Manufacturing method of r-t-b based sintered magnet

Abstract

To provide a manufacturing method of an R-T-B based sintered magnet capable of reducing an amount of heavy rare earth element RH to be used and improving the HcJ of an R-T-B based sintered magnet as compared with a conventional diffusion method.SOLUTION: A manufacturing method of an R-T-B based sintered magnet includes: a sintered magnet material preparation step of preparing an R-T-B based sintered magnet material (R is a rare earth element, T is Fe or Fe and Co, and B is boron); a diffusion source preparation step of preparing a diffusion source powder formed from an alloy containing a rare earth element; an attachment step of attaching the diffusion source powder to a surface of the R-T-B based sintered magnet material; and a heat treatment step of heat-treating the R-T-B based sintered magnet material to which the diffusion source powder is attached at a temperature equal to or lower than a sintering temperature of the R-T-B based sintered magnet material. The heat treatment step is performed in an inert gas atmosphere of 10 kPa or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing an RTB based sintered magnet. [Background technology]

[0002] R2T 14 RTB-based sintered magnets, which have a B-type compound as their main phase, are known as the most high-performance permanent magnets, and are used in a variety of motors in the automotive sector, including electric vehicles (EVs, HVs, PHVs), renewable energy sectors such as wind power generation, home appliances, and industrial sectors.

[0003] RTB sintered magnets are mainly R2T 14 It consists of a main phase made of B compounds and a grain boundary phase located at the grain boundaries of this main phase. 14 B compounds are ferromagnetic materials with high saturation magnetization and anisotropic magnetic field, and form the basis of the properties of RTB-based sintered magnets.

[0004] RTB sintered magnets have a coercive force H cJ (Hereafter, simply "H cJ This causes irreversible thermal demagnetization. Therefore, RTB sintered magnets, which are used in electric vehicle motors in particular, have a high H cJ Sintered magnets that satisfy this requirement have a high H cJ is required.

[0005] In RTB sintered magnets, R2T 14 When a part of the light rare earth element RL (e.g., Nd and / or Pr) contained in R in the B compound is replaced with a heavy rare earth element RH (e.g., Dy and / or Tb), H cJ It is known that the H cJHowever, RH, especially Tb and Dy, have limited resources and are produced in limited areas, which means that their supply is unstable and their prices fluctuate greatly. Therefore, it is necessary to reduce the amount of RH used or to use no RH at all and produce H. cJ It is required to improve.

[0006] Patent Document 1 describes a method for diffusing Pr after performing a step of diffusing at least one of Dy and Tb, thereby concentrating at least one of Dy and Tb in the outer periphery of the main phase crystal grains, and achieving a higher H cJ The present invention describes an RTB-based sintered magnet that exhibits the above properties and a method for producing the same.

[0007] Patent Document 2 describes a process in which an RTB sintered magnet body and an RH diffusion source containing a heavy rare earth element RH (at least one of Dy and Tb) and 30 mass % to 80 mass % Fe are placed in a treatment chamber so that they can be moved relatively and in close proximity or in contact with each other, and heated while being moved continuously or intermittently, thereby efficiently diffusing the heavy rare earth element RH into the RTB sintered magnet body in a short time, and increasing the residual magnetic flux density B r (Hereafter, simply "B r ") without lowering H cJ A method for producing an RTB-based sintered magnet that improves the magnet's properties is described.

[0008] Patent Document 3 describes a process of preparing a diffusion source powder formed from a powder of an RTB sintered magnet and an alloy or compound of a heavy rare earth element RH, which is at least one of Dy and Tb; applying an adhesive to a coating area on the surface of the RTB sintered magnet, adhering the diffusion source powder by a fluidized bed method, and heat-treating the magnet to diffuse the heavy rare earth element RH from the surface to the inside, thereby reducing the amount of heavy rare earth element RH used and increasing the H of the RTB sintered magnet. cJ A method for producing an RTB-based sintered magnet that improves the magnet's properties is described. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-130888 [Patent Document 2] International Publication No. 2013 / 108830 [Patent Document 3] Japanese Patent Application Publication No. 2019-135771 Summary of the Invention [Problem to be solved by the invention]

[0010] Patent Document 1 uses a diffusion method in which an RTB sintered compact and Dy metal serving as a diffusion source are separated by a Nb mesh, followed by heat treatment. After that, Pr metal powder is scattered on the surface of the sintered compact and heat treatment is performed, thereby concentrating the heavy rare earth element RH in the outer periphery of the main phase crystal grains. Patent Document 2 also uses a method in which a diffusion source containing the heavy rare earth element RH is moved continuously or intermittently while heat treatment is performed, thereby diffusing the heavy rare earth element RH into the magnet. These methods have the problem of requiring a large amount of diffusion source. In contrast, Patent Document 3 uses a method in which the diffusion source is applied uniformly and efficiently to the magnet surface, without waste, and then heat treatment is performed, thereby reducing the amount of diffusion source required. In both cases, a diffusion method that further reduces the amount of heavy rare earth element RH used has been desired.

[0011] The embodiment of the present disclosure can reduce the amount of heavy rare earth element RH used compared to conventional diffusion methods, and can also reduce the amount of H in RTB-based sintered magnets. cJ It is possible to provide a method for producing an RTB-based sintered magnet that can improve the properties of the magnet. [Means for solving the problem]

[0012] A method for producing an RTB based sintered magnet according to one embodiment of the present disclosure includes a sintered magnet material preparation step of preparing an RTB based sintered magnet material (R is a rare earth element, T is Fe or Fe and Co, and B is boron), a diffusion source preparation step of preparing a diffusion source powder formed from an alloy containing a rare earth element, an attachment step of adhering the diffusion source powder to the surface of the RTB based sintered magnet material, and a heat treatment step of heat treating the RTB based sintered magnet material with the diffusion source powder attached at a temperature equal to or lower than the sintering temperature of the RTB based sintered magnet material, wherein the heat treatment step is carried out in an inert gas atmosphere of 10 kPa or higher.

[0013] In the method for producing an RTB based sintered magnet according to one aspect of the present disclosure, the diffusion source powder contains at least Pr and / or Nd as a rare earth element.

[0014] In one aspect of the method for producing an RTB based sintered magnet according to the present disclosure, the diffusion source powder contains a metal element other than a rare earth element.

[0015] In the method for producing an RTB based sintered magnet according to one aspect of the present disclosure, the metal element other than the rare earth element is at least one selected from the group consisting of Al, Cu, Zn, Ga, Fe, Co, and Ni.

[0016] In the method for producing an RTB based sintered magnet according to one aspect of the present disclosure, in the adhering step, an adhesive is applied to the surface of the RTB based sintered magnet material, and the diffusion source powder is adhered thereto.

[0017] In the method for producing an RTB based sintered magnet according to one aspect of the present disclosure, in the heat treatment step, an inert gas atmosphere of 10 kPa or more is maintained from before the heat treatment until the end of the heat treatment.

[0018] In one aspect of the method for producing an RTB based sintered magnet of the present disclosure, the heat treatment temperature in the heat treatment step is equal to or higher than the melting point of the diffusion source powder.

[0019] In one aspect of the method for producing an RTB based sintered magnet of the present disclosure, the heat treatment temperature in the heat treatment step is 500°C or higher and 1000°C or lower.

[0020] In one aspect of the present disclosure, in the method for producing an RTB based sintered magnet, the atomic ratio of B to T in the RTB based sintered magnet material is R2T 14 This is lower than the atomic ratio of B to T in the stoichiometric composition of the B compound.

[0021] In the method for producing an RTB based sintered magnet according to one aspect of the present disclosure, in the sintered magnet material preparation step, the B content in the RTB based sintered magnet material is 0.80 mass % or more and 0.99 mass % or less. [Effects of the Invention]

[0022] According to the embodiment of the present disclosure, it is possible to reduce the amount of heavy rare earth element RH used compared to conventional diffusion methods, and also to improve the H content of RTB based sintered magnets. cJ It is therefore possible to provide a method for producing an RTB based sintered magnet that can improve the properties. [Brief explanation of the drawings]

[0023] [Figure 1] 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 disclosure. [Figure 2] 1 is a graph showing the relationship between the coercive force HcJ and the furnace pressure for RTB based sintered magnets obtained using RTB based sintered magnet materials No. 1, No. 2, and No. 3 of Example 1. [Figure 3] 1 is a graph showing the relationship between the coercive force HcJ and the furnace pressure for RTB based sintered magnets obtained using RTB based sintered magnet materials No. 4 and No. 5 of Example 1. [Figure 4] 1 is a graph showing the relationship between the coercive force HcJ and the furnace pressure for RTB based sintered magnets obtained using RTB based sintered magnet materials No. 6 and No. 7 of Example 1. [Figure 5]1 is a graph showing the relationship between the coercive force HcJ and the furnace pressure for RTB based sintered magnets obtained using RTB based sintered magnet materials Nos. 8, 9, and 10 of Example 2. [Figure 6] 1 is a graph showing the relationship between the coercive force HcJ and the furnace pressure for RTB based sintered magnets obtained using RTB based sintered magnet materials No. 11 and No. 12 of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0024] An embodiment of a method for manufacturing an RTB based sintered magnet according to the present disclosure will now be described. A flowchart of the method for manufacturing an RTB based sintered magnet in this embodiment is shown in Figure 1. The method for manufacturing an RTB based sintered magnet in this embodiment includes a sintered magnet material preparation step S10 in which an RTB based sintered magnet material (R is a rare earth element, T is Fe or Fe and Co, and B is boron) is prepared, a diffusion source preparation step S20 in which a diffusion source powder formed from an alloy containing a rare earth element is prepared, an attachment step S30 in which the diffusion source powder is adhered to the surface of the RTB based sintered magnet material, and a heat treatment step S40 in which the RTB based sintered magnet material with the diffusion source powder adhered thereto is heat treated at a temperature below the sintering temperature of the RTB based sintered magnet material, and the heat treatment step is carried out in an inert gas atmosphere of 10 kPa or higher.

[0025] The present inventors have long known that when heat treatment is performed while moving the diffusion source continuously or intermittently, as in the method described in Patent Document 2, there is no dependency on the heat treatment atmosphere (pressure) when the diffusion source is supplied to the sintered magnet material. However, when they checked whether there was a similar dependency on the heat treatment atmosphere (pressure) when the diffusion source was applied uniformly and efficiently to the magnet surface without waste, as in the method described in Patent Document 3, they found that unexpected results were obtained, which led to the embodiment of the present disclosure.

[0026] 1. RTB-based sintered magnet material preparation process S10 First, the sintered magnet material preparation step S10 for preparing an RTB sintered magnet material (R is a rare earth element, and T is Fe or Fe and Co) will be described. Any known RTB sintered magnet material can be used, and for example, it has the following composition: Rare earth element R: 27.5mass% or more and 35.0mass% or less, B (a part of B (boron) may be substituted with C (carbon)): 0.80 mass% or more and 0.99 mass% or less, Ga: 0.8 mass% or less (including 0 mass%) Additional element X (at least one selected from the group consisting of Al, Cu, Zr, and Nb): 2 mass% or less (including 0 mass%), T (a transition metal element mainly consisting of Fe, which may contain Co) and unavoidable impurities: the balance However, it is preferable to satisfy the following inequality (1): [T] / 55.85>14[B] / 10.8 (1) ([T] is the T content expressed in mass%, and [B] is the B content expressed in mass%) Here, the rare earth element R may contain a heavy rare earth element RH, but preferably consists mainly of a light rare earth element RL (at least one element selected from Nd and Pr). When a heavy rare earth element RH is contained, it is preferable that at least one of Dy and Tb is contained. Inequality (1) expresses the B content relative to T in an RTB-based sintered magnet material as R2T 14 This indicates that the B content relative to T in the stoichiometric composition of the B compound should be lower than that of the B compound. By using such an RTB-based sintered magnet material, the amount of heavy rare earth element RH used can be reduced, or even if no heavy rare earth element RH is used, high H cJ can be obtained.

[0027] The RTB sintered magnet material having the above composition can be manufactured by any known manufacturing method. For example, a raw material alloy produced by strip casting or the like is crushed using a jet mill or the like to a particle size D50 of 2.0 μm to 4.5 μm, then molded in a magnetic field and sintered at a temperature of 900°C to 1100°C to produce a sintered body. Crushing to a particle size D50 of 2.0 μm to 4.5 μm results in a high B r and high H cJ Preferably, the particle size D50 is 2.5 μm or more and 3.5 μm or less. By adjusting the particle size D50 within a preferred range, it is possible to suppress deterioration in productivity and obtain a higher B content without using a precious heavy rare earth element RH. r and high H cJ can be obtained. Particle size D50 is the particle size at which the cumulative particle size distribution (volume basis) from the small diameter side reaches 50% in the particle size distribution obtained by laser diffraction analysis using the airflow dispersion method. Particle size D50 can be measured, for example, using a particle size distribution measuring device "HELOS&RODOS" manufactured by Sympatec under conditions of dispersion pressure: 4 bar, measurement range: R2, and measurement mode: HRLD. The process of preparing an RTB-based sintered magnet material is a process of obtaining an RTB-based sintered magnet material to be subjected to the heat treatment process described below, and includes a mode in which the RTB-based sintered magnet material is prepared by the user prior to the heat treatment process, as well as a mode in which an RTB-based sintered magnet material prepared separately is obtained. The RTB-based sintered magnet material may be in the as-sintered state, or may have been subjected to cutting or polishing processes.

[0028] 2. Diffusion source preparation step S20 Next, a diffusion source preparation step S20 for preparing a diffusion source powder formed from a powder of an alloy containing a rare earth element will be described. The diffusion source powder is preferably formed from a powder of an alloy of a rare earth element R and a metal element M (hereinafter, sometimes referred to as an "RM-based alloy").

[0029] The rare earth element R is preferably a light rare earth element RL. The light rare earth element RL preferably contains at least Pr and / or Nd, more preferably consists of Pr and / or Nd, and even more preferably consists of Pr. Here, "Pr and / or Nd" is synonymous with "Pr, or Nd, or Pr and Nd." Furthermore, the rare earth element R preferably accounts for 65 to 97 mass% of the entire alloy, more preferably 70 mass% to 95 mass%, and even more preferably 85 mass% to 93 mass%. When the rare earth element R consists of Pr, 20 mass% or less of Pr can be substituted with Nd, and 30 mass% or less of Pr can be substituted with Dy and / or Tb. La, Ce, etc. may be contained as needed.

[0030] The metal element M is preferably at least one selected from the group consisting of Al, Cu, Zn, Ga, Fe, Co, and Ni. The content of the metal element M is preferably 5 mass% or more and 30 mass% or less of the entire alloy, and more preferably 7 mass% or more and 15 mass% or less. By selecting a preferred embodiment, a higher H cJ Furthermore, M preferably contains at least Cu, and may further contain Ga. Typical examples of RM alloys are PrCu alloy, NdCu alloy, NdPrCu alloy, PrCuGa alloy, NdCuGa alloy, NdPrCuGa alloy, PrTbCu alloy, PrTbCuGa alloy, etc. In addition to the above elements, small amounts of unavoidable impurity elements such as Si, Mn, O, C, and N may be contained.

[0031] The method for producing the diffusion source powder is not particularly limited. It may be produced by a method in which an alloy ribbon is produced by roll quenching and then pulverized, or by a known atomization method such as centrifugal atomization, rotating electrode atomization, gas atomization, or plasma atomization. The particle size of the diffusion source powder is, for example, 500 μm or less, and as small as about 10 μm. The step of preparing the diffusion source is a step of obtaining alloy powder to be subjected to the heat treatment step described below, and includes a mode in which the diffusion source is produced by the diffusion source itself prior to the heat treatment step, as well as a mode in which a separately produced RM-based alloy is obtained.

[0032] 3. Adhesion step S30 Next, the adhering step S30 of adhering the diffusion source powder to the surface of the RTB based sintered magnet material will be described.

[0033] When adhering the diffusion source powder to the surface of the RTB sintered magnet material, it is preferable to first coat the surface of the RTB sintered magnet material with an adhesive or pressure-sensitive adhesive. Examples of pressure-sensitive adhesives include PVA (polyvinyl alcohol), PVB (polyvinyl butyral), and PVP (polyvinylpyrrolidone). Any method can be used to apply the pressure-sensitive adhesive to the surface of the RTB sintered magnet material. Specific examples of application methods include spraying, immersion (dipping), and application with a dispenser. The pressure-sensitive adhesive may be applied to the entire surface, or it may be applied to only a portion of the surface.

[0034] The diffusion source powder is preferably set so that the powder particles adhere to the surface of the RTB-based sintered magnet material and are within a desired adhesion amount relative to the RTB-based sintered magnet material. The adhesion amount is expressed as the percentage increase in mass %, with the mass ratio of the sintered magnet material before diffusion being 100%. For example, an adhesion amount of 1 mass % to 6 mass % is preferred, and 1.5 mass % to 3.5 mass % is even more preferred. The particle size can be determined by experiment and / or calculation to achieve the desired adhesion amount. Experiments to determine the particle size are preferably conducted in accordance with the actual manufacturing method. The particle size may be adjusted, for example, by sieving. Furthermore, a binder may be used for granulation to achieve the desired particle size range.

[0035] 4. Heat treatment process S40 Next, we will explain the heat treatment step S40, in which the RTB based sintered magnet material to which the diffusion source powder has been attached is heat treated at a temperature below the sintering temperature of the RTB based sintered magnet material. This heat treatment step diffuses the elements (rare earth element R, metal element M) contained in the diffusion source powder from the surface to the interior of the RTB based sintered magnet material. Therefore, hereinafter, the heat treatment step S40 may be referred to as the "diffusion step S40" and the heat treatment step may be referred to as the "diffusion step." By performing this heat treatment step (diffusion step) in an inert gas atmosphere of 10 kPa or more, the diffusion source powder attached to the RTB based sintered magnet material is efficiently diffused. In other words, a small amount of attached powder can achieve high H cJ Therefore, even if the amount of the heavy rare earth element RH is reduced or no heavy rare earth element RH is used, the H of the RTB sintered magnet can be obtained. cJ can be improved.

[0036] In a more preferred embodiment, an RTB based sintered magnet material containing the entire Ga content targeted for the RTB based sintered magnet is prepared, and a diffusion source not containing Ga, such as a PrCu alloy, is prepared in the diffusion source preparation step, and the heat treatment step is carried out in an inert gas atmosphere of 10 kPa or more, thereby achieving more efficient diffusion and increasing the H content of the RTB based sintered magnet. cJ can be further improved.

[0037] The inert gas is preferably a gas inert to the RTB-based sintered magnet material and the diffusion source powder, and a rare gas such as argon is preferably used. The pressure of the inert gas atmosphere is 10 kPa or higher, more preferably 100 kPa or higher, and particularly preferably 110 kPa or higher, which is higher than atmospheric pressure. Considering the strength of the furnace and container used in the heat treatment process, the upper limit of the pressure is preferably 1 GPa or lower. To control the atmosphere (pressure), the RTB-based sintered magnet material to which the diffusion source powder is attached is placed so that the pressure is equal to that inside the furnace (container), and the pressure inside the furnace can be controlled using an exhaust valve set to a predetermined pressure while preventing backflow and an inert gas introduction valve set to a constant flow rate and pressure.

[0038] The heat treatment temperature in the heat treatment step is equal to or lower than the sintering temperature of the RTB based sintered magnet (specifically, for example, 1000°C or lower). The temperature is preferably higher than the melting point of the diffusion source powder, for example, 500°C or higher. The heat treatment time is preferably, for example, 10 minutes to 72 hours. After the heat treatment, if necessary, a heat treatment at 400 to 700°C for 10 minutes to 72 hours may be performed (this heat treatment is for improving the magnetic properties, and may be referred to as a "second heat treatment" hereinafter to distinguish it from the heat treatment in the heat treatment step).

[0039] In the heat treatment step, it is preferable to maintain an inert gas atmosphere of 10 kPa or more from before the heat treatment (for example, from the room temperature stage) until the heat treatment is completed (until the holding at the heat treatment temperature is completed, i.e., until cooling is started).

[0040] According to the method for producing an RTB based sintered magnet described above, it is possible to reduce the amount of heavy rare earth element RH used compared to conventional diffusion methods, and also to reduce the H cJ It is therefore possible to provide a method for producing an RTB based sintered magnet that can improve the properties. [Example]

[0041] The embodiments of the present disclosure will be described in more detail with reference to examples, but the embodiments of the present disclosure are not limited thereto. [Example]

[0042] [Preparing RTB sintered magnet material] Each element was weighed to obtain the composition of the RTB-based sintered magnet material shown in Table 1 (excluding O, N, and C), and raw 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 coarsely pulverized powder in an amount of 0.035 mass% relative to 100 mass% of the coarsely pulverized powder, and the mixture was mixed. The coarsely pulverized powder containing the lubricant was then finely pulverized using a jet mill. A finely pulverized powder with a particle size D50 of 2.6 μm was obtained by fine pulverization. D50 was measured using a particle size distribution analyzer "HELOS&RODOS" manufactured by Sympatec under the following conditions: dispersion pressure: 4 bar, measurement range: R2, and measurement mode: HRLD.

[0043] The resulting finely pulverized powder was mixed with zinc stearate (0.05 mass% relative to 100 mass% of the finely pulverized powder) as a lubricant and compacted in a magnetic field to obtain a green body. 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 pressure direction are perpendicular to each other. The resulting green body was sintered in a vacuum for four hours (a temperature selected to ensure sufficient densification by sintering), and then rapidly cooled to obtain an RTB-based sintered magnet material. The resulting RTB-based sintered magnet material had a density of 7.5 Mg / m 3 That was all.

[0044] To determine the composition of the resulting RTB-based sintered magnet material, the contents of Nd, Pr, Fe, Co, Al, Ga, Cu, Zr, and B were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). The oxygen content (O) of the RTB-based sintered magnet material was measured using a gas fusion-infrared absorption method, the nitrogen content (N) using a gas fusion-thermal conductivity method, and the carbon content (C) using a combustion-infrared absorption method, all using a gas analyzer. The components of the RTB-based sintered magnet material may not add up to 100 mass%. This is due to the different measurement methods mentioned above and the possible inclusion of other elements as unavoidable impurities. Note that TRE is the total value of Nd and Pr.

[0045] [Table 1]

[0046] [Preparing RM alloys] Each element was weighed so as to obtain the composition of the RM-based alloy (excluding O, N, and C) shown in No. A of Table 2, and the raw materials were melted and subjected to single-roll rapid cooling to obtain a ribbon-shaped alloy. The composition of the obtained RM-based alloy is shown in Table 2. The Pr and Cu contents in Table 2 were measured using high-frequency inductively coupled plasma atomic emission spectroscopy, while the oxygen content (O) was measured using gas fusion-infrared absorption spectroscopy, the nitrogen content (N) was measured using gas fusion-thermal conductivity spectroscopy, and the carbon content (C) was measured using a gas analyzer using combustion-infrared absorption spectroscopy.

[0047] [Table 2]

[0048] [Diffusion process] The RTB-based sintered magnet materials Nos. 1 to 7 in Table 1 were cut and machined into 7.2 mm cubes. After machining, PVA (polyvinyl alcohol) was applied as an adhesive to the entire surface of the RTB-based sintered magnet material using a dipping method. Next, an RM-based alloy was attached to the entire surface of the adhesive-coated RTB-based sintered magnet material under the manufacturing conditions shown in Table 3. The amount of RM-based alloy attached was adjusted by crushing the ribbon-shaped RM-based alloy in a mortar in an argon atmosphere, passing it through several sieves with mesh sizes ranging from 45 to 1000 μm, and mixing it with RM-based alloy powders of different particle sizes. The amount of attachment was approximately 3 mass%. The RTB-based sintered magnet material with the RM-based alloy attached was then inserted into a heat treatment furnace for the diffusion process. The argon flow rate and the vacuum pump displacement were controlled to set the furnace pressure shown in Table 3, and the RTB-based sintered magnet material with the RM-based alloy attached was then heated under the heat treatment conditions shown in Table 3. The heat treatment furnace used was a vertical vacuum pressure sintering and rapid cooling furnace PVSGgr30 / 30 manufactured by Shimadzu Corporation, and the argon used had a purity of 99.99% by volume. After heating under the diffusion process conditions shown in Table 3, argon was introduced until the pressure inside the furnace reached 600,000 Pa (600 kPa), and then the material was cooled.

[0049] The RTB sintered magnet materials heated in the diffusion step were subjected to a second heat treatment in which they were heated to 480°C in a vacuum heat treatment furnace in a reduced-pressure argon atmosphere controlled at 100 Pa. After the second heat treatment, each sample was machined on its entire surface using a surface grinder to obtain cubic samples (RTB sintered magnets) measuring 7.0 mm x 7.0 mm x 7.0 mm. The heating temperature in the diffusion step and the heating temperature of the RTB sintered magnets in the step of carrying out the heat treatment after the diffusion step were each measured using a thermocouple.

[0050] [Table 3]

[0051] [Sample evaluation] The samples prepared under the conditions listed in Table 3 were measured using a BH tracer to measure the residual magnetic flux density Br and coercive force H cJ The coercive force H of samples No. 1-1 to 3-2 was measured. cJ The relationship between the coercive force H and the furnace pressure is shown in Figure 2. In the comparative example (No. 1-1) where the heat treatment was performed under the condition of a low furnace pressure of 6 Pa, the coercive force H cJ In contrast, in the example of the present invention (No. 1-2) which was heat-treated at a high furnace pressure of 600,000 Pa (600 kPa), the coercive force H cJ Similarly, in the comparative example (No. 2-1) which was heat-treated under the condition of a low furnace pressure of 6 Pa, the coercive force H cJ In contrast, in the example of the present invention (No. 2-2) that was heat-treated at a high furnace pressure of 600,000 Pa (600 kPa), the coercive force H cJ Furthermore, in the comparative example (No. 3-1) where the heat treatment was performed under the condition of a low furnace pressure of 6 Pa, the coercive force H cJ In contrast, in the example of the present invention (No. 3-2) that was heat-treated at a high furnace pressure of 600,000 Pa (600 kPa), the coercive force H cJ In both cases, the coercive force H cJ had improved greatly.

[0052] The samples prepared under the conditions listed in Table 3 were measured using a BH tracer to measure the residual magnetic flux density B r and coercive force H cJ The coercive force H of samples No. 4-1 to 5-5 was measured. cJ The relationship between the coercive force H and the furnace pressure is shown in Figure 3. In the comparative example (No. 4-1) where the heat treatment was performed under the condition of a low furnace pressure of 40 Pa, cJ In contrast, in the inventive examples (Nos. 4-2, 4-3, 4-4, and 4-5) that were heat-treated under conditions where the furnace pressure was 10,000 Pa (10 kPa) or higher, the coercive force H cJSimilarly, in the comparative example (No. 5-1) that was heat-treated under a low furnace pressure of 40 Pa, the coercive force H cJ In contrast, in the inventive examples (Nos. 5-2, 5-3, 5-4, and 5-5) that were heat-treated under conditions where the furnace pressure was 10,000 Pa (10 kPa) or higher, the coercive force H cJ In all cases, the coercive force H cJ had improved greatly.

[0053] The samples prepared under the conditions listed in Table 3 were measured using a BH tracer to measure the residual magnetic flux density B r and coercive force H cJ The coercive force H of samples No. 6-1 to 7-5 was measured. cJ The relationship between the coercive force H and the furnace pressure is shown in Figure 4. In the comparative example (No. 6-1) that was heat-treated under the condition of a low furnace pressure of 40 Pa, cJ In contrast, in the inventive examples (Nos. 6-2, 6-3, 6-4, and 6-5) that were heat-treated under conditions where the furnace pressure was 10,000 Pa (10 kPa) or higher, the coercive force H cJ Similarly, in the comparative example (No. 7-1) that was heat-treated under a low furnace pressure of 40 Pa, the coercive force H cJ In contrast, in the inventive examples (Nos. 7-2, 7-3, 7-4, and 7-5) that were heat-treated under the condition of a furnace pressure of 10,000 Pa (10 kPa) or more, the coercive force H cJIn all cases, the coercive force H cJ had improved greatly. [Example]

[0054] [Preparing RTB sintered magnet material] Each element was weighed to obtain the composition of the RTB based sintered magnet material shown in Table 4 (excluding O, N, and C), and an RTB based sintered magnet material was obtained in the same manner as in Example 1. The density of the obtained RTB based sintered magnet material was 7.5 Mg / m 3 The components of the resulting RTB based sintered magnet material were measured in the same manner as in Example 1.

[0055] [Table 4]

[0056] [Preparing RM alloys] Each element was weighed so as to obtain the composition of the RM-based alloy (excluding O, N, and C) shown in No. B of Table 5, and a ribbon-shaped alloy was obtained in the same manner as in Example 1. The composition of the obtained RM-based alloy is shown in Table 5. The contents of Pr, Tb, Cu, and Ga, as well as the amount of oxygen (O), the amount of nitrogen (N), and the amount of carbon (C) in Table 5 were measured in the same manner as in Example 1.

[0057] [Table 5]

[0058] [Diffusion process] The RTB sintered magnet materials Nos. 8 to 12 in Table 4 and the RM alloys in Table 5 were subjected to a diffusion process similar to that of Example 1 under the production conditions shown in Table 6. As shown in Table 6, the deposition amounts were each around 2 mass%. The RTB sintered magnet materials with the RM alloys deposited were placed in a heat treatment furnace for the diffusion process, and the argon flow rate and the vacuum pump exhaust rate were controlled to set the furnace pressure shown in Table 6. The RTB sintered magnet materials with the RM alloys deposited were then heated under the heat treatment conditions shown in the diffusion process. After heating under the diffusion process conditions shown in Table 6, argon was introduced until the furnace pressure reached 600,000 Pa (600 kPa), and the material was then cooled.

[0059] The RTB sintered magnet materials heated in the diffusion step were subjected to a second heat treatment in which they were heated to 480°C in a vacuum heat treatment furnace in a reduced-pressure argon atmosphere controlled at 100 Pa. After the second heat treatment, each sample was machined on its entire surface using a surface grinder to obtain cubic samples (RTB sintered magnets) measuring 7.0 mm x 7.0 mm x 7.0 mm. The heating temperature in the diffusion step and the heating temperature of the RTB sintered magnets in the step of carrying out the heat treatment after the diffusion step were each measured using a thermocouple.

[0060] [Table 6]

[0061] [Sample evaluation] The samples prepared under the conditions listed in Table 6 were measured using a BH tracer to measure the residual magnetic flux density B r and coercive force H cJ The coercive force H of samples No. 8-1 to 10-4 was measured. cJ The relationship between the coercive force H and the furnace pressure is shown in Figure 5. In the comparative example (No. 8-1) that was heat-treated under the condition of a low furnace pressure of 45 Pa, cJ In contrast, in the inventive examples (Nos. 8-2, 8-3, and 8-4) that were heat-treated under conditions where the furnace pressure was 10,000 Pa (10 kPa) or higher, the coercive force H cJSimilarly, in the comparative example (No. 9-1) that was heat-treated under a low furnace pressure of 45 Pa, the coercive force H cJ In contrast, in the inventive examples (Nos. 9-2, 9-3, and 9-4) that were heat-treated under the condition of a furnace pressure of 10,000 Pa (10 kPa) or more, the coercive force H cJ Furthermore, in the comparative example (No. 10-1) that was heat-treated under a low furnace pressure of 45 Pa, the coercive force H cJ In contrast, in the inventive examples (Nos. 10-2, 10-3, and 10-4) that were heat-treated under conditions where the furnace pressure was 10,000 Pa (10 kPa) or higher, the coercive force H cJ In all cases, the coercive force H cJ had improved greatly.

[0062] The samples prepared under the conditions listed in Table 6 were measured using a BH tracer to measure the residual magnetic flux density B r and coercive force H cJ The coercive force H of samples No. 11-1 to 12-4 was measured. cJ The relationship between the coercive force H and the furnace pressure is shown in Figure 6. In the comparative example (No. 11-1) where the heat treatment was performed under the condition of a low furnace pressure of 45 Pa, cJ In contrast, in the inventive examples (Nos. 11-2, 11-3, and 11-4) that were heat-treated under the condition of a furnace pressure of 10,000 Pa (10 kPa) or more, the coercive force H cJ Similarly, in the comparative example (No. 12-1) that was heat-treated under a low furnace pressure of 45 Pa, the coercive force H cJIn contrast, in the inventive examples (Nos. 12-2, 12-3, and 12-4) that were heat-treated under the condition of a furnace pressure of 10,000 Pa (10 kPa) or more, the coercive force H cJ In all cases, the coercive force H cJ had improved greatly.

[0063] From the above results, it can be seen that, according to the method for producing an RTB based sintered magnet of the present disclosure, by carrying out the diffusion step in an inert gas atmosphere of 10 kPa or more, the H cJ Therefore, the H content can be improved to the same extent as that of RTB sintered magnets obtained by the conventional diffusion method. cJ It was found that the amount of heavy rare earth element RH used could be reduced when compared.

Claims

1. a sintered magnet material preparation step of preparing an R-T-B based sintered magnet material (R is a rare earth element, T is Fe or Fe and Co, and B is boron); a diffusion source preparation step of preparing a diffusion source powder formed from an alloy containing a rare earth element; an adhering step of adhering the diffusion source powder to the surface of the sintered RTB based magnet material; a heat treatment step of heat treating the sintered RTB based magnet material to which the diffusion source powder has adhered at a temperature equal to or lower than the sintering temperature of the sintered RTB based magnet material; Including, The heat treatment step is carried out in an inert gas atmosphere of 10 kPa or more. A method for producing an RTB based sintered magnet.

2. 2. The method for producing a sintered RTB based magnet according to claim 1, wherein the diffusion source powder contains at least Pr and / or Nd as a rare earth element.

3. 3. The method for producing a sintered RTB based magnet according to claim 2, wherein the diffusion source powder contains a metal element other than a rare earth element.

4. 4. The method for producing a sintered R-T-B based magnet according to claim 3, wherein the metal element other than rare earth elements is at least one selected from the group consisting of Al, Cu, Zn, Ga, Fe, Co, and Ni.

5. 2. The method for producing a sintered RTB based magnet according to claim 1, wherein in the adhering step, an adhesive is applied to the surface of the sintered RTB based magnet material, and the diffusion source powder is adhered to the adhesive.

6. 2. The method for producing a sintered RTB based magnet according to claim 1, wherein in the heat treatment step, an inert gas atmosphere of 10 kPa or more is maintained from before the heat treatment until the end of the heat treatment.

7. 2. The method for producing a sintered RTB based magnet according to claim 1, wherein the temperature of the heat treatment step is equal to or higher than the melting point of the diffusion source powder.

8. 8. The method for producing a sintered RTB based magnet according to claim 7, wherein the heat treatment temperature in the heat treatment step is 500° C. or higher and 1000° C. or lower.

9. In the sintered magnet material preparation step, the atomic ratio of B to T in the R-T-B based sintered magnet material is R ２ T １４ 9. The method for producing a sintered RTB based magnet according to claim 1, wherein the atomic ratio of B to T is lower than that in the stoichiometric composition of the B compound.

10. 10. The method for producing a sintered RTB based magnet according to claim 9, wherein the B content in the sintered RTB based magnet material is 0.80 mass% or more and 0.99 mass% or less in the sintered magnet material preparation step.

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