RTB-based permanent magnets and motors

Abstract

To provide an R-T-B based permanent magnet which is high in both of a residual magnetic flux density Br at a room temperature and a coercive force HcJ at a high temperature.SOLUTION: An R-T-B based permanent magnet comprises R as a rare earth element, T of an iron group element, and B of boron, in which R includes a light rare earth element and a heavy rare earth element. The R-T-B based permanent magnet further comprises Al, Ga and Zr. To 100 mass% of the R-T-B based permanent magnet, the total content of R is 28.50-30.25 mass% (exclusive of 28.50 mass%), the content of B is 0.93-0.98 mass%, the content of Al is 0.03-0.19 mass%, the content of Ga is 0.03-0.15 mass%, and the content of Zr is 0.30-0.50 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an RTB-based permanent magnet and a motor. [Background technology]

[0002] Patent Document 1 discloses an RTB permanent magnet with high remanence and coercive force at room temperature. The RTB permanent magnet described in Patent Document 1 has improved coercive force by diffusing heavy rare earth elements into grain boundaries. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-93202 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an RTB permanent magnet that has both a high remanence Br at room temperature and a high coercive force HcJ at high temperatures. [Means for solving the problem]

[0005] In order to achieve the above object, the RTB permanent magnet of the present invention has the following features: An RTB-based permanent magnet in which R is a rare earth element, T is an iron-group element, and B is boron, and R contains a light rare earth element and a heavy rare earth element, The RTB permanent magnet further contains Al, Ga, and Zr, The RTB permanent magnet is taken as 100% by mass, The total content of R is 28.50 mass% to 30.25 mass% (excluding 28.50 mass%), The content of B is 0.93 mass% to 0.98 mass%; The Al content is 0.03 mass% to 0.19 mass%; The content of Ga is 0.03% to 0.15% by mass, The content of Zr is 0.30% to 0.50% by mass, which is characterized.

[0006] Due to having the above characteristics, the R-T-B-based permanent magnet of the present invention becomes an R-T-B-based permanent magnet with both a high residual magnetic flux density Br and a coercive force HcJ at high temperatures.

[0007] The total content of light rare earth elements may be 28.50% to 29.50% by mass, and the total content of heavy rare earth elements may be 0% to 0.75% by mass (excluding 0%).

[0008] It may contain Pr, and the content of Pr may be 0.01% to 1.00% by mass.

[0009] It may not substantially contain Pr.

[0010] It may have a concentration gradient of heavy rare earth elements that decreases from the magnet surface toward the inside.

[0011] The motor of the present invention includes the above R-T-B-based permanent magnet.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic diagram of an R-T-B-based permanent magnet.

Modes for Carrying Out the Invention

[0016] R is classified as light rare earth elements (RL) and heavy rare earth elements (RH). In RTB permanent magnets, RL is scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), and europium (Eu), while RH is gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). RTB permanent magnets contain both RL and RH as R.

[0017] R may be one or more selected from Nd and Pr, and one or more selected from Dy and Tb.

[0018] The RTB permanent magnet may contain at least Nd and Tb as R.

[0019] T is an iron group element. The RTB permanent magnet may contain at least Fe as T. The RTB permanent magnet may contain Fe alone or Fe and Co as T.

[0020] A portion of the boron contained in the B site of the RTB permanent magnet may be substituted with carbon (C).

[0021] The R content (TRE) in the RTB permanent magnet is 28.50% by mass to 30.25% by mass (excluding 28.50% by mass) based on 100% by mass of the RTB permanent magnet. It may be 28.84% by mass to 29.81% by mass, or 29.14% by mass to 29.41% by mass. If the TRE content is too low, the sinterability tends to decrease. If the TRE content is too high, the Br tends to decrease.

[0022] There are no particular restrictions on the RL content (TRL) in the RTB permanent magnet, but it may be 28.50 mass % to 29.50 mass % or 28.84 mass % to 29.11 mass % with the RTB permanent magnet being 100 mass %.

[0023] The RTB permanent magnet may contain Pr as R. The Pr content may be 0.00% to 10.00% by mass, with the RTB permanent magnet being 100% by mass.

[0024] The Pr content may be 0.01% to 1.00% by mass, with the RTB permanent magnet being 100% by mass. When the Pr content is within the above range, HcJ at room temperature and HcJ at high temperatures are more likely to be improved compared to when Pr is substantially not contained. Furthermore, Br and HcJ at high temperatures are more likely to be improved compared to when the Pr content is high.

[0025] The RTB permanent magnet may be substantially free of Pr. "Substantially free" means that the content is less than 0.01% by mass, with the RTB permanent magnet being 100% by mass. When the magnet is substantially free of Pr, the Br is more likely to be improved compared to when Pr is included.

[0026] The Pr content may be 5.00% to 10.00% by mass, with the RTB permanent magnet being 100% by mass. When the Pr content is within the above range, HcJ at room temperature is more likely to be improved compared to when the Pr content is low.

[0027] There are no particular restrictions on the RH content (TRH) in an RTB permanent magnet, but it may be 0% to 0.75% by mass (excluding 0% by mass) or 0.30% to 0.75% by mass, taking the RTB permanent magnet as 100% by mass. RH may consist essentially of Tb alone. The lower the TRH, the more likely Br is to improve, and the higher the TRH, the more likely HcJ is to improve. RH is expensive, so the lower the TRH, the easier it is to produce an RTB permanent magnet at low cost.

[0028] The Co content may be 0.30% by mass to 3.0% by mass, with the mass of the entire RTB permanent magnet being 100% by mass. An RTB permanent magnet with high corrosion resistance can be obtained even with a low content of expensive Co. As a result, it becomes easier to manufacture highly corrosion-resistant RTB permanent magnets at low cost. If the Co content is too low, corrosion resistance is likely to decrease. If the Co content is too high, the effect of improving corrosion resistance will plateau and costs will increase.

[0029] The content of Fe is the substantial balance of the RTB permanent magnet. "Substantial balance" means the balance excluding the aforementioned R and Co, and the below-described B, Al, Ga, Zr, Mn, Cu, and other elements.

[0030] The B content in an RTB permanent magnet is 0.93 to 0.98 mass %, taking the RTB permanent magnet as 100 mass %. If the B content is too much or too little, the HcJ at high temperatures tends to decrease.

[0031] The RTB permanent magnet further contains Al, Ga, and Zr. When Al, Ga, and Zr are contained within the respective content ranges shown below, the following excellent effects can be obtained.

[0032] The Al content is 0.03% to 0.19% by mass, with the RTB permanent magnet being 100% by mass. The Al content may be 0.05% to 0.10% by mass, or may be 0.05% to 0.09% by mass. If the Al content is too low, HcJ at high temperatures tends to decrease. If the Al content is too high, Br tends to decrease.

[0033] The Ga content is 0.03% to 0.15% by mass, with the RTB permanent magnet being 100% by mass. The Ga content may be 0.06% to 0.10% by mass. If the Ga content is too low, HcJ at high temperatures tends to decrease. If the Ga content is too high, Br and HcJ at high temperatures tend to decrease.

[0034] The Zr content is 0.30% by mass to 0.50% by mass, with the RTB permanent magnet being 100% by mass. If the Zr content is too low, HcJ at high temperatures tends to decrease. If the Zr content is too high, Br and HcJ at high temperatures tend to decrease.

[0035] The RTB permanent magnet may further contain Mn and / or Cu.

[0036] There are no particular restrictions on the Mn content, and Mn need not be contained. When Mn is contained, the Mn content may be 0.02 mass % to 0.10 mass %. When the Mn content is within the above range, Br and HcJ at high temperatures tend to be improved.

[0037] There are no particular restrictions on the Cu content, and Cu need not be contained. When Cu is contained, the Cu content may be 0.10 mass % to 0.55 mass %. When the Cu content is within the above range, Br and HcJ at high temperatures tend to be improved.

[0038] The RTB permanent magnet may contain elements other than the above-mentioned R, T, B, Al, Ga, Zr, Mn, and Cu as other elements. There are no particular restrictions on the content of these other elements, as long as they do not significantly affect the magnetic properties of the RTB permanent magnet. For example, the total content of these other elements may be 1.0 mass% or less, assuming the RTB permanent magnet to be 100 mass%. The total content of rare earth elements other than Nd, Pr, Dy, and Tb may be 0.3 mass% or less.

[0039] The contents of C, nitrogen (N) and oxygen (O) will be described below as examples of other elements.

[0040] The C content of an RTB permanent magnet may be 600 ppm to 1100 ppm relative to the RTB permanent magnet. By setting the C content to 1100 ppm or less, HcJ tends to be improved. Furthermore, producing an RTB permanent magnet with a C content of less than 600 ppm places a heavy burden on the process. Therefore, it is difficult to produce an RTB permanent magnet with a C content of less than 600 ppm at low cost.

[0041] The N content of an RTB permanent magnet may be 250 ppm to 700 ppm relative to the RTB permanent magnet. By setting the N content to 700 ppm or less, HcJ tends to be improved. Furthermore, producing an RTB permanent magnet with an N content of less than 250 ppm places a heavy burden on the process. Therefore, it is difficult to produce an RTB permanent magnet with an N content of less than 250 ppm at low cost.

[0042] The O content of an RTB permanent magnet may be 350 ppm to 1000 ppm relative to the RTB permanent magnet. Manufacturing an RTB permanent magnet with an O content of less than 350 ppm places a heavy burden on the process. Therefore, it is difficult to manufacture an RTB permanent magnet with an O content of less than 350 ppm at low cost.

[0043] The various components contained in RTB permanent magnets can be measured by conventionally known methods. The amounts of various elements are measured, for example, by X-ray fluorescence analysis and inductively coupled plasma atomic emission spectrometry (ICP analysis). The O content is measured, for example, by inert gas fusion-nondispersive infrared absorption spectrometry. The C content is measured, for example, by oxygen flow combustion-infrared absorption spectrometry. The N content is measured, for example, by inert gas fusion-thermal conductivity spectrometry.

[0044] In particular, when the Al content is 0.05 mass% to 0.09 mass%, The R content (TRE) is 28.50 mass% to 30.25 mass% (excluding 28.50 mass%), RL content (TRL) is 28.50 mass% to 29.81 mass%; The RH content (TRH) is 0 mass% to 0.75 mass% (excluding 0 mass%), Co content is 0.30 mass% to 3.00 mass%; The content of B is 0.93 mass% to 0.98 mass%; The Ga content is 0.03 mass% to 0.15 mass%; Zr content is 0.30 mass% to 0.50 mass%; The Mn content is 0.02 mass% to 0.10 mass%; The Cu content may be 0.10 mass % to 0.55 mass %.

[0045] When the Al content is 0.05 mass% to 0.09 mass%, C content is 600ppm to 1000ppm, N content is 250 ppm to 700 ppm, The O content may be 350 ppm to 1000 ppm.

[0046] There are no particular limitations on the shape of the RTB permanent magnet, and examples include a rectangular parallelepiped shape.

[0047] The RTB permanent magnet may have a concentration gradient in which the concentration of RH decreases from the outside to the inside of the RTB permanent magnet 1. There are no particular restrictions on the type of RH that has the concentration gradient. For example, it may be Dy and / or Tb, or it may be Tb.

[0048] Specifically, as shown in FIG. 1, the rectangular parallelepiped RTB permanent magnet 1 has a surface portion and a center portion, and the RH content in the surface portion can be 2% or more, 5% or more, or 10% or more higher than the RH content in the center portion. The surface portion refers to the surface of the RTB permanent magnet 1. For example, POINTS C and C' in FIG. 1 (the centers of gravity of the opposing surfaces in FIG. 1) are surface portions. The center portion refers to the center of the RTB permanent magnet 1. For example, it refers to a portion halfway through the thickness of the RTB permanent magnet 1. For example, POINT M in FIG. 1 (the midpoint between POINT C and POINT C') is the center portion. POINTS C and C' in FIG. 1 may also be the center of gravity of the surface with the largest area among the surfaces of the RTB permanent magnet 1, and the center of gravity of the surface facing that surface.

[0049] There are no particular limitations on the method for forming the aforementioned RH concentration gradient in an RTB permanent magnet. For example, a RH concentration gradient can be formed in the RTB permanent magnet by grain boundary diffusion of RH, which will be described later.

[0050] Furthermore, the main phase particles of the RTB permanent magnet may be core-shell particles consisting of a core and a shell covering the core. At least the shell may contain RH, Dy or Tb, or Tb.

[0051] By having RH present in the shell, the magnetic properties of the RTB-based permanent magnet can be efficiently improved.

[0052] The portion where the molar ratio of RH to RL (RH / RL) is at least twice the RH / RL at the center (core) of the main phase particle is defined as the shell.

[0053] There is no particular limitation on the thickness of the shell, but it may be 500 nm or less on average. There is also no particular limitation on the particle size of the main phase particles, but it may be 1.0 μm or more and 6.5 μm or less on average.

[0054] There are no particular limitations on the method for converting the main phase particles into the core-shell particles. For example, there is a method using grain boundary diffusion, which will be described later. RH diffuses into the grain boundaries and replaces R on the surface of the main phase particles, forming a shell with a high RH content, resulting in the core-shell particles.

[0055] The method for producing an RTB permanent magnet will be described in detail below, but the method for producing an RTB permanent magnet is not limited to this, and other known methods may also be used.

[0056] [Raw powder preparation process] The raw material powder can be prepared by a known method. Hereinafter, the case of the one-alloy method in which a single alloy is used as the raw material powder will be described, but the so-called two-alloy method in which two or more alloys with different compositions are mixed to prepare the raw material powder may also be used.

[0057] First, a raw material alloy for the RTB permanent magnet is prepared (alloy preparation step). In the alloy preparation step, raw material metals corresponding to the composition of the RTB permanent magnet are melted by a known method, and then cast to produce a raw material alloy having the desired composition.

[0058] As the raw material metal, for example, simple R, simple metal elements such as Fe, Co, and Cu, alloys consisting of multiple elements (e.g., Fe-Co alloys), or compounds consisting of multiple elements (e.g., ferroboron) can be used as appropriate. There are no particular limitations on the casting method used to cast the raw material alloy from the raw material metal. Strip casting may be used to obtain an RTB-based permanent magnet with high magnetic properties. The obtained raw material alloy may be subjected to a homogenization treatment using a known method, as necessary.

[0059] After the raw alloy is prepared, it is pulverized (pulverization step). The atmosphere in each step from the pulverization step to the sintering step can have a low oxygen concentration in order to obtain high magnetic properties. For example, the oxygen concentration in the atmosphere in each step can be set to 200 ppm or less. By controlling the oxygen concentration in the atmosphere in each step, the O content in the RTB permanent magnet can be controlled.

[0060] The following describes a case where the pulverization step is carried out in two stages: a coarse pulverization step in which the particles are pulverized until the particle size is about several hundred μm to several mm, and a fine pulverization step in which the particles are pulverized until the particle size is about several μm. However, the pulverization step may also be carried out in a single stage consisting of only the fine pulverization step.

[0061] In the coarse pulverization step, the material is coarsely pulverized until the particle size is on the order of several hundred μm to several mm. This produces a coarsely pulverized powder. There are no particular limitations on the coarse pulverization method, and it can be performed by any known method, such as a hydrogen absorption pulverization method or a method using a coarse pulverizer. When hydrogen absorption pulverization is performed, the N content in the RTB permanent magnet can be controlled by controlling the nitrogen gas concentration in the atmosphere during the dehydrogenation treatment.

[0062] Next, the obtained coarsely pulverized powder is finely pulverized until the average particle size is about several μm (fine pulverization step). This results in a finely pulverized powder (raw material powder). The average particle size of the finely pulverized powder may be 1 μm or more and 10 μm or less, 2 μm or more and 6 μm or less, or 2 μm or more and 4 μm or less. By controlling the nitrogen gas concentration in the atmosphere during the fine pulverization step, the N content in the RTB permanent magnet can be controlled.

[0063] There are no particular limitations on the method of pulverization, and it can be carried out, for example, by using various pulverizers.

[0064] When the coarsely pulverized powder is finely pulverized, various grinding aids such as lauric acid amide and oleic acid amide can be added to obtain a finely pulverized powder in which the crystal grains tend to orient in a specific direction when compacted under pressure in a magnetic field. Furthermore, by changing the amount of grinding aid added, the C content in the RTB permanent magnet can be controlled.

[0065] [Molding process] In the compacting process, the finely pulverized powder is molded into the desired shape. There are no particular limitations on the molding method. For example, the finely pulverized powder is filled into a mold and pressed in a magnetic field. The resulting compact has crystal grains oriented in a specific direction. This results in an RTB-based permanent magnet with a higher Br.

[0066] The pressure applied during molding can be 20 MPa or more and 300 MPa or less. The magnetic field applied can be 950 kA / m or more, or 950 kA / m or more and 1600 kA / m or less. The magnetic field applied is not limited to a static magnetic field, but can also be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

[0067] As a molding method, in addition to the dry molding in which the finely pulverized powder is molded as is as described above, wet molding in which a slurry in which the finely pulverized powder is dispersed in a solvent such as oil can also be applied.

[0068] There are no particular limitations on the shape of the compact obtained by compacting the finely pulverized powder. The density of the compact at this stage is 3.7 Mg / m 3 ~4.5Mg / m 3 It can be said that:

[0069] [Sintering process] The sintering process is a process in which a compact is sintered in a vacuum or in an inert gas atmosphere to obtain a sintered body. The sintering conditions must be adjusted depending on various factors, such as the composition, pulverization method, average particle size and particle size distribution. For example, the compact is sintered by heating it in a vacuum or in an inert gas atmosphere at a temperature between 1000°C and 1200°C for 1 hour to 20 hours. Sintering under the above sintering conditions can produce a high-density sintered body. At least 7.45 Mg / m 3 The density of the sintered body is 7.50 Mg / m 3 The density of the sintered body is equivalent to the density of the RTB permanent magnet after the grain boundary diffusion process described below.

[0070] [Aging treatment process] The aging treatment step is a step of heat treating (aging treatment) the sintered body at a temperature lower than the sintering temperature. There is no particular restriction on whether or not aging treatment is performed, and there is no particular restriction on the number of times aging treatment is performed, and it is performed appropriately depending on the desired magnetic properties. In addition, the grain boundary diffusion step described below may also serve as the aging treatment step. Below, we will explain the case where aging treatment is performed twice.

[0071] The first aging step is referred to as the first aging step, the second aging step is referred to as the second aging step, the aging temperature of the first aging step is referred to as T1, and the aging temperature of the second aging step is referred to as T2.

[0072] There are no particular limitations on T1 and the aging time in the primary aging step. T1 can be 700° C. or higher and 900° C. or lower. The aging time can be 1 hour or higher and 10 hours or lower.

[0073] There are no particular limitations on T2 and the aging time in the second aging step. T2 can be set to 450° C. or higher and 700° C. or lower. The aging time can be set to 1 hour or higher and 10 hours or lower.

[0074] Such an aging treatment can improve the magnetic properties, particularly the HcJ, of the finally obtained RTB permanent magnet.

[0075] [Processing process (before grain boundary diffusion)] If necessary, a step of processing the sintered body into a desired shape may be included, for example, by shaping such as cutting or grinding, or by chamfering such as barrel polishing.

[0076] [Grain boundary diffusion process] The grain boundary diffusion process can be carried out by adhering a diffusing material to the surface of the sintered body and heating the sintered body with the diffusing material attached. This results in an RTB-based permanent magnet with improved HcJ. There are no particular restrictions on the type of diffusing material. The diffusing material may contain RH (e.g., Tb and / or Dy), or may contain all of the first to third components listed below. The first component is a hydride of Tb and / or a hydride of Dy. The second component is a hydride of Nd and / or a hydride of Pr. The third component is simple Cu, an alloy containing Cu, and / or a compound containing Cu.

[0077] The Nd and / or Pr contained in the second component and the Cu contained in the third component have lower melting points than the Tb and / or Dy contained in the first component. Therefore, the second and third components diffuse to grain boundaries, particularly two-particle boundaries (grain boundaries between two main-phase particles), before the first component. The first diffusion of the second and third components to the two-particle boundaries facilitates the first component to diffuse further to the two-particle boundaries. Therefore, compared with a case where the diffusion material contains only the first component, a diffusion material containing all of the first to third components can diffuse Tb and / or Dy to the two-particle boundaries at a lower temperature and in a shorter time. As a result, the temperature and time required for diffusion of Tb and / or Dy can be lowered and the diffusion time can be shortened, compared with a case where the diffusion material contains only the first component. Consequently, excessive diffusion of Tb and / or Dy into the main-phase particles is suppressed. In addition, when the diffusion material contains both the second component and the third component together with the first component, Tb and / or Dy are more likely to diffuse into the two-particle grain boundary than when the diffusion material contains only one of the second component and the third component together with the first component.

[0078] The diffusing material may be a slurry containing a solvent in addition to the first to third components. The solvent contained in the slurry may be a solvent other than water. For example, it may be an organic solvent such as alcohol, aldehyde, or ketone. Furthermore, the diffusing material may contain a binder. There are no particular restrictions on the type of binder. For example, a resin such as an acrylic resin may be contained as the binder. By containing a binder, the diffusing material is more likely to adhere to the surface of the sintered body.

[0079] The diffusion material may be a paste containing a solvent and a binder in addition to the first to third components. The paste has fluidity and high viscosity. The viscosity of the paste is higher than that of a slurry.

[0080] Before the grain boundary diffusion, the sintered body to which the slurry or paste has been applied may be dried to remove the solvent.

[0081] The diffusion treatment temperature in the grain boundary diffusion step may be 800°C or higher and 950°C or lower. In the grain boundary diffusion step, the rate of temperature increase from a temperature lower than the diffusion treatment temperature (for example, about 500°C) to the diffusion temperature may be slowed. In this case, in a temperature range of about 600°C, Nd and / or Pr contained in the main phase particles tend to seep into the grain boundaries and form Nd-rich and / or Pr-rich liquid phases. As a result, in a temperature range of about 800°C, dissolution of the first component, Tb hydride and / or Dy hydride, tends to proceed easily.

[0082] The diffusion treatment time is defined as the time during which the sintered body is maintained at the diffusion treatment temperature, and may be 1 hour or more and 50 hours or less. The atmosphere in the grain boundary diffusion step may be a non-oxidizing atmosphere, for example, a rare gas atmosphere such as argon. The grain boundary diffusion step may also serve as the above-mentioned aging treatment step.

[0083] Furthermore, after the diffusion treatment, a further heat treatment may be performed. In this case, the heat treatment temperature may be 450°C or higher and 600°C or lower. The heat treatment time may be 1 hour or higher and 10 hours or lower. By performing such a heat treatment, the magnetic properties, particularly the HcJ, of the finally obtained RTB-based permanent magnet can be improved.

[0084] [Processing process (after grain boundary diffusion)] After the grain boundary diffusion step, polishing may be performed to remove any remaining diffusion material from the surface of the RTB permanent magnet. The RTB permanent magnet may also be subjected to other processing, such as shaping such as cutting or grinding, or chamfering such as barrel polishing.

[0085] In the above manufacturing method, processing steps are performed before and after grain boundary diffusion, but these steps are not necessarily required. The grain boundary diffusion step may also serve as an aging step. There are no particular limitations on the heating temperature when the grain boundary diffusion step also serves as an aging step. It is particularly preferable to perform the aging step at a temperature that is both preferred for the grain boundary diffusion step and also preferred for the aging step.

[0086] In particular, an RTB permanent magnet after grain boundary diffusion tends to have a concentration gradient in which the RH concentration decreases from the outside to the inside of the RTB permanent magnet. Furthermore, the main phase particles contained in the RTB permanent magnet after grain boundary diffusion tend to have the above-mentioned core-shell structure.

[0087] The RTB permanent magnets obtained in this manner have desirable properties, specifically, excellent Br and HcJ at high temperatures.

[0088] The RTB permanent magnet obtained by the above method becomes a magnetic RTB permanent magnet by being magnetized.

[0089] The RTB permanent magnets described above are suitable for use in motors, generators, etc. They are particularly suitable for use in motors that are driven at high currents and high frequencies.

[0090] When conventional RTB permanent magnets are used in motors driven by high currents and high frequencies, they may be exposed to high temperatures or may generate heat themselves. As a result, HcJ decreases, making them more susceptible to demagnetization due to demagnetizing fields. Furthermore, RTB permanent magnets with high HcJ at room temperature tend to have low Br.

[0091] When the above-mentioned RTB permanent magnets are used in motors driven at high currents and high frequencies, even when the RTB permanent magnets are subjected to high temperatures or when the RTB permanent magnets themselves generate heat, their high HcJ at high temperatures makes them less susceptible to demagnetization due to demagnetizing fields. Furthermore, their high Br increases the maximum energy product at high temperatures. Therefore, motors incorporating the above-mentioned RTB permanent magnets can produce high output, especially when driven at high currents and high frequencies.

[0092] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention.

[0093] The method for producing an RTB permanent magnet is not limited to the above method and may be modified as appropriate. For example, although the above method for producing an RTB permanent magnet is a production method by sintering, the RTB permanent magnet may also be produced by hot working. The method for producing an RTB permanent magnet by hot working includes the following steps. (a) Melting and quenching process in which raw metal is melted and the resulting molten metal is quenched to obtain a thin ribbon. (b) A crushing process in which the ribbon is crushed to obtain a flake-shaped raw powder. (c) Cold compaction process in which the crushed raw material powder is cold compacted (d) a preheating step for preheating the cold-formed body (e) A hot forming process in which the preheated cold-formed body is hot-formed. (f) A hot plastic working process in which the hot-formed body is plastically deformed into a predetermined shape. (g) Aging treatment process for aging RTB permanent magnets The steps after the aging treatment are the same as those in the case of production by sintering. [Example]

[0094] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[0095] (Production of RTB-based permanent magnets) Raw material alloys were prepared using the strip casting method so that the final RTB permanent magnets would have the composition of each sample shown in Tables 1 and 2. Elements not listed in Tables 1 and 2, such as H, Si, Ca, La, Ce, and Cr, may be detected in the final RTB permanent magnets. Si is mainly mixed in from the ferroboron raw material and the crucible used when melting the alloy. Ca, La, and Ce are mixed in from the rare earth raw material. Cr may also be mixed in from the electrolytic iron. In Tables 1 and 2, the Fe content is listed as Bal. This indicates that the Fe content is the remainder when the RTB permanent magnet containing these elements is taken as 100% by mass.

[0096] Next, hydrogen gas was flowed into the raw alloy at room temperature for 1 hour to absorb hydrogen, and then the atmosphere was switched to Ar gas, and dehydrogenation treatment was carried out at 600°C for 1 hour, and the raw alloy was hydrogen-absorbed and crushed.

[0097] Next, 0.1% by mass of oleic acid amide was added as a grinding aid to the raw alloy powder, and the mixture was mixed using a Nauta mixer.

[0098] The mixture was then pulverized in a nitrogen gas stream using a collision plate jet mill to obtain a fine powder (raw powder) with an average particle size of about 3.5 μm, where D50 was measured using a laser diffraction particle size distribution analyzer.

[0099] The obtained fine powder was compacted in a magnetic field to produce a compact. The applied magnetic field was a static magnetic field of 1200 kA / m. The pressure during compaction was 120 MPa. The direction of the applied magnetic field and the pressure direction were perpendicular to each other.

[0100] Next, the compact was sintered to obtain a sintered body. The optimum sintering conditions differ depending on the composition, etc., but were maintained at a temperature between 1050°C and 1100°C for 4 hours. The sintering atmosphere was vacuum. After that, a first aging treatment was performed in an Ar atmosphere at atmospheric pressure at a first aging temperature T1 of 850°C for 1 hour, and then a second aging treatment was performed at a second aging temperature T2 of 520°C to 560°C for 1 hour.

[0101] (Preparation of diffusion material paste) Next, a diffusion material paste to be used for grain boundary diffusion was prepared.

[0102] First, hydrogen gas was flowed through 99.9% pure Tb metal to absorb hydrogen. The atmosphere was then switched to Ar gas, and dehydrogenation treatment was carried out at 600°C for 1 hour, resulting in hydrogen absorption and pulverization of the Tb metal. Next, 0.05% by mass of zinc stearate was added as a grinding aid relative to 100% by mass of Tb metal, and the mixture was mixed using a Nauta mixer. Then, fine pulverization was carried out using a jet mill in an atmosphere containing 3000 ppm of oxygen, yielding a finely pulverized powder of Tb hydride with an average particle size of approximately 10.0 μm.

[0103] Next, finely pulverized powder of neodymium hydride with an average particle size of approximately 10.0 μm was obtained from metallic neodymium with a purity of 99.9%. The method for obtaining the finely pulverized powder of neodymium hydride was the same as that for obtaining the finely pulverized powder of terbium hydride.

[0104] A diffusion material paste was prepared by kneading 46.8 parts by mass of finely pulverized powder of Tb hydride, 17.0 parts by mass of finely pulverized powder of Nd hydride, 11.2 parts by mass of metallic Cu powder, 23 parts by mass of alcohol, and 2 parts by mass of acrylic resin. The alcohol was the solvent, and the acrylic resin was the binder.

[0105] (Application of diffusion paste and heat treatment) The sintered body was processed into a size of 11 mm long x 11 mm wide x 4.2 mm thick (thickness in the direction of easy magnetization: 4.2 mm). Then, an etching treatment was performed by immersing the body in a mixed solution of nitric acid and ethanol (100 parts by mass of ethanol and 3 parts by mass of nitric acid) for 3 minutes, followed by immersion in ethanol for 1 minute. This etching treatment of immersion in the mixed solution for 3 minutes and then immersion in ethanol for 1 minute was performed twice.

[0106] Next, the above-mentioned diffusion material paste was applied to the entire surface of the sintered body after etching. The amount of diffusion material paste applied was adjusted so that the final RTB permanent magnet had the composition shown in Tables 1 and 2.

[0107] Next, the sintered body coated with the diffusion material paste was placed in an oven at 160°C to remove the solvent in the diffusion material paste. It was then heated at 930°C for 18 hours while flowing Ar at atmospheric pressure (1 atm). It was then heated at 520-560°C for 4 hours while flowing Ar at atmospheric pressure. As a result, the RTB-based permanent magnet samples shown in Tables 1 and 2 were obtained.

[0108] The surface of the RTB permanent magnet was scraped off by 0.1 mm on each side, and then the composition, sinterability, and magnetic properties were evaluated.

[0109] The average composition of each of the resulting RTB sintered magnets was measured. Each sample was pulverized using a stamp mill and subjected to analysis. The amounts of various elements were measured using X-ray fluorescence analysis. The B content was measured using ICP analysis. The O content was measured using inert gas fusion / non-dispersive infrared absorption spectroscopy, the C content was measured using oxygen flow combustion / infrared absorption spectroscopy, and the N content was measured using inert gas fusion / thermal conductivity spectroscopy. The compositions of the RTB permanent magnets were confirmed to be those listed in Tables 1 and 2.

[0110] The sinterability was evaluated by measuring the density of each experimental example. 3 If the sintering strength is 7.45Mg / m or more, the sintering strength is considered acceptable. 3For experimental examples in which the sinterability was unsatisfactory, the magnetic properties were not measured.

[0111] The RTB permanent magnets were processed by vertical machining to a size of 11 mm long x 11 mm wide x 4.2 mm thick (the easy axis of magnetization is 4.2 mm), and their magnetic properties were evaluated at room temperature using a BH tracer. Prior to measuring the magnetic properties, the RTB permanent magnets were magnetized in a pulsed magnetic field of 4000 kA / m. Because the RTB permanent magnets are thin, the magnetic properties were evaluated by stacking three magnets. In this example, in addition to the HcJ at room temperature, the HcJ was also measured when heated to 160°C.

[0112] In this example, a Br of 1475 mT or more at room temperature was considered good, and 1490 mT or more was considered even better. An HcJ of 690 kA / m or more at 160°C was considered good, and 700 kA / m or more was considered even better.

[0113] If the Br at room temperature and HcJ at 160°C of an RTB permanent magnet were both good, the magnetic properties of the RTB permanent magnet were rated as acceptable. If either Br at room temperature or HcJ at 160°C were not good, the magnetic properties of the RTB permanent magnet were rated as unacceptable. The results are shown in Tables 1 and 2.

[0114] [Table 1]

[0115] [Table 2]

[0116] Table 1 lists examples and comparative examples carried out under the same conditions except for varying the type and content of R in the RTB permanent magnets. All examples with compositions within a specific range had good magnetic properties. In contrast, sample No. 1, which had too large a TRE, showed a decrease in Br. Sample No. 9, which had too small a TRE, showed poor sinterability.

[0117] Table 2 lists examples and comparative examples in which the B, Al, Ga, and Zr contents of RTB-based permanent magnets were varied. All examples with compositions within the specified ranges had excellent magnetic properties. In contrast, comparative examples with B, Al, Ga, or Zr contents outside the specified ranges exhibited reduced Br and / or HcJ at 160°C.

[0118] For all the RTB-based permanent magnets of the examples and comparative examples, the Tb concentration gradient was analyzed using an electron probe microanalyzer (EPMA), and it was confirmed that the Tb concentration gradient decreased from the outside to the inside. [Explanation of symbols]

[0119] 1...RTB permanent magnet

Claims

1. An R-T-B system permanent magnet in which R is a rare earth element, T is an iron group element, and B is boron, and R contains a light rare earth element and a heavy rare earth element, the R-T-B system permanent magnet further contains Al, Ga, and Zr, The R-T-B system permanent magnet is taken as 100% by mass, the total content of R is 28.50 mass% to 30.25 mass% (not including 28.50 mass%), The B content is 0.93 mass% to 0.98 mass%; The Al content is 0.03 mass% to 0.10 mass%; The Ga content is 0.03 mass % to 0.15 mass %; An RTB-based permanent magnet characterized in that the Zr content is 0.30 mass % to 0.50 mass %.

2. The R-T-B system permanent magnet according to claim 1, wherein the total content of light rare earth elements is 28.50% by mass to 29.50% by mass, and the total content of heavy rare earth elements is 0% by mass to 0.75% by mass (excluding 0% by mass).

3. 3. The RTB system permanent magnet according to claim 1, further comprising Pr in an amount of 0.01 to 1.00 mass %.

4. 3. The RTB system permanent magnet according to claim 1, which is substantially free of Pr.

5. 5. The RTB system permanent magnet according to claim 1, wherein the concentration of the heavy rare earth element is gradually decreased from the surface toward the interior of the magnet.

6. A motor comprising the RTB system permanent magnet according to any one of claims 1 to 5.

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