy production method commonly employed 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 Performing First Heat Treatment (Diffusion Step)) At least a portion of the surface of the sintered body prepared by the method described above is brought into contact with at least a portion of the R1-M alloy, and the first heat treatment is performed 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 step for diffusing R1 and M into the interior of the sintered body (i.e., the diffusion step), 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 a 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 in which the R1-M alloy is dispersed in a dispersing medium can be applied to the surface of the sintered compact, and the dispersing medium can then 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, for example, a known sputtering device can be used to form an R1-M alloy film on the surface of the sintered compact, followed by the first heat treatment. Furthermore, when introducing a heavy rare earth element (RH) into the sintered compact, in addition to using an R1-M alloy containing RH, a fluoride, oxide, oxyfluoride, or the like of the heavy rare earth element (RH) can also be placed on the surface of the sintered compact and the first heat treatment can be performed. Examples of fluorides, oxides, and oxyfluorides of the heavy rare earth element (RH) include TbF. ３ , DyF ３ , Tb ２ O ３ , Dy ２ O ３ , 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 body.

[0059] (Step of performing second heat treatment) The sintered body that has undergone the first heat treatment is subjected to heat treatment in a vacuum or inert gas atmosphere at a temperature of 400°C or higher and 750°C or lower, which is lower than the first heat treatment temperature. 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

[0060] The raw materials of each element were weighed so that the R-T-B system sintered bodies had the compositions shown in Table 1, Nos. A to H, and alloys were produced by strip casting. Each of the obtained alloys was coarsely pulverized by hydrogen pulverization to obtain coarsely pulverized powder. Next, zinc stearate was added as a lubricant to the obtained coarsely pulverized powder and mixed, and then dry-pulverized in a nitrogen gas stream using an airflow pulverizer (jet mill device) to obtain finely pulverized powder (alloy powder) 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 at which sufficient densification by sintering occurs for each sample) for 4 hours to obtain an R-T-B based sintered body. The density of the obtained R-T-B based sintered body was 7.5 Mg / m ３ The results were as above. The compositions of the obtained R-T-B based sintered bodies are shown in Table 1. Each component in Table 1 was measured using high-frequency inductively coupled plasma optical emission spectroscopy (ICP-OES). The O (oxygen) content was measured using a gas analyzer that employs the gas fusion-infrared absorption method, and the C (carbon) content was measured using a gas analyzer that employs the combustion-infrared absorption method. The composition of the R1-M alloy (Table 2) was also measured using the same measurement method.

[0062]

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

[0064]

[0065] The R-T-B based 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 R-T-B based alloy (No. a) was scattered over the entire surface of each of the R-T-B based sintered compacts No. A to H, relative to 100 mass % of the R-T-B based sintered compact. The R-T-B based sintered magnet No. 1 shown in Table 3 was obtained by performing a diffusion process using the R-T-B based sintered compact No. A in Table 1 and the R1-M alloy No. a in Table 2. Nos. 2 to 8 are described similarly. Subsequently, the magnets were subjected to a heat treatment (first heat treatment) at 900°C for four hours in reduced-pressure argon gas controlled to 50 Pa, and then cooled to room temperature. Further, a heat treatment (second heat treatment) was carried out at 480°C for 3 hours in reduced pressure argon gas controlled at 50 Pa, and then the magnet was cooled to room temperature to produce RTB based sintered magnets (Nos. 1 to 8).

[0066] Table 3 shows the composition of the resulting R-T-B 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: Since 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 contents of Zn and Si were below the detection limit, the M content was calculated by adding up the Cu content, Ga content, and Al content. Even assuming that other elements, including Zr detected in the sintered body, are contained at a maximum of about 1 mass%, the remainder T (Fe, Co) exceeded 61.5 mass%.

[0068] The obtained RTB based sintered magnet was machined to obtain 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, linear analysis (line analysis) was performed using EDX 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 No. 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 No. 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]

[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 the coercive force (H ｃＪ ) was 1300 kA / m or more. Thus, it is possible to reduce the amount of heavy rare earth elements RH such as Tb while achieving high B ｒ and high H ｃＪ In 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 more, a high B ｒ was obtained, but the coercive force (H ｃＪ ) is less than 1300 kA / m, and high H ｃＪ was not obtained.

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

Claims

1. 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 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): In a range from the surface to a depth of 200 μm, 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, An R-T-B based sintered magnet which necessarily contains Ga as M, has a Ga content of 0.3 mass % or more, and has a Ga concentration that does not decrease gradually within a range 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 %.

2. An R-T-B based sintered magnet as described in claim 1, wherein B is 0.85 mass % or more and 0.88 mass % or less.

3. A method for producing the R-T-B based sintered magnet according to claim 1, comprising the steps of: A step of preparing an R-T-B based sintered body; providing an R1-M alloy; a diffusion step of diffusing the R1-M alloy into the R-T-B system sintered compact, 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 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, where 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.

4. A method for producing an R-T-B based sintered magnet as described in claim 3, wherein the R-T-B based sintered body further contains B: 0.85 mass% or more and 0.88 mass% or less.

5. The R-T-B based sintered body, moreover, R: 26.3 mass% or more and 31.3 mass% or less (R is a rare earth element and includes one or two 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 terms of 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 satisfying the following formula (2): The method for producing an RTB based sintered magnet according to claim 3 or 4. 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 %.