JP5117220B2 - Method for manufacturing permanent magnet - Google Patents

Description

  The present invention relates to a method for manufacturing a permanent magnet, and more particularly, to a permanent magnet having a high magnetic property obtained by diffusing Dy or Tb into a crystal grain boundary and / or a crystal grain boundary phase of an Nd—Fe—B based sintered magnet. It relates to a method of manufacturing.

  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.

  Since the Curie temperature of the sintered magnet is as low as about 300 ° C., the temperature may rise above a predetermined temperature depending on the usage status of the product to be used. There is. In addition, when the sintered magnet is used for a desired product, the sintered magnet may be processed into a predetermined shape, and this processing may cause defects (cracks, etc.) or distortions in the crystal grains of the sintered magnet. There is a problem that the magnetic properties are significantly deteriorated.

  For this reason, conventionally, a rare earth metal selected from Yb, Eu, and Sm is placed in a processing chamber in a state of being mixed with an Nd—Fe—B based sintered magnet, and the processing chamber is heated to thereby form a rare earth metal. By evaporating the metal, sorbing the evaporated rare earth metal atoms to the sintered magnet, and further diffusing the metal atoms into the grain boundary phase of the sintered magnet, It is known that a metal is introduced to improve or recover the magnetization and coercive force (Patent Document 1).

  Here, among the rare earth metals, Dy and Tb have a magnetic anisotropy of 4f electrons larger than Nd, and have a negative Stevens factor similar to Nd, thereby greatly improving the magnetocrystalline anisotropy of the main phase. It is known to let However, if Dy or Tb is added at the time of producing the sintered magnet, Dy and Tb have a ferrimagnetic structure in which the spin arrangement is opposite to Nd in the main phase crystal lattice, so that the magnetic field strength, and hence the magnetic The maximum energy product showing the characteristics is greatly reduced.

  Therefore, it is proposed to use Dy and Tb and to introduce a desired amount of Dy and Tb uniformly and into the grain boundaries and / or grain boundary phases by the above method. As Dy and Tb exist (that is, a thin film of Dy and Tb is formed on the surface of the sintered magnet), when vaporized metal atoms of Dy and Tb are supplied, they are deposited on the surface of the sintered magnet. There arises a problem that the metal atoms are recrystallized and the surface of the sintered magnet is remarkably deteriorated (surface roughness is deteriorated). In the above-described method in which the rare earth metal and the sintered magnet are mixed, the melted rare earth metal directly adheres to the sintered magnet when the metal evaporation material is heated, thereby avoiding the formation of thin films and protrusions. Absent.

  In addition, if excessive metal atoms are supplied to the sintered magnet surface so that a thin film of Dy and Tb is formed on the sintered magnet surface, it accumulates on the surface of the sintered magnet heated during processing, As the amount of Tb increases, the melting point near the surface decreases, and Dy and Tb deposited on the surface melt and enter excessively into crystal grains particularly close to the surface of the sintered magnet. When entering excessively into the crystal grains, as described above, Dy and Tb take a ferrimagnetic structure in the main phase crystal lattice that has a spin arrangement opposite to Nd, thereby effectively improving magnetization and coercivity. Or there is a possibility that it cannot be recovered.

  That is, once a thin film of Dy or Tb is once formed on the surface of the sintered magnet, the average composition of the sintered magnet surface adjacent to the thin film becomes a rare earth rich composition of Dy or Tb. And the surface of the sintered magnet is melted (that is, the main phase is melted and the amount of the liquid phase is increased). As a result, the vicinity of the surface of the sintered magnet melts and collapses, and the unevenness increases. In addition, Dy excessively penetrates into the crystal grains together with a large amount of liquid phase, and the maximum energy product and the residual magnetic flux density showing the magnetic characteristics are further lowered.

As a solution to such a problem, an iron-boron-rare earth sintered magnet and a metal evaporation material containing at least one of Dy and Tb are stored in a processing box so as to be separated from each other. Heating in a vacuum atmosphere evaporates the metal evaporation material, adjusts the supply amount of the evaporated metal atoms to the surface of the sintered magnet, attaches the metal atoms, and attaches the attached metal atoms to the surface of the sintered magnet It has been proposed by the present applicant to perform a treatment (vacuum vapor treatment) for diffusing into the crystal grain boundaries and / or the grain boundary phases of the sintered magnet before the thin film made of the metal evaporation material is formed on ( International application PCT / JP2007 / 066272).
Japanese Patent Application Laid-Open No. 2004-296773 (for example, refer to the description of claims)

  According to the above vacuum vapor treatment, the surface state of the permanent magnet after the treatment is substantially the same as the state before the treatment and does not require a separate post-process. In addition, Dy and Tb are added to the sintered magnet. Diffusion to crystal grain boundaries and / or grain boundary phases to spread uniformly, so that the grain boundary phase has a rich phase of Dy and Tb (phase containing Dy and Tb in the range of 5 to 80%). Furthermore, Dy and Tb diffuse only in the vicinity of the surface of the crystal grains, and as a result, a high-performance magnet having effectively improved or recovered magnetization and coercive force can be obtained.

  However, in order to obtain such a high-performance magnet, it takes several hours of vacuum steam processing time. To increase mass productivity, the above-mentioned effects of vacuum steam processing and the sintered magnets are stored in a processing box. It is required that a large number of sintered magnets can be accommodated in one processing box (increasing the stacking amount of sintered magnets in the processing box) without impairing the workability.

  Therefore, in view of the above points, the present invention provides a method for producing a mass-produced permanent magnet that can accommodate a large number of sintered magnets in one processing box with good workability, and obtain a high-performance magnet. The task is to do.

In order to solve the above-described problems, a method for manufacturing a permanent magnet according to the present invention includes storing a metal evaporation material containing at least one of Dy and Tb and a ring magnet in a processing box, and placing the processing box in a vacuum chamber. After the installation, the processing box is heated to a predetermined temperature in a vacuum atmosphere to evaporate the metal evaporation material and attach it to the sintered magnet. The attached Dy and Tb metal atoms are separated from the crystal grain boundaries of the sintered magnet. And / or a method for producing a permanent magnet that diffuses into a grain boundary phase, comprising a base on which wires are assembled in a lattice shape and a support that is erected at the points where the vertical and horizontal wires cross each other. Each ring magnet is inserted into each support from above, and a spacer that allows the passage of metal atoms is arranged so that the ring magnets do not come into contact with each other. It is characterized by being configured to . In this case, it is preferable that the jig in which the ring magnet is installed is stacked and stored in the processing box with a plate-shaped metal evaporation material.

According to the present invention, after the metal evaporating material is installed on the bottom surface of the processing box, each of the ring magnets is inserted into each support body from above, and further, there is a predetermined interval above the metal evaporating material. Is installed. And the metal evaporation material and the jig | tool with which the ring magnet was installed are alternately piled up hierarchically to the upper end part of a process box. This makes it possible to increase the number of ring magnets that can be stored in one processing box (the load capacity can be increased) . In this case, by diffusing Dy or Tb atoms to the grain boundaries and / or grain boundary phase of the sintered magnet, it will not be impaired the effect of the vacuum vapor process of magnetizing and improve or recover the coercive force.

  In the present invention, if the metal evaporation material formed in a plate shape is used, the operation of storing the metal evaporation material and the sintered magnet in the processing box together with storing the spacer in the processing box. Can be further improved.

  In addition, the processing box is configured to include a box part having an upper surface opened and a lid part detachably attached to the opened upper surface, the vacuum chamber being evacuated. It is preferable that the inside of the processing box is depressurized as the means is operated to depressurize the vacuum chamber. This eliminates the need for a separate evacuation unit for the processing box, and simplifies the apparatus configuration. Further, the sintered magnet and the metal evaporation material may be accommodated outside the vacuum chamber.

  By the way, as described above, when the metal evaporation material and the sintered magnet are stacked up and down in a sandwich structure in the processing box, the interval between the metal evaporation material and the sintered magnet becomes narrow. When the metal evaporation material is evaporated in such a state, it is strongly influenced by the straightness of the evaporated metal atoms. That is, among the sintered magnets, metal atoms easily adhere to the surface facing the metal evaporation material.For example, when the spacer is configured by assembling thin wires in a lattice shape, It becomes difficult to supply Dy and Tb to the part. For this reason, the permanent magnet subjected to the vacuum vapor treatment has a portion having a high coercive force and a portion having a low coercive force locally, and as a result, the squareness of the demagnetization curve is impaired. In such a case, an inert gas may be introduced into the vacuum chamber while the metal evaporation material is evaporating.

  Thereby, since the mean free path of the metal atoms of Dy and Tb is short, the metal atoms evaporated in the processing box by the inert gas diffuse, and the amount of metal atoms directly attached to the surface of the sintered magnet is reduced. Even if the distance between the sintered magnet and the metal evaporation material is narrow, the evaporated Dy and Tb wrap around to the shadowed portion of the wire. Adhere with. As a result, metal atoms such as Dy and Tb can be prevented from excessively diffusing into the crystal grains, reducing the maximum energy product and residual magnetic flux density, and the presence of locally high and low coercivity portions. It is possible to prevent the squareness of the demagnetization curve from being damaged.

  Referring to FIG. 1, in the present embodiment, the permanent magnet M evaporates the metal evaporation material v on the surface of the Nd—Fe—B sintered magnet S produced in a predetermined shape, A series of treatments (vacuum vapor treatment) are performed simultaneously by attaching the evaporated metal atoms and diffusing them to the crystal grain boundaries and / or crystal grain boundary phases of the sintered magnet S so as to spread uniformly.

  The Nd—Fe—B based sintered magnet S as a starting material is manufactured 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, an alloy raw material of 05 mm to 0.5 mm is prepared. Alternatively, an alloy raw material 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. . The total content of rare earth elements is increased to more than 28.5%, and an ingot that does not produce α iron is obtained.

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

Next, the produced primary sintered body is housed in a vacuum heat treatment furnace (not shown) and heated to a predetermined temperature in a vacuum atmosphere. The heating temperature is set to 900 ° C. or higher and lower than the sintering temperature. When the temperature is lower than 900 ° C., the evaporation rate of the rare earth element is slow, and when the sintering temperature is exceeded, abnormal grain growth occurs and the magnetic properties are greatly deteriorated. Moreover, the pressure in a furnace is set to the pressure of 10 < ^-3 > Pa or less. At pressures higher than 10 ⁻³ Pa, the rare earth elements cannot be evaporated efficiently.

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 elements in the rare earth-rich phase of the primary sintered body evaporate. As a result, the ratio of the Nd-rich phase is reduced, and the sintered magnet S is produced in which the maximum energy product ((BH) max) and the residual magnetic flux density (Br) exhibiting magnetic characteristics are improved. In this case, in order to obtain a high-performance permanent magnet M, the rare earth element content of the permanent magnet M is less than 28.5 wt%, or the average concentration of the rare earth element is reduced to 0.5 wt% or more. Heat treatment. The sintered magnet S thus obtained is subjected to vacuum vapor treatment. A vacuum steam processing apparatus that performs this vacuum steam processing will be described below with reference to FIG.

The vacuum vapor processing apparatus 1 has a vacuum chamber 3 that can be held at a reduced pressure to a predetermined pressure (for example, 1 × 10 ⁻⁵ Pa) via a vacuum exhaust means 2 such as a turbo molecular pump, a cryopump, or a diffusion pump. In the vacuum chamber 3, there is provided a heating means 4 composed of a heat insulating material 41 surrounding a processing box, which will be described later, and a heating element 42 arranged inside the heat insulating material 41. The heat insulating material 41 is made of, for example, Mo, and the heating element 42 is an electric heater having a filament (not shown) made of Mo. The filament is energized from a power supply (not shown) and is insulated by resistance heating. The space 5 surrounded by the material 41 and in which the processing box is installed can be heated. In this space 5, for example, a mounting table 6 made of Mo is provided, and at least one processing box 7 can be mounted.

The processing box 7 includes a rectangular parallelepiped box portion 71 whose upper surface is opened and a lid portion 72 that is detachable from the upper surface of the opened box portion 71. A flange 72a bent downward is formed on the outer peripheral edge of the lid portion 72 over the entire circumference. When the lid portion 72 is attached to the upper surface of the box portion 71, the flange 72a is fitted to the outer wall of the box portion 71. Thus (in this case, a vacuum seal such as a metal seal is not provided), and a processing chamber 70 isolated from the vacuum chamber 3 is defined. Then, a predetermined pressure of the vacuum chamber 3 by actuating the evacuating means 2 (e.g., 1 × 10 -5 ^Pa) until the depressurizing substantially semi orders of magnitude higher pressure than the process chamber 70 is a vacuum chamber 3 (e.g., 5 × 10 ^{- The} pressure is reduced to ⁴ Pa). Thereby, the inside of the processing chamber 70 can be appropriately reduced to a predetermined vacuum pressure without the need for additional vacuum exhaust means.

  As shown in FIG. 3, in the box part 71 of the processing box 7, the sintered magnet S and the metal evaporation material v are stacked up and down with a spacer 8 interposed therebetween so that they are not in contact with each other. The spacer 8 is configured by assembling a plurality of wires 81 (for example, φ0.1 to 10 mm) in a lattice shape so as to have an area smaller than the cross section of the box portion 72, and the outer peripheral edge portion thereof is substantially perpendicular. Is bent upward. The height of the bent portion is set to be higher than the height of the sintered magnet S to be vacuum-steamed. In the present embodiment, the bent outer peripheral edge portion is a metal evaporation material installed on the upper side. The support piece 9 which secures space between v is comprised. A plurality of sintered magnets S are placed on the horizontal portion of the spacer 8 at regular intervals. In addition, it is preferable to mount so that a part with a large surface area among sintered magnets may oppose the metal evaporation material v.

  Here, as the metal evaporation material v, Dy and Tb that greatly improve the magnetocrystalline anisotropy of the main phase, or an alloy containing a metal that further enhances the coercive force such as Nd, Pr, Al, Cu, and Ga (see FIG. Dy and / or Tb mass ratio is 50% or more), and after the above metals are blended in a predetermined mixing ratio, for example, after being melted in an arc melting furnace, a plate having a predetermined thickness is formed. Yes. In this case, the metal evaporation material v has an area that is supported on the entire circumference of the support piece 9.

  And after installing the plate-shaped metal evaporation material v in the bottom face of the box part 71, the spacer 8 which arranged the sintered magnet S in parallel is mounted in the upper side, and also it is supported by the upper end of the support piece 9. FIG. In this manner, another plate-like metal evaporation material v is installed. In this way, the metal evaporation material v and the spacer 8 in which a plurality of sintered magnets S are juxtaposed are alternately stacked in a hierarchical manner up to the upper end of the processing box 7. Note that the metal evaporating material v can be omitted because the lid portion 72 is located close to the uppermost spacer 8.

  Thereby, the number of the sintered magnets S accommodated in one processing box 7 can be increased (loading capacity increases), and mass productivity can be improved. Further, as in the present embodiment, since a so-called sandwich structure in which the upper and lower sides of the sintered magnet S juxtaposed on the spacer 8 (same plane) is sandwiched between the plate-like metal evaporation materials v, all the sintering is performed in the processing chamber 70. When the metal evaporation material v is located in the vicinity of the magnet S and the metal evaporation material v is evaporated, the evaporated metal atoms are supplied to and adhered to the surface of each sintered magnet S. As a result, the effect of the vacuum vapor treatment of improving or recovering the magnetization and coercive force by diffusing Dy and Tb atoms into the crystal grain boundaries and / or crystal grain boundary phases of the sintered magnet is not impaired. In addition, a predetermined space is secured between the spacer 8 and the plate-like metal evaporating material v and the metal evaporating material v stacked immediately above the sintered magnet S. Contact can be prevented, and workability for storing the metal evaporation material v and the sintered magnet S in the processing box 7 is good.

The processing box 7 and the spacer 8 are, for example, Mo, W, Nb, V, Ta, or alloys thereof (including rare earth-added Mo alloys, Ti-added Mo alloys, etc.), CaO, Y ₂ O ₃ , or rare earth oxidation. It is preferable that the material is made of a material, or is formed by depositing these materials as a lining film on the surface of another heat insulating material. Thereby, it can prevent that the reaction product is formed on the surface by reacting with Dy and Tb.

  Further, as described above, when the metal evaporating material v and the sintered magnet S are stacked in the processing box 7 in a sandwich structure, the distance between the metal evaporating material v and the sintered magnet S is narrowed. If the metal evaporating material v is evaporated in such a state, there is a risk of being strongly influenced by the straightness of the evaporated metal atoms. That is, in the sintered magnet S, metal atoms are likely to locally adhere to the surface facing the metal evaporation material v, and the shadow of the wire 81 on the contact surface of the sintered magnet S with the spacer 8. It becomes difficult to supply Dy and Tb to the portion. For this reason, when the above-described vacuum vapor treatment is performed, the obtained permanent magnet M locally has a portion having a high coercive force and a portion having a low coercive force, and as a result, the squareness of the demagnetization curve is impaired.

  In the present embodiment, an inert gas introducing means is provided in the vacuum chamber 3. The inert gas introduction means has a gas introduction pipe 10 that leads to a space 5 surrounded by a heat insulating material 41, and the gas introduction pipe 10 communicates with a gas source of an inert gas via a mass flow controller (not shown). . During the vacuum vapor treatment, an inert gas such as He, Ar, Ne, Kr, N2 or the like is introduced in a constant amount. In this case, the introduction amount of the inert gas may be changed during the vacuum steam treatment (initially, the introduction amount of the inert gas is increased and then decreased or the introduction amount of the inert gas is initially reduced. Less, then more, or repeat these). The inert gas may be introduced, for example, after the metal evaporating material v starts evaporation or after reaching a set heating temperature, and may be introduced for a predetermined time during or around the set vacuum vapor processing time. In addition, when the inert gas is introduced, a valve 11 whose degree of opening and closing can be adjusted is provided in the exhaust pipe leading to the vacuum exhaust means 2 so that the partial pressure of the inert gas in the vacuum chamber 3 can be adjusted. preferable.

  As a result, the inert gas introduced into the space 5 is also introduced into the processing box 7. At this time, since the mean free path of the metal atoms of Dy and Tb is short, the inert gas evaporates in the processing box 7. The metal atoms diffused and the amount of metal atoms adhering directly to the surface of the sintered magnet S is reduced and supplied to the surface of the sintered magnet S from a plurality of directions. For this reason, even when the space | interval between the said sintered magnet S and the metal evaporation material v is narrow (for example, 5 mm or less), evaporated Dy and Tb wrap around and adhere to the shadow part of the wire 81. As a result, it is possible to prevent the metal atoms of Dy and Tb from being excessively diffused in the crystal grains and reducing the maximum energy product and the residual magnetic flux density. Furthermore, it can suppress that a part with a high coercive force exists locally and a low part, and can prevent that the squareness of a demagnetization curve is impaired.

  In the above embodiment, the case where the spacer 8 is configured by assembling a plurality of wires 81 in a lattice shape has been described as an example. However, the embodiment is not particularly limited as long as it allows passage of evaporated metal atoms. For example, the spacer 8 can be made of expanded metal formed by arranging rectangular punched holes at predetermined intervals on a plate material made of Mo or Nb and stretching the plate material. The expanded metal may be formed so that the opening ratio with respect to the surface area of the plate is 30 to 80% in consideration of strength.

  Thus, for example, when the spacer 8 that is an expanded metal made of Nb and having an opening ratio of about 60% is formed, it is compared with the case where the spacer 8 is configured by assembling Mo wire rods in a lattice shape with substantially the same opening ratio. The weight can be halved. As a result, when the same number of sintered magnets S and the plate-like metal evaporating material v are stacked one above the other with the spacers 8 interposed in the processing box 7, the weight is greatly reduced and the heat capacity is reduced. The cycle time can be shortened because the rate of temperature rise to the vacuum vapor treatment temperature, the vacuum chamber 3 after the vacuum vapor treatment, and the cooling rate of the magnet can be increased.

  Further, in the present embodiment, the case where the support piece 9 is integrally formed with the spacer 8 has been described as an example. However, the support piece 9 may be formed of other members, and the position where the support piece 9 is erected on the spacer 8 is not limited. I will not. In addition, the metal evaporating material v has been described as an example of a plate-like material, but the present invention is not limited to this, and the wire is assembled in a lattice shape on the upper surface of the sintered magnet placed on the spacer member. Alternatively, another spacer may be placed and a granular metal evaporation material may be spread on the spacer (see FIG. 4). Furthermore, although what used the support piece 9 was demonstrated to the example, you may make it stack both, without using the support piece 9. FIG. That is, after a spacer 8 configured by assembling a wire rod in a lattice shape is installed on a plate-shaped metal evaporation material v, a plurality of sintered magnets S are juxtaposed on the spacer 8 and the same configuration is formed thereon. Another spacer 8 having the above is installed, and a plate-shaped metal evaporation material v is further installed thereon. And it accumulates to the upper end part of the process box 7 in this way (refer FIG. 5). Thereby, the loading amount of the sintered magnet S to the processing box 7 can be further increased.

  Further, in the present embodiment, the case where the sintered magnet S and the metal evaporation material v are stored in the processing box 7 so as to supply evaporated metal atoms to substantially the entire surface of the sintered magnet S has been described as an example. In some cases, vacuum steam treatment may be performed only on a specific surface to which the reverse magnetic field of the sintered magnet S is applied. That is, in the segment magnet (sintered magnet) S1 provided between the rotating shaft constituting the motor and the stator core and arranged so as to form a cylindrical body as a whole, there is a case where the coercive force only needs to be increased only on the outer peripheral surface thereof. is there. In such a case, Dy and Tb, which are metal evaporation materials v, are scarce in terms of resources, so it is necessary to supply metal atoms only to the outer peripheral surface thereof.

  Therefore, as shown in FIGS. 6 and 7, when the metal evaporating material v and the segment magnet S1 are alternately stacked in the vertical direction with spacers interposed therebetween so that they do not contact each other, they are positioned on the inner surface side of the segment magnet S1. The spacer 12a to be formed may be made of a plate material, and the spacer 12b in contact with the outer peripheral surface of the segment magnet S1 may be made of a material that allows the passage of metal atoms as in the above embodiment. Thereby, one spacer 12a that prevents mutual contact between the metal evaporation material v and the sintered magnet S serves as a mask that prevents adhesion of metal atoms to one surface of the sintered magnet S. As a result, it is possible to easily realize a configuration in which metal atoms can be supplied only to a necessary surface, and further, parts such as a separate mask are not required, and the load can be increased.

  On the other hand, in a link-shaped magnet (ring magnet) S2, such as a radial anisotropic ring magnet or a polar anisotropic ring magnet, the outer peripheral surface is magnetized and used as a pole, so that only the outer peripheral surface has a high coercive force. In such a case, as shown in FIG. 8, a solid cylindrical support 13b erected at a location where a base in which a wire 13a made of Mo is assembled in a grid and a vertical and horizontal wire 13a intersect with each other, and What is necessary is just to use the jig | tool 13 comprised from these. Then, the ring magnet S2 is inserted into each support 13b having a diameter smaller than the inner diameter of the ring magnet S2 from above, and other metal atoms are allowed to pass so that the outer peripheral surfaces of the ring magnet S2 do not contact each other. Spacers 14 are arranged to accommodate the processing box 7. In this case, the jig 13 in which the ring magnet S2 is installed as described above may be stacked vertically in the processing box 7 via the spacer 8 having the same configuration as described above.

  Further, as shown in FIG. 9, the ring magnets S2 are arranged in parallel so that the outer peripheral surface thereof abuts against the spacer 8, and the inner diameter of each of the arranged ring magnets S2 is smaller than the inner diameter of the ring magnet S2. A solid cylindrical insert 15 may be inserted and arranged. In the same manner as described above, the metal evaporating material v, the spacer 8, the ring magnet S2, the spacer 8, and the metal evaporating material v are stacked up and down and stored in the processing box 7. In this case, the spacer 8 allows the metal to pass to the outer peripheral surface of the ring magnet S2 which is one side of the sintered magnet, while the insert 15 is in each ring magnet S which is the other surface of the sintered magnet S. It plays the role of a mask that prevents adhesion of metal atoms to the peripheral surface.

Next, vacuum vapor processing using the vacuum vapor processing apparatus 1 and using Dy as the metal evaporation material v will be described. As described above, the sintered magnet S and the plate-like metal evaporating material v are alternately stacked via the spacers 8 and are first installed in the box portion 71 (thereby, the sintered magnet S and the inside of the processing chamber 70). The metal evaporating material v is spaced apart). And after attaching the cover part 72 to the upper surface which the box part 71 opened, the process box 7 is installed on the table 6 in the space 5 enclosed by the heating means 4 in the vacuum chamber 3 (refer FIG. 1). The vacuum chamber 3 is evacuated and depressurized until it reaches a predetermined pressure (for example, 1 × 10 ⁻⁴ Pa) via the vacuum evacuation means 2 (the processing chamber 70 is evacuated to a pressure approximately half digit higher), When the vacuum chamber 3 reaches a predetermined pressure, the heating means 4 is operated to heat the processing chamber 70.

  When the temperature in the processing chamber 70 reaches a predetermined temperature under reduced pressure, the Dy in the processing chamber 70 is heated to substantially the same temperature as the processing chamber 70 to start evaporation, and a Dy vapor atmosphere is formed in the processing chamber 70. The At that time, the gas introduction means is operated to introduce the inert gas into the vacuum chamber 3 with a constant introduction amount. At this time, an inert gas is also introduced into the processing box 7, and the metal atoms evaporated in the processing chamber 70 are diffused by the inert gas.

  When Dy starts to evaporate, the sintered magnets S and Dy are arranged so as not to contact each other, so that the melted Dy directly adheres to the sintered magnet S in which the surface Nd-rich phase is melted. Absent. Then, the Dy atoms in the Dy vapor atmosphere diffused in the processing box are supplied from a plurality of directions, directly or repeatedly, toward the substantially entire surface of the sintered magnet S heated to substantially the same temperature as Dy. The adhered Dy is diffused into the crystal grain boundaries and / or crystal grain boundary phases of the sintered magnet S to obtain the permanent magnet M.

  Here, when Dy atoms in the Dy vapor atmosphere are supplied to the surface of the sintered magnet S so that a Dy layer (thin film) is formed, the Dy adhered and deposited on the surface of the sintered magnet S is recrystallized. When this occurs, the surface of the permanent magnet M is remarkably deteriorated (surface roughness is deteriorated), and Dy deposited and deposited on the surface of the sintered magnet S heated to substantially the same temperature during the treatment is dissolved and baked. It diffuses excessively in the grain boundary in the region close to the surface of the magnet S, and the magnetic properties cannot be improved or recovered effectively.

  That is, once a Dy thin film is formed on the surface of the sintered magnet S, the average composition of the sintered magnet surface S adjacent to the thin film becomes a Dy rich composition. The surface of the magnet S is melted (that is, the main phase is melted and the amount of the liquid phase is increased). As a result, the vicinity of the surface of the sintered magnet S melts and collapses, and the unevenness increases. In addition, Dy excessively penetrates into the crystal grains together with a large amount of liquid phase, and the maximum energy product and the residual magnetic flux density showing the magnetic characteristics are further lowered.

In the present embodiment, when the metal evaporation material v is Dy, in order to control the evaporation amount of Dy, the heating means 4 is controlled so that the temperature in the processing chamber 70 is 800 ° C. to 1050 ° C., preferably 850 ° C. It was decided to set in the range of ˜950 ° C. (for example, when the processing chamber temperature is 900 ° C. to 1000 ° C., the saturated vapor pressure of Dy is about 1 × 10 ⁻² to 1 × 10 ⁻¹ Pa).

  When the temperature in the processing chamber 70 (and thus the heating temperature of the sintered magnet S) is lower than 800 ° C., the diffusion rate of Dy atoms adhering to the surface of the sintered magnet S to the grain boundaries and / or grain boundary layers is increased. It becomes slow and cannot be uniformly distributed by diffusing into the crystal grain boundary and / or the grain boundary phase of the sintered magnet before the thin film is formed on the surface of the sintered magnet S. On the other hand, at a temperature exceeding 1050 ° C., the vapor pressure of Dy increases, and there is a risk that Dy atoms in the vapor atmosphere are excessively supplied to the surface of the sintered magnet S. Further, there is a possibility that Dy diffuses into the crystal grains, and when Dy diffuses into the crystal grains, the magnetization in the crystal grains is greatly reduced, so that the maximum energy product and the residual magnetic flux density are further lowered. At the same time, the degree of opening and closing of the valve 11 was changed so that the partial pressure of the inert gas introduced into the vacuum chamber 3 was 3 Pa to 50000 Pa. At a pressure lower than 3 Pa, Dy and Tb are locally attached to the sintered magnet S, and the squareness of the demagnetization curve is deteriorated. Further, at a pressure exceeding 50000 Pa, the evaporation of the metal evaporation material v is suppressed, and the processing time becomes excessively long.

  Thereby, the partial pressure of the inert gas such as Ar is adjusted to control the evaporation amount of Dy, and the Dy atoms evaporated by the introduction of the inert gas are diffused in the processing box, so that the sintered magnet S can be diffused. Sintering of Dy atoms on the entire surface while suppressing the supply amount of Dy atoms and heating the sintered magnet S in a predetermined temperature range increases the diffusion rate, thereby sintering. Dy atoms adhering to the surface of the magnet S are efficiently diffused to the grain boundaries and / or grain boundary phases of the sintered magnet S before being deposited on the surface of the sintered magnet S to form a Dy layer (thin film). It can be evenly distributed (see FIG. 1). As a result, it is possible to prevent the surface of the permanent magnet M from being deteriorated, to suppress excessive diffusion of Dy into the grain boundary in the region close to the surface of the sintered magnet, and to form a Dy rich phase (Dy) in the grain boundary phase. In addition, the diffusion and diffusion of Dy only in the vicinity of the surface of the crystal grains effectively improves or recovers the magnetization and the coercive force. A permanent magnet M excellent in unnecessary productivity can be obtained.

  In addition, the metal atoms evaporated in the processing box 7 are diffused and present, and the sintered magnet S is placed on a spacer 8 in which thin wires 81 are assembled in a lattice shape. Even when the distance from the metal evaporation material v is narrow, the evaporated Dy and Tb wrap around and adhere to the shadowed portion of the wire 81. As a result, it is possible to suppress the presence of locally high and low coercivity portions and prevent the squareness of the demagnetization curve from being impaired even if the vacuum vapor treatment is applied to the sintered magnet. High mass productivity can be achieved.

  Finally, after performing the above process for a predetermined time (for example, 4 to 48 hours), the operation of the heating unit 4 is stopped and the introduction of the inert gas by the gas introduction unit is temporarily stopped. Subsequently, an inert gas is again introduced (100 kPa), and evaporation of the metal evaporation material v is stopped. Note that the evaporation may be stopped by increasing only the introduction amount without stopping the introduction of the inert gas. Then, the temperature in the processing chamber 70 is temporarily lowered to 500 ° C., for example. Subsequently, the heating means 4 is operated again, the temperature in the processing chamber 70 is set in the range of 450 ° C. to 650 ° C., and heat treatment is performed to further improve or recover the coercive force. Then, it is rapidly cooled to approximately room temperature, and the processing box 7 is taken out from the vacuum chamber 3.

  In this embodiment, the example using Dy as the metal evaporation material has been described as an example. However, when Tb having a low vapor pressure is used in the heating temperature range of the sintered magnet S that can increase the optimum diffusion rate, the processing chamber 70 is used. May be heated in the range of 900 ° C to 1150 ° C. At a temperature lower than 900 ° C., the vapor pressure that can supply Tb atoms to the surface of the sintered magnet S is not reached. On the other hand, at a temperature exceeding 1150 ° C., Tb is excessively diffused in the crystal grains, thereby reducing the maximum energy product and the residual magnetic flux density.

Further, in order to remove dirt, gas and moisture adsorbed on the surface of the sintered magnet S before diffusing Dy and Tb to the crystal grain boundaries and / or crystal grain boundary phases, the vacuum chamber 3 is provided via the vacuum exhaust means 11. Is reduced to a predetermined pressure (for example, 1 × 10 ⁻⁵ Pa), and the processing chamber 70 is decreased to a pressure (for example, 5 × 10 ⁻⁴ Pa) approximately half an order higher than that of the vacuum chamber 3 and then held for a predetermined time. It may be. At that time, the heating means 4 may be operated to heat the inside of the processing chamber 70 to, for example, 300 ° C. and hold it for a predetermined time.

  Further, in the present embodiment, the description has been given of the case in which the lid 72 is attached to the upper surface of the box portion 71 to constitute the processing box 7, but the processing chamber 7 is isolated from the vacuum chamber 3 and the vacuum chamber 3 is decompressed. For example, after the metal evaporation material v and the sintered magnet S are accommodated in the box portion 71, the upper surface opening thereof is made of, for example, a Mo foil. You may make it cover with. On the other hand, for example, the processing chamber 70 may be sealed in the vacuum chamber 3 and may be configured to be maintained at a predetermined pressure independently of the vacuum chamber 3.

  As the sintered magnet S, the smaller the oxygen content, the faster the diffusion rate of Dy and Tb to the crystal grain boundaries and / or the crystal grain boundary phases, so the oxygen content of the sintered magnet S itself is 3000 ppm. Hereinafter, it is preferably 2000 ppm or less, more preferably 1000 ppm or less.

In Example 1, a permanent magnet M was obtained by subjecting the next sintered magnet S to vacuum vapor treatment using the vacuum vapor treatment apparatus 1 shown in FIG. As the sintered magnet S, industrial pure iron, metallic neodymium, low carbon ferroboron, electrolytic cobalt, pure copper as a raw material, with a composition (weight%),
25Nd-7Pr-1B-0.05Cu-0.05Ga-0.05Zr-Bal. Fe (sample 1),
7Nd-25Pr-1B-0.03Cu-0.3Al-0.1Nb-Bal. Fe (sample 2),
28Nd-1B-0.05Cu-0.01Ga-0.02Zr-Bal. Fe (sample 3),
27Nd-2Dy-1B-0.05Cu-0.05Al-0.05Nb-Bal. Fe (sample 4),
29Nd-0.95B-0.01Cu-0.02V-0.02Zr-Bal. Fe (sample 5),
32Nd-1.1B-0.03Cu-0.02V-0.02Nb-Bal. Fe (sample 6),
32Nd-1.1B-0.03Cu-0.02V-0.02Nb-Bal. Fe (sample 7),
Then, vacuum induction melting was performed, and a flaky ingot having a thickness of about 0.3 mm was obtained by a strip casting method. Next, it was roughly pulverized by a hydrogen pulverization step, and then finely pulverized by, for example, a jet mill pulverization step to obtain an alloy raw material 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 sintered magnet was processed into a shape of 2 × 40 × 40 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.

Next, using the vacuum vapor processing apparatus 1 shown in FIG. 1, vacuum vapor treatment was performed on the sintered magnets S produced as described above (10 pieces each). In this case, Dy (99%) formed in a plate shape with a thickness of 0.5 mm is used as the metal evaporating material v, and the metal evaporating material v and the sintered magnet S are stored in the W processing box 7. did. Then, after the pressure in the vacuum chamber 3 reaches 10 ⁻⁴ Pa, the heating means 4 is operated, the temperature in the processing chamber 70 is set to 800 ° C. to 950 ° C., the processing time is set to 3 to 15 hours, and the above Processed.

  FIG. 10 shows the distance between the sintered magnet S and the metal evaporation material v in the processing box 2, the gas type of the inert gas introduced during the vacuum vapor processing, and the partial pressure of the inert gas at that time. Is a table showing the optimum magnetic characteristics (measured by a BH curve tracer) and the processing conditions when the optimum processing conditions are obtained by changing the above and the permanent magnet is obtained. Here, the squareness ratio (%) in the table is the magnitude of the demagnetizing field necessary for the magnetization value to decrease to a certain ratio in the second quadrant of the square demagnetization curve. In the example, the magnitude of the magnetic field when it is reduced by 10% is represented by Hk, and Hk / iHc is represented in 100 fractions.

  According to this, when the interval between the sintered magnet S and the metal evaporation material v in the processing box 7 is 10 mm, the coercive force (iHc) can be increased without introducing the inert gas. I understand. On the other hand, when the interval is 5 mm or less, when the vacuum vapor treatment is performed without introducing the inert gas, the maximum energy product showing the magnetic characteristics becomes about half and the squareness ratio is 74% or less. On the other hand, it can be seen that a high squareness ratio of 98% or more is obtained if a predetermined inert gas is appropriately introduced. Accordingly, in order to increase the productivity by reducing the interval between the sintered magnet S and the metal evaporation material v in the processing box 7 and increasing the load of the sintered magnet S, the introduction of an inert gas is required. It turns out that is effective.

Sectional drawing which illustrates typically the cross section of the permanent magnet produced by this invention. Sectional drawing which shows schematically the vacuum processing apparatus which implements the process of this invention. The perspective view explaining typically loading of the sintered magnet and metal evaporation material to a processing box. The perspective view explaining typically loading of the sintered magnet and metal evaporation material to the processing box concerning a modification. The perspective view explaining typically loading of the sintered magnet and metal evaporation material to the processing box concerning other modifications. Sectional drawing which illustrates typically the vacuum vapor process to the sintered magnet (segment magnet) which concerns on another modification. FIG. 7 is a perspective view schematically illustrating the loading of a sintered magnet (segment magnet) and a metal evaporation material on the processing box shown in FIG. 6. The perspective view explaining typically loading of the sintered magnet (ring magnet) and metal evaporation material to the processing box concerning other modifications. Furthermore, the perspective view explaining typically loading of the sintered magnet (ring magnet) and metal evaporation material to the process box which concerns on another modification. 2 is a table showing the magnetic characteristics of the permanent magnet produced in Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum vapor processing apparatus 2 Vacuum exhaust means 3 Vacuum chamber 4 Heating means 7 Processing box 71 Box part 72 Cover body 8 Spacer 81 Wire 9 Supporting piece 10 Gas introduction pipe (gas introduction means)
11 Valve S Sintered magnet M Permanent magnet v Metal evaporation material

Claims (4)

A metal evaporation material containing at least one of Dy and Tb and a ring magnet are stored in the processing box, and after the processing box is placed in a vacuum chamber, the processing box is heated to a predetermined temperature in a vacuum atmosphere. A method for producing a permanent magnet in which a metal evaporation material is evaporated and adhered to a sintered magnet, and the adhered metal atoms of Dy and Tb are diffused into the crystal grain boundary and / or the grain boundary phase of the sintered magnet. ,
It has a jig composed of a base with wire rods assembled in a lattice shape and supports that stand upright at the intersections of vertical and horizontal wires, and each ring magnet is inserted into each support member from above A method of manufacturing a permanent magnet, wherein a spacer that allows passage of metal atoms is arranged so that the ring magnets do not contact each other and is stored in a processing box . 2. The method of manufacturing a permanent magnet according to claim 1, wherein jigs in which ring magnets are installed are stored in the processing box by being stacked up and down via a plate-shaped metal evaporation material . The processing box can be inserted into and removed from the vacuum chamber , and includes a box part having an upper surface opened and a lid part detachably attached to the opened upper surface. The method of manufacturing a permanent magnet according to claim 1 or 2, wherein the inside of the processing box is depressurized as the vacuum chamber is depressurized by being actuated. 4. The method of manufacturing a permanent magnet according to claim 1 , wherein an inert gas is introduced into the vacuum chamber while the metal evaporating material is evaporating.