JP5049722B2 - Sintered body manufacturing method and neodymium iron boron based sintered magnet manufactured by this sintered body manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a sintered body, and more specifically, a process (vacuum evaporation process) of preferentially evaporating rare earth elements from a neodymium iron boron-based (Nd-Fe-B-based) sintered magnet, For producing ultra-high performance magnets by simultaneously carrying out the treatment (vacuum vapor treatment) for diffusing dysprosium (Dy) and terbium (Tb) into the grain boundary phase, which greatly improves the magnetocrystalline anisotropy of the phase. The present invention relates to a method for manufacturing a sintered body.

  Nd-Fe-B based sintered magnets (so-called neodymium magnets) can be manufactured at low cost by being made of a combination of iron and Nd and B elements that are inexpensive and abundant in resources and can be stably supplied. In addition, since it has high magnetic properties (the maximum energy product is about 10 times that of ferrite magnets), it is used in various products such as electronic equipment, and is also used in motors and generators for hybrid cars. is increasing.

Nd-Fe-B magnets are mainly produced by powder metallurgy. In this method, Nd, Fe, and B are first blended at a predetermined composition ratio, and melted and cast to produce an alloy raw material. For example, it is roughly pulverized by, for example, a hydrogen pulverization process, and then finely pulverized by, for example, a jet mill pulverization process to obtain alloy raw material powder. Next, the obtained alloy raw material powder is oriented in a magnetic field (magnetic field orientation), and compression molded in a state where a magnetic field is applied to obtain a compact. And this sintered compact is sintered on predetermined conditions, and a sintered magnet is produced (refer patent document 1).
JP 2004-6761 A

By the way, the R ₂ T ₁₄ B phase (main phase component) responsible for the magnetism of the Nd—Fe—B based sintered magnet is not directly generated from the liquid phase in an equilibrium state, and firstly γ iron is generated as an initial phase. It is formed by the reaction between the liquid phase and its iron (peritectic reaction) (γ iron transforms into α iron with decreasing temperature). In this case, for example, even if the alloy raw material is melted and cast by the strip casting method (SC method), which is a rapid cooling method with a rapid solidification cooling rate, if the Nd content is 28.5% or less, the production of α iron It is known that it is difficult to suppress, and it is formed in a dendrite form in the alloy.

  If alpha iron is formed in a dendritic form in the alloy and is three-dimensionally connected, the pulverizability of the alloy in the subsequent pulverization step is significantly impaired. In other words, if the grindability is poor, the particles are once coarsely pulverized by the hydrogen pulverization process, and then the particle shapes suitable for producing sintered magnets with high magnetic properties are prepared even if the pulverization is attempted by the jet mill pulverization process. It is difficult to obtain fine powder particles. In addition, coarse grains (due to α-iron produced in a dendritic form) remain in the jet mill, and composition deviation tends to occur due to an increase in the amount of fine powder collected by the bag filter, making quality control difficult. There is a problem that there is.

On the other hand, if the Nd content is more than 28.5%, it is possible to produce an ingot that does not produce α iron, but the R-rich phase increases and the volume ratio of the R ₂ T ₁₄ B phase that plays a role in magnetism. Therefore, there arises a problem that it becomes difficult to manufacture a high-performance magnet having a maximum energy product ((BH) max) and a large residual magnetic flux density (Br) exhibiting magnetic characteristics.

  In addition, in this type of magnet, if the coercive force (kOe) is further increased, a magnet having a strong magnetic force can be obtained even if the thickness of the magnet itself is reduced. And lower power consumption. For this reason, development of an ultra-high performance magnet having a higher coercive force than that of the prior art is also desired.

  In view of the above, an object of the present invention is to provide a method for manufacturing a sintered body that can improve product functions such as improvement of magnetic properties of a permanent magnet.

In order to solve the above-mentioned problems, the method for producing a sintered body according to the present invention obtains a primary sintered body by liquid phase sintering, and then stores the primary sintered body in a processing chamber and is lower than the sintering temperature. By heating in a vacuum atmosphere at a temperature, the element having a high vapor pressure in the liquid phase component is preferentially evaporated to reduce or eliminate the volume ratio of the liquid phase, while the same as the primary sintered body or Predetermined metal evaporating materials housed in different processing chambers are heated and evaporated in a vacuum atmosphere, and the evaporated metal atoms are attached to the surface of the primary sintered body, and the attached metal atoms are crystallized in the primary sintered body. A method of manufacturing a sintered body that diffuses into a grain boundary phase , wherein the raw material alloy is for a neodymium iron boron based sintered magnet having a predetermined rare earth element, and the content of the rare earth element is 28.5. It is characterized by being from 30% by weight to 30% by weight .

According to the present invention, among the liquid phase components contributing to the promotion of sintering, elements having a high vapor pressure are preferentially evaporated to reduce the volume ratio of the liquid phase, etc., thereby exhibiting the original characteristics of the main phase. be able to. In particular, when the primary sintered body is an R ₂ T ₁₄ B phase magnet, the rare earth elements are efficiently evaporated, the volume ratio of the R rich phase is reduced, and the R ₂ T ₁₄ B phase (main phase component) that plays a role in magnetism ) Can be increased to improve the maximum energy product ((BH) max) and the residual magnetic flux density (Br) exhibiting magnetic characteristics.

Simultaneously with the treatment as described above, the original characteristics of the main phase can be further improved by diffusing predetermined metal atoms that improve the characteristics of the main phase into the grain boundary phase. In particular, by increasing the volume ratio of the R ₂ T ₁₄ B phase responsible for magnetism, the maximum energy product ((BH) max) and residual magnetic flux density (Br) exhibiting magnetic characteristics are improved, while the main phase By diffusing Dy and Tb, which greatly improve the magnetocrystalline anisotropy, into the grain boundary phase, the mechanism of generating a new coercive force is strengthened. As a result, the maximum energy product is hardly impaired. The coercive force is greatly improved, and as a result, an ultra-high performance magnet is obtained.

  As described above, in the present invention, the element having a high vapor pressure among the liquid phase components is preferentially evaporated to reduce the volume ratio of the liquid phase, and a predetermined metal atom that improves the characteristics of the main phase is added to the process. Since the treatment for diffusing into the crystal grain boundary phase is performed at the same time, the treatment time can be greatly reduced as compared with the case where both treatments are carried out sequentially, and high productivity can be achieved.

  In this case, it is preferable that the evaporated metal atoms are diffused into the grain boundary phase of the secondary sintered body before the thin film made of the metal evaporation material is formed on the surface of the secondary sintered body. According to this, the magnet surface is prevented from being deteriorated, and a magnet with excellent productivity that does not require finishing is obtained.

  In the present invention, the primary sintered body is preferably obtained by manufacturing a raw material alloy by a strip casting method or a centrifugal casting method, and then performing pulverization, magnetic field forming, and sintering processes.

According to this, the main phase component is composed of an R ₂ T ₁₄ B phase, R is at least one rare earth element mainly containing Nd, T is a transition metal mainly containing Fe, and R ₂ T _{14 When the} excess R from the B-phase stoichiometric composition is a R-rich phase, particularly a sintered magnet that becomes a liquid phase during sintering and helps promote sintering, for example, when melting and casting a raw material alloy In order to prevent the formation of dendritic α-iron in the alloy, the content of rare earth elements is set to be large, an ingot that does not generate α-iron is produced, and a sintered magnet is obtained by a known process. By evaporating only the rare earth element, the volume ratio of the Nd-rich phase is reduced, and as a result, the maximum energy product ((BH) max) and residual magnetic flux density (Br) exhibiting magnetic characteristics can be improved.

  Simultaneously with the above treatment, the metal evaporation material is treated as dysprosium, terbium, or an alloy containing one of these by evaporating Dy and Tb and diffusing Dy atoms into the grain boundary phase of the sintered magnet. The magnetic force can be improved, and as a result, an ultra-high performance magnet can be obtained.

The pressure in the vacuum atmosphere is preferably set to 10 ⁻⁴ Pa or less. When the pressure is higher than 10 ⁻⁴ Pa, the elements having a high vapor pressure in the liquid phase component are preferentially evaporated, and the metal atoms of Dy and Tb cannot be efficiently diffused into the crystal grain boundary phase of the sintered magnet.

  Further, in order to supply evaporated metal atoms so that a thin film made of a metal evaporation material is not formed on the surface of the primary sintered body, the evaporated metal atoms are disposed in the processing chamber, and a plurality of fine particles are arranged. It is preferable to adopt a configuration in which the sintered magnet is supplied through each opening of the adjusting plate in which the opening is formed.

  In addition, the sintered compact manufactured by the method of any one of Claims 1 thru | or 7 is a neodymium iron boron series sintered magnet, for example.

Referring to FIG. 1, 1 is a process for preferentially evaporating rare earth elements from a sintered magnet S in a vacuum atmosphere to a neodymium iron boron-based sintered magnet (primary sintered body) S ( Ultra-high performance by simultaneously performing vacuum evaporation) and diffusion of dysprosium (Dy) and terbium (Tb) (vacuum vapor), which greatly improves the magnetocrystalline anisotropy of the main phase, into the grain boundary phase. A vacuum processing apparatus for obtaining a magnet. The vacuum evaporation apparatus 1 includes a vacuum chamber 3 that can be held at a reduced pressure to a predetermined pressure (for example, 10 ⁻⁵ Pa) through a vacuum exhaust unit 2 such as a turbo molecular pump, a cryopump, or a diffusion pump. A cylindrical sintered body case 4 having an open upper surface can be freely installed and removed in the vacuum chamber 3, and a space surrounded by the sintered body case 4 constitutes a processing chamber 4 a. In the processing chamber 4a, a plurality of mounting portions 4b formed by arranging a plurality of wire rods (for example, φ0.1 to 10 mm) in a lattice shape are formed at predetermined intervals in the height direction from the bottom surface, A plurality of sintered magnets S can be placed side by side on the placement portion 4b.

  In addition, the metal case V can be appropriately disposed on the bottom surface, the side surface or the top surface of the sintered body case 4 so as to be separated from the sintered magnet S. As the metal evaporation material V, dysprosium (Dy), terbium (Tb) or an alloy containing at least one of them is used to greatly improve the magnetocrystalline anisotropy of the main phase, and the coercive force is further increased in the alloy. Therefore, Nd, Al, Cu, Ga and the like are included. The metal evaporation material V is blended at a predetermined mixing ratio, for example, an arc melting furnace is used to obtain a bulk (substantially spherical) alloy, and the ratio of 1 to 10% by weight of the sintered magnet S per unit volume. The surface area (specific surface area) is reduced and disposed in the processing chamber 4a.

  As will be described later, the sintered body case 4 and the mounting portion 4b heat the sintered magnet S and the metal evaporating material V, so that the rare earth-rich phase Nd, Pr, etc., which is a liquid phase from the sintered magnet S. The rare earth element R is preferentially evaporated, and when the metal evaporation material V of Dy or Tb is evaporated, the rare earth element R is made of a material that does not react with the rare earth element R. That is, when the evaporated rare earth element R adheres to the surface of the sintered body case 4 or the mounting portion 4b and forms a reaction product on the surface, recovery of the evaporated rare earth element R including Dy and Tb is performed. May be difficult. For this reason, the sintered body case 4 and the mounting portion 4b are manufactured from Mo or SUS, in which the rare earth element R adhering to the surface is easily peeled, or Mo or the like is used as a lining film on the surface of another heat insulating material. It consists of a film. In this case, since the rare earth element R also adheres to the wall surface of the vacuum chamber 3, a shield plate (not shown) in which a lining film made of the above material is formed on the surface is provided in order to facilitate recovery. It is preferable.

  The vacuum chamber 3 is provided with heating means 5 so as to surround the periphery of the sintered body case 4. The heating means 5 is an electric heater (not shown) composed of a plurality of annular filaments arranged over the entire length so as to surround the periphery of the sintered body case 4, and each filament is a vacuum chamber. 3 is supported by a support piece (not shown) provided in the interior. In this case, the filament is also composed of Mo or the like that does not react with the rare earth element R. Then, by heating the sintered body case 4 by the heating means 5 under reduced pressure, the sintered magnet S placed on the processing chamber 4a, and thus on the placing portion 4b, indirectly through the sintered body case 4. In addition, the metal evaporation material V can be heated substantially uniformly.

  A trap plate 6 is disposed above the sintered body case 4 so as to cover the upper surface of the opening. The trap plate 6 is a rare earth element R evaporated from the sintered magnet S and Dy evaporated from the metal evaporation material V. Of the atoms and Tb atoms, they play the role of attaching and collecting those discharged through the opening on the upper surface of the sintered body case 4 without attaching to the surface of the sintered magnet D. The trap plate 6 is also made of a material that does not react with the evaporated rare earth element R including Dy and Tb and that adheres to the surface easily peels off, for example, Mo. In this case, the volume of the processing chamber 4a is determined in consideration of the mean free path of the rare earth element R, and in particular, the rare earth element R evaporated from the sintered magnet S repeatedly or directly collides with the inner wall of the sintered body case 4. It is set to be discharged to the outside through the upper surface opening, and the distance from the upper end of the sintered body case 4 to the trap plate 6 is set so that most of the discharged rare earth element R adheres. Yes. In this case, the sintered body case 4 may be provided with, for example, a cooling means by circulating a refrigerant so that the rare earth element R evaporated by the temperature difference adheres to and accumulates on the trap plate 6.

  Next, production of an ultra-high performance magnet (permanent magnet) will be described. The raw material alloy powder is produced as follows. That is, industrial pure iron, metallic neodymium, and low carbon ferroboron are blended and dissolved using a vacuum induction furnace so that Fe, Nd, and B have a predetermined composition ratio, and then quenched by a rapid cooling method such as a strip casting method. First, a raw material alloy of 05 mm to 0.5 mm is prepared. Alternatively, a raw material alloy having a thickness of about 5 to 10 mm may be produced by a centrifugal casting method, and Dy, Tb, Co, Cu, Nb, Zr, Al, Ga, or the like may be added during blending. . In this case, the total content of rare earth elements is set to more than 28.5%, and an ingot that does not produce α iron is obtained.

  Next, the produced raw material alloy is coarsely pulverized by a known hydrogen pulverization step, and then finely pulverized in a nitrogen gas atmosphere by a jet mill pulverization step to obtain a raw material alloy powder having an average particle diameter of 3 to 10 μm. Next, the raw material alloy powder is compression molded into a predetermined shape in a magnetic field using a known compression molding machine. Next, the molded body taken out from the compression molding machine is housed in a sintering furnace (not shown), sintered in a vacuum at a predetermined temperature (for example, 1050 ° C.) for a predetermined time (sintering process), and further, a predetermined temperature (500 And a sintered magnet (primary sintered body) S is obtained.

Next, using the vacuum processing apparatus 1 shown in FIG. 1, the sintered magnet S is simultaneously subjected to a vacuum evaporation process and a vacuum vapor process using Tb as the metal evaporation material V. That is, the sintered magnet S produced as described above is placed on the placement portion 4b of the sintered body case 4, and bulk Tb as the metal evaporation material V is formed on the bottom surface of the sintered body case 4. Is installed. And after installing the sintered compact case 4 which accommodated the sintered magnet S and the metal evaporation material V in the position enclosed by the heating means 5 in the vacuum chamber 3, the vacuum exhaust means 2 is operated and predetermined pressure ( For example, the vacuum chamber 3 is depressurized until it reaches 10 ⁻⁵ Pa). After the inside of the vacuum chamber 3 reaches a predetermined pressure, the heating means 5 is operated to heat the processing chamber 4a, and consequently the sintered magnet S and the metal evaporation material, by V, and after reaching the predetermined temperature, this state is maintained for a predetermined time. To do.

In this case, the heating temperature is set to 900 ° C. or higher and lower than the sintering temperature (for example, 1100 ° C.). If the temperature is lower than 900 ° C., the rare earth element R and the metal evaporation material V, Tb, cannot be efficiently evaporated. If the sintering temperature is exceeded, abnormal grain growth occurs, the magnetic properties are greatly reduced, and the vapor of Tb The pressure increases and Tb atoms in the vapor atmosphere are excessively supplied to the surface of the sintered magnet S. In addition, an open / close valve 8 whose opening degree can be adjusted is provided in an exhaust passage (exhaust pipe) 7 that connects the vacuum chamber 3 and the vacuum exhaust means 2, and the opening degree of the open / close valve 8 is adjusted so that the vacuum chamber 3, As a result, the pressure in the processing chamber 4a is set to a pressure of 10 ⁻⁴ Pa or less. When the pressure is higher than 10 ⁻⁴ Pa, the rare earth element R and the metal evaporation material V, Tb, cannot be efficiently evaporated.

Thereby, due to the difference in vapor pressure at a constant temperature (for example, at 1000 ° C., the vapor pressure of Nd is 10 ⁻³ Pa, the vapor pressure of Fe is 10 ⁻⁵ Pa, and the vapor pressure of B is 10 ⁻¹³ Pa). Only the rare earth element R in the R-rich phase evaporates. For this reason, the ratio of the Nd-rich phase is reduced, and the maximum energy product ((BH) max) and the residual magnetic flux density (Br) exhibiting magnetic characteristics are improved. In addition, the Tb atoms evaporated in the above temperature range are supplied or adhered to the surface of the sintered magnet S heated to a predetermined temperature from a plurality of directions by repeatedly colliding directly or on the side wall of the sintered body case 4. Then, the adhered Tb atoms are diffused into the grain boundary phase of the sintered magnet S, and a Tb rich phase (phase containing Dy in the range of 5 to 80%) is formed in the grain boundary phase. For this reason, the coercive force generation mechanism of the new creation type is strengthened, and the coercive force is dramatically improved without substantially damaging the maximum energy product. The result is an ultra-high performance magnet.

  Here, the processing time is such that the rare earth element R content of the permanent magnet is less than 28.5 wt%, or the average concentration reduction of the rare earth element R is 0.5 wt% or more. It is appropriately set so that a Tb rich phase is formed in the boundary phase.

  Further, by evaporating Tb in the above pressure and heating temperature range, the vapor pressure of Tb is lowered, the evaporation amount is reduced, and the supply amount of Tb atoms to the sintered magnet S is suppressed, Combined with the fact that the sintered magnet is heated to a range where an optimum diffusion rate can be obtained, Tb atoms attached to the surface of the sintered magnet S are deposited on the surface of the sintered magnet S to form a Tb layer (thin film). ) Is efficiently diffused into the grain boundary phase before it is formed (see FIG. 2). As a result, the surface of the magnet M is prevented from being deteriorated, and an ultra-high performance magnet (permanent magnet) M excellent in productivity that does not require finishing is obtained. In this case, the processing time can be significantly reduced as compared with the case where the vacuum evaporation process and the vacuum vapor process are sequentially performed, and higher productivity can be achieved.

  Next, after the above processing is performed, the operation of the heating means 5 is temporarily stopped, and the open / close valve 8 is fully opened to cool the vacuum chamber 3 while evacuating it, and the temperature in the processing chamber 4a is once lowered to, for example, 500 ° C. . Subsequently, the heating means 5 is actuated again, the temperature in the processing chamber 4a is set in the range of 550 ° C. to 650 ° C., and heat treatment for further improving the magnetic properties is performed. Finally, it is cooled to approximately room temperature and the permanent magnet M is taken out.

In the present embodiment, the example in which Tb is used as the metal evaporation material installed in the sintered body case 4 has been described as an example. However, the present invention is not limited to this, and Dy can be used. In this case, when the temperature in the processing chamber 4a is 900 ° C. to 1000 ° C., the saturated vapor pressure of Dy is about 1 × 10 ⁻² to 1 × 10 ⁻¹ Pa, and thus the processing chamber 4a exceeded 900 ° C. When heated at a temperature, the vapor pressure of Dy increases and Dy atoms in the vapor atmosphere are excessively supplied to the surface of the sintered magnet S. At this time, Dy diffuses into the crystal grains and greatly reduces the magnetization in the crystal grains, so that the maximum energy product and the residual magnetic flux density are reduced.

  Therefore, as shown in FIGS. 3A and 3B, when the metal evaporation material V is mainly Dy, the box 11 having an upper surface opened on the bottom surface of the sintered body case 4 and A Mo evaporation box 13 composed of a lid 12 that closes the upper surface opening of the box is installed, and Dy evaporated to a sintered magnet through a fine through hole 14 (φ0.1 to 5 mm) formed in the lid 12. It is preferable to supply atoms. In this case, the lid body 12 constitutes an adjustment plate.

  On the other hand, although not particularly illustrated, an evaporation chamber (another processing chamber) which is another vacuum chamber is connected to the vacuum chamber 3 via a communication path, and only the metal evaporation material V is installed in the other vacuum chamber, The metal evaporation material V can be heated and evaporated separately from the vacuum chamber 3, and the evaporated Dy atoms are supplied to the sintered magnet through the opening provided in the bottom surface of the sintered body case 4. It may be. In this case, an adjustment plate in which a plurality of fine through holes are formed in the communication path may be provided.

  Furthermore, in the present embodiment, the manufacture of the sintered magnet S has been described as an example. However, the function of the sintered body is determined by evaporating a specific substance from the sintered body and diffusing a specific metal element into the crystal grain boundary phase. If it can improve, the manufacturing method of the sintered compact of this invention can be applied.

  In Example 1, a permanent magnet was obtained using the vacuum processing apparatus 1 shown in FIG. First, industrial pure iron, metallic neodymium, low carbon ferroboron, electrolytic cobalt, and pure copper are used as raw materials so that the composition is 29Nd-1B-0.1Cu-1Co-BalFe (wt%), and vacuum induction melting is performed. And a flaky ingot having a thickness of about 0.3 mm was obtained by a strip casting method. Next, it was coarsely pulverized once by a hydrogen pulverization step, and then finely pulverized by, for example, a jet mill pulverization step to obtain a raw material alloy powder.

  Next, a compact was obtained using a transverse magnetic field compression molding apparatus having a known structure, and then sintered in a vacuum sintering furnace at a temperature of 1050 ° C. for 2 hours to obtain a sintered magnet S. Then, the primary sintered body was processed into a shape of 40 × 10 × 3 mm by wire cutting, and then finished to have a surface roughness of 10 μm or less, and then the surface was etched with dilute nitric acid.

  Subsequently, the said process was performed using the vacuum evaporation apparatus 1 shown in FIG. The 100 sintered magnets S are arranged at equal intervals on the mounting portion 4b in the processing chamber 4a, and the bottom surface of the sintered body case 4 has a purity of 99.9% and a massive Tb as a metal evaporation material V. (About φ1 mm) was placed in a total amount of 3 kg.

Next, after the sintered body case 4 in which the sintered magnet S and the metal evaporating material V are set is housed in a predetermined position of the vacuum chamber 3, the vacuum exhaust means 2 is operated to bring the vacuum chamber to 1 × 10 ⁻⁵ Pa. The pressure was reduced and the heating means 5 was operated to heat. The heating temperature of the processing chamber 4a was set to 1000 ° C., and after the temperature of the processing chamber 4a reached 1000 ° C., the above processing was performed for 10 hours.

FIG. 4 shows the magnetic characteristics (BH curve tracer) of the permanent magnet M when the above processing is performed by adjusting the opening of the opening / closing valve 8 to change the pressure in the processing chamber 4a from 1 Pa to 2 × 10 ⁻⁵ Pa. It is a table | surface which shows the average value of measurement. According to this, at a pressure of 10 ⁻³ Pa, the maximum energy product indicating magnetic characteristics is 53.6 MG0e, the residual magnetic flux density is 14.62 kG, and the coercive force is 12.6 kOe. It can be seen that an ultra-high performance permanent magnet cannot be obtained.

On the other hand, at a pressure of 10 ⁻⁴ Pa or less, the maximum energy product indicating magnetic characteristics is 56 MG0e, the residual magnetic flux density is 14.87 kG, and the coercive force is 27.5 kOe, and the pressure is 10 ⁻³ Pa. It can be seen that an ultra-high performance permanent magnet having a coercive force more than double that of a higher pressure can be obtained.

In Example 2, a sintered magnet S was produced under the same conditions as in Example 1. Next, the vacuum evaporator 1 is used, the heating temperature is fixed at 900 ° C., the evaporation time is fixed at 10 hours, the opening of the on-off valve 8 is adjusted, and the pressure in the processing chamber 4a is changed from 2 Pa to 2 × 10 ⁻⁵ Pa. The above vacuum treatment was performed.

  Also, as the metal evaporating material V, a massive Dy (about φ1 mm) with a purity of 99.9% is used, placed in the evaporation box 13 (see FIG. 3) in a total amount of 3 kg, and then installed on the bottom surface of the sintered body case 4 did. A through hole having a diameter of 0.2 to 0.5 mm was formed in the lid of the evaporation box 13 so that the opening ratio with respect to the area of the top surface of the lid was 1%.

FIG. 5 is a table showing the average value of the magnetic properties (measured by a BH curve tracer) of the permanent magnet M when the above processing is performed. According to this, at a pressure of 10 ⁻³ Pa, the maximum energy product indicating magnetic characteristics is 53.1MG0e, the residual magnetic flux density is 14.61 kG, and the coercive force is 13.5 kOe. It can be seen that an ultra-high performance permanent magnet cannot be obtained.

On the other hand, at a pressure of 10 ⁻⁴ Pa or less, the maximum energy product indicating magnetic properties is 55.6 MG0e, the residual magnetic flux density is 14.86 kG, the coercive force is 22.5 kOe, and the pressure is 10 ⁻³ Pa. It can be seen that ultra-high performance permanent magnets can be obtained compared to higher pressures.

The figure explaining roughly the vacuum processing apparatus which enforces the manufacturing method of this invention. The figure which illustrates typically the cross section of the magnet when a vacuum process is performed. The figure explaining roughly the modification of the vacuum processing apparatus which enforces the manufacturing method of this invention. 2 is a table showing magnetic characteristics of sintered magnets produced in Example 1. 6 is a table showing magnetic characteristics of sintered magnets produced in Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum evaporation apparatus 3 Vacuum chamber 4 Sintered body case 4a Processing chamber 5 Heating means 6 Trap board S Primary sintered body (sintered magnet)
R Rare earth element V Metal evaporation material (Dy, Tb)

Claims (7)

After obtaining a primary sintered body by liquid phase sintering, the primary sintered body is stored in a processing chamber and heated in a vacuum atmosphere at a temperature lower than the sintering temperature. Preferentially evaporates high-elements and reduces or eliminates the volume ratio of the liquid phase while heating a predetermined metal evaporation material stored in the same or different processing chamber as the primary sintered body in a vacuum atmosphere. Evaporating, attaching the evaporated metal atoms to the surface of the primary sintered body, and diffusing the attached metal atoms into the grain boundary phase of the primary sintered body ,
The raw material alloy is for a neodymium iron boron sintered magnet having a predetermined rare earth element, and the rare earth element content is 28.5 wt% or more and 30 wt% or less. Body manufacturing method.   The sintered body according to claim 1, wherein the evaporated metal atoms are diffused into a grain boundary phase of the primary sintered body before a thin film made of a metal evaporation material is formed on the surface of the primary sintered body. Manufacturing method.   The primary sintered body is obtained by manufacturing a raw material alloy by a strip casting method or a centrifugal casting method, and thereafter performing pulverization, magnetic field forming, and sintering processes. Item 3. A method for producing a sintered body according to Item 2. The method for producing a sintered body according to any one of claims 1 to 3, wherein the metal evaporation material is dysprosium, terbium, or an alloy containing any one of them . The pressure of the said vacuum atmosphere is set to 10 <^-4> Pa or less, The manufacturing method of the sintered compact of any one of Claims 1-4 characterized by the above-mentioned . The evaporated metal atoms, according to claim 5, characterized in that it has to be supplied to the sintered magnet through the openings of the adjusting plate disposed in the processing chamber and a plurality of fine openings are formed The manufacturing method of the sintered compact of this. A neodymium iron boron-based sintered magnet manufactured by the method according to any one of claims 1 to 6 .