JP4605437B2 - Rare earth magnet manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a rare earth magnet, and more particularly to a technique for efficiently recovering a surface property degradation layer.

  Rare earth sintered magnets, such as Nd-Fe-B based sintered magnets, are known as high performance magnets with excellent magnetic properties, and are used for magnetic resonance imaging diagnostic (MRI) magnetic circuits and hard disk drives (HDD). In addition to motors, it is widely applied. And since a Nd-Fe-B system sintered magnet has the highest magnetic characteristic in a practical magnet, it has contributed to size reduction of these applied products.

  However, this kind of rare earth sintered magnet has a tendency to deteriorate the magnetic properties by machining such as cutting and polishing, and there is a problem to solve it. In particular, the magnetic characteristics of a small magnet are significantly reduced, which is a major obstacle in, for example, advancing miniaturization of mobile devices and high performance of micromachines. In the vicinity of the surface of the magnet due to machining, the influence of the processing is on the order of several tens to 200 μm, and in a magnet having a large surface area and a small volume, the proportion of the affected surface portion is increased, and the magnetic properties are reduced. Appears prominently.

  Thus, conventionally, attempts have been made to recover the magnetic characteristics by taking various measures against the deterioration of the magnetic characteristics due to such machining (for example, Patent Document 1, Patent Document 2, Non-Patent Document 1, etc.). See).

Patent Document 1 discloses a method of recovering a work-deteriorated layer to a normal structure by performing an aging treatment after sintering and processing into a final shape. Patent Document 2 discloses a method for improving magnetic characteristics (residual magnetic flux density Br and maximum energy product BH) by repeatedly performing heat treatment and grinding of the surface of the sintered body after heat treatment. Non-Patent Document 1 discloses a method for improving characteristics by surface modification by depositing Dy metal by sputtering and then performing heat treatment (aging treatment).
JP 61-140108 A JP-A-7-37742 27th Annual Meeting of the Japan Society of Applied Magnetics (2003), p386

  However, with only the aging treatment (heat treatment) described in Patent Document 1 and Patent Document 2, the effect of recovering sufficient magnetic properties is not obtained as the thickness becomes particularly thin. Further, even the method described in Non-Patent Document 1 can be expected to recover magnetic properties such as squareness to some extent, but it is not always sufficient. There are also many problems in terms of time required for recovery and stable recovery.

  The present invention has been proposed in view of such a conventional situation, and provides a technique for sufficiently recovering a processing deteriorated layer by a practical and simple method even in a thin-walled magnet or the like. It is the purpose. That is, the present invention provides a method for producing a rare earth magnet capable of stably recovering magnetic properties in a short time and capable of producing a rare earth magnet having high magnetic properties as a final product. Objective.

In order to achieve the above-mentioned object, the method for producing a rare earth magnet of the present invention comprises forming a film mainly composed of a rare earth element on the surface of a magnet body, performing a two-step heat treatment, and performing the first step at 500 °. As described above, heat treatment is performed at a temperature lower than the melting point of the film, heat treatment is performed at a temperature not lower than the melting point of the film and not higher than 1000 ° C. in the second stage, and the heat treatment time for each stage is 10 minutes to 1 hour .

  By coating the magnet body with a coating mainly composed of rare earth elements and applying a heat treatment for recovery, it is formed on the surface of the magnet body by machining or the like due to the surface modification action of the rare earth elements contained in the coating. The deteriorated processing layer is restored to the normal structure, and the properties are restored. At this time, by performing the heat treatment in two stages and optimizing the heat treatment temperature in each stage, quick characteristic recovery and stable characteristic recovery are realized.

  According to the present invention, it is possible to efficiently recover a decrease in magnetic properties due to a processing deteriorated layer, and in terms of squareness, coercive force, maximum energy product, etc., the magnetic properties are comparable to, for example, the magnetic properties before processing. It is possible to provide a rare earth magnet. In addition, according to the manufacturing method of the present invention, it is possible to efficiently and stably modify the surface of the work deterioration layer in a short time, and it is possible to greatly reduce the manufacturing time and manufacturing cost.

  Hereinafter, a method for producing a rare earth magnet to which the present invention is applied will be described in detail.

First, in the present invention, a rare earth magnet as a production control is a rare earth sintered magnet mainly composed of a rare earth element, a transition metal element and boron, for example, an NdFeB rare earth sintered magnet or the like as a magnet body. Here, the magnet composition of the magnet body may be arbitrarily selected according to the purpose. For example, R-T-B (one or more of rare earth elements including R = Y, T = one or more of transition metal elements essential to Fe or Fe and Co, B = boron) system When a rare earth sintered magnet is used, in order to obtain a rare earth sintered magnet having excellent magnetic properties, the sintered magnet composition has a rare earth element R of 27.0 to 32.0 wt% and boron B of 0. It is preferable that the blending composition is 5 to 2.0% by weight and the balance is substantially the transition metal element T (for example, Fe). When the amount of the rare earth element R is less than 27.0% by weight, α-Fe or the like that is soft magnetic precipitates, and the coercive force decreases. Conversely, when the rare earth element R exceeds 32.0% by weight, the amount of the R-rich phase increases and the corrosion resistance deteriorates, and the volume ratio of the R ₂ T ₁₄ B crystal grains as the main phase decreases. The residual magnetic flux density is reduced. Further, when boron B is less than 0.5% by weight, a high coercive force cannot be obtained. Conversely, if boron B exceeds 2.0% by weight, the residual magnetic flux density tends to decrease.

In the composition, the rare earth element R is a rare earth element including Y, that is, one selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu, or 2 or more types. Among these, Nd and Pr are preferably Nd and Pr because the balance of magnetic properties is good and they are abundant and relatively inexpensive. Dy ₂ Fe ₁₄ B and Tb ₂ Fe ₁₄ B compounds have a large anisotropic magnetic field and are effective in improving the coercive force Hcj.

  Furthermore, the rare earth sintered magnet may be an R-TBM type rare earth sintered magnet by adding an additive element M. In this case, examples of the additive element M include Al, Ga, Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W, V, Zr, Ti, Hf, and Mo. A seed | species or 2 or more types can be selected and added. For example, the addition of Nb, Zr, W or the like, which is a refractory metal, has an effect of suppressing crystal grain growth. Of course, it is needless to say that the composition of the magnet element body is not limited to these compositions, and can be applied to all conventionally known rare earth magnet compositions.

  The magnet body is made into a predetermined size by machining such as cutting or polishing after sintering, but the present invention is highly effective when applied to a magnet body having a thickness of 2 mm or less. In particular, when applied to a magnet element having a thickness of 1 mm or less, a more remarkable effect can be expected.

  The rare earth magnet produced according to the present invention is obtained by coating the magnet body with a coating mainly composed of rare earth elements and performing a recovery treatment. Here, the rare earth element contained in the coating is preferably at least one selected from Nd, Pr, Dy, and Tb. The metal constituting the coating is preferably a rare earth-rich alloy containing a large amount of the rare earth element, and may be a binary alloy or a ternary or higher alloy. By this coating and recovery treatment with the coating, the ratio of rare earth elements in the vicinity of the surface of the magnet body increases, the work-deteriorated layer in the vicinity of the surface is modified, and the magnetic characteristics are greatly improved.

  Next, the manufacturing method of the rare earth magnet of this invention is demonstrated. In the rare earth magnet of the present invention, the rare earth sintered magnet as the magnet body is manufactured by a powder metallurgy method. Hereinafter, a method for producing a rare earth sintered magnet by powder metallurgy will be described.

  FIG. 1 shows an example of a process for producing a rare earth sintered magnet by a powder metallurgy method, and a subsequent processing process. This manufacturing process basically includes an alloying step 1, a coarse pulverizing step 2, a fine pulverizing step 3, a magnetic field forming step 4, a sintering step 5, a machining step 6, a film forming step 7, and a first stage heat treatment. 8, second stage heat treatment 9, aging step 10, and grinding step 11. In order to prevent oxidation, most of the steps after sintering are performed in a vacuum or in an inert gas atmosphere (in a nitrogen atmosphere, an Ar atmosphere, etc.).

  In the alloying step 1, a raw material metal or alloy is blended according to the raw material alloy composition, melted in an inert gas, for example, Ar atmosphere, and cast into an alloy. As a casting method, a strip casting method (continuous casting method) in which molten high-temperature liquid metal is supplied onto a rotating roll and an alloy thin plate is continuously cast is preferable from the viewpoint of productivity and the like. As the raw material metal (alloy), pure rare earth elements, rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. When cast as an ingot, solution treatment may be performed as necessary for the purpose of eliminating solidification segregation. As a condition for the solution treatment, for example, it is kept in a 700 to 1200 ° C. region for 1 hour or more under vacuum or Ar atmosphere.

  In the coarse pulverization step 2, the previously cast raw alloy thin plate, ingot or the like is pulverized to a particle size of about several hundred μm. As the pulverizing means, a stamp mill, a jaw crusher, a brown mill, or the like can be used. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen and embrittlement.

  After the aforementioned coarse pulverization step 2 is completed, a pulverization aid is usually added to the coarsely pulverized raw material alloy powder. As the grinding aid, for example, fatty acid compounds can be used, and in particular, by using fatty acid amide as the grinding aid, a rare earth sintered magnet having good magnetic properties, particularly high orientation and high magnetization. Can be obtained. The addition amount of the grinding aid is preferably 0.03 to 0.4% by weight. If the addition amount of the grinding aid is less than 0.03% by weight, the effect on the magnetic properties of the lubricant cannot be sufficiently obtained. If the addition amount is 0.4% by weight or less, the residual after sintering The amount of carbon can be effectively reduced, which is effective in improving the magnetic properties of the rare earth sintered magnet.

  After the coarse pulverization step 2, a fine pulverization step 3 is performed. The fine pulverization step 3 is performed using, for example, an airflow pulverizer. The conditions for fine pulverization may be appropriately set according to the airflow pulverizer to be used, and the raw material alloy powder is finely pulverized until the average particle size becomes about 1 to 10 μm, for example, 3 to 6 μm. A jet mill or the like is suitable as the airflow pulverizer. A jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, accelerates powder particles by this high-speed gas flow, and collides powder particles with each other. Or, it is a method of crushing by generating a collision with a collision plate or a container wall. Jet mills are generally classified into jet mills that use fluidized beds, jet mills that use vortex flow, jet mills that use impingement plates, and the like. Among these jet mills, a jet mill using a fluidized bed and a jet mill using a vortex are preferable, and a jet mill using a fluidized bed is particularly preferable. For example, although the specific gravity of the raw material alloy powder and the grinding aid differ greatly, in the fluidized bed and in the vortex, the grinding and mixing are performed well regardless of the difference in specific gravity, and the difference in specific gravity is particularly problematic in the fluidized bed. It is because it does not become.

  After the pulverizing step 3, in the forming step 4 in the magnetic field, the raw material alloy fine powder is formed in the magnetic field. Specifically, the raw material alloy fine powder obtained in the fine pulverization step 3 is filled in a mold in which an electromagnet is arranged, and is molded in a magnetic field with a crystal axis oriented by applying a magnetic field. The forming in the magnetic field may be either a vertical magnetic field forming in which the forming pressure and the magnetic field direction are parallel, or a horizontal magnetic field forming in which the forming pressure and the magnetic field direction are orthogonal to each other. Further, a pulse power source and an air-core coil can be employed as the magnetic field applying means. The forming in the magnetic field may be performed at a pressure of about 100 to 200 MPa in a magnetic field of 700 to 1300 kA / m, for example.

  Next, the molded body formed by the molding step in the magnetic field is sintered, but it is preferable to perform a debinding process in the debinding step prior to sintering. This binder removal process is a process for removing the lubricant added in the pulverization process and contained in the molded body, and by removing the binder, carbon remaining as a carbide, oxide, etc. after sintering. And the remaining amount of oxygen can be reduced.

  Next, in the sintering step 5, sintering is performed. That is, after forming the raw material alloy fine powder in a magnetic field, the formed body (pre-sintered body) subjected to the binder removal treatment is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, and the difference of a particle size and a particle size distribution, for example, what is necessary is just to sinter at 1000-1150 degreeC for about 5 hours. The heating method is arbitrary such as resistance heating and high frequency induction heating.

  The rare earth sintered magnet that has undergone the sintering process or the subsequent aging process is processed into a predetermined size by machining such as cutting, polishing, sand blasting, and barrel machining in the machining process 6. The machining method is arbitrary, and examples of the cutting method include a wire saw and electric discharge machining. The processing size of the magnet body is also arbitrary, but the thickness of the processing degradation layer is almost constant, so the thickness of the processing size of the magnet body is not easily affected. Be susceptible. When machining is performed so that the thickness is 2 mm or less, particularly 1 mm or less, the effect of the recovery process described later is large.

  A rare earth sintered magnet machined to a predetermined size by machining is used as a magnet body, and this is used as a rare earth magnet. However, a machined magnet body has a process-deteriorated layer formed on its surface, resulting in reduced magnetic properties. Is seen. Therefore, in the present invention, in the next film formation step 7, a film mainly composed of rare earth elements is formed, and further, in the recovery process, that is, in the first stage heat treatment process 8 and the second stage heat treatment process 9, the recovery process is performed. By doing so, recovery of magnetic properties is aimed at.

  The coating can be formed by any method. For example, it can be formed by a physical vapor deposition method (PVD method) such as vapor deposition or sputtering, a chemical vapor deposition method (CVD method), a dipping method, or the like. The physical vapor deposition method is described in detail in the aforementioned Non-Patent Document 1. Hereinafter, formation of a film by a CVD method and formation of a film by a dipping method will be described.

  First, in the CVD method, energy is applied to a gas containing a raw material by heat or light, or plasma is generated at a high frequency, so that the raw material is radicalized and rich in reactivity, and is adsorbed on the substrate. accumulate. As the CVD method, for example, a material such as a thermal CVD for increasing the temperature, a light CVD for irradiating light to promote a chemical reaction or thermal decomposition, a plasma CVD for exciting a gas into a plasma state, a tungsten hot wire, etc. Various types of CVD methods such as Cat-CVD for catalytically decomposing gas with high efficiency are known, but any method can be arbitrarily employed in the present invention.

  FIG. 2 shows a schematic configuration of an example of a CVD apparatus. The CVD apparatus includes a vacuum chamber 21 that forms a film formation space, a vacuum exhaust mechanism 22 that makes the inside of the vacuum chamber 21 a predetermined degree of vacuum, and a source gas supply unit 23 that supplies a source gas into the vacuum chamber 21. Is done. Although not shown, the vacuum chamber 21 is provided with, for example, a heating means, a light source, a high frequency power supply, a hot wire, etc. according to the CVD method.

  As the source gas supply means 23, a tank, a cylinder or the like filled with the source gas is usually used. However, in the present invention, a solid rare earth compound is vaporized at room temperature to form a film. A raw material container 26 containing a carrier gas source 24 and a rare earth compound 25 is used. The raw material container 26 is provided with heating means, and the carrier gas is supplied while heating the raw material container 26, whereby the rare earth compound 25 is vaporized and introduced into the vacuum chamber 21 through the shower head 27. The introduced rare earth compound is decomposed in the vacuum chamber 21 and deposited on the surface of the magnet body 28 installed in the vacuum chamber 21 to form a CVD film. When the CVD film is a binary alloy, or a ternary or higher alloy, the source gas supply means 23 are installed in parallel by the number of metals constituting the CVD film, and the compound of each metal element is supplied to the source container 26. Housed inside. The source gas supply means 23 is provided with a flow meter 29 and an adjustment valve 30 so that the supply amount of the source gas can be controlled.

  When forming the CVD film, it is necessary to cover the entire surface of the magnet body 28 with a uniform CVD film. Therefore, it is preferable to perform film formation by CVD while stirring the magnet body 28 in the vacuum chamber 21 by rotation, vibration, or the like.

Examples of the rare earth compound used as a raw material include a β-diketone-based rare earth element organometallic complex. Specific examples of the compound include general formulas R (DPM) ₃ , R (HFA) ₃ , R (FOD) _{3 and the} like. In the above general formula, R is a rare earth element, and DPM is 2,2,6,6-tetramethyl-1,3,5-heptanedione (2,2,6,6-tetramethyl-1,3,5- heptanedione), HFA is 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (1,1,1,5,5,5, -hexafluoro-2,4-pentanedione), FOD 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione (1,1,1,2,2,3,3-heptafluoro-7,7 -dimethyl-4,6-octanedione). Alternatively, as the β-diketone-based rare earth element organometallic complex, an organic rare earth complex using 6-ethyl-2,2-dimethyl-3,5-octanedione as a ligand of a rare earth element can be used.

  The rare earth compound is heated and vaporized at a temperature of hundreds of degrees Celsius or higher, and a vapor containing this is supplied into the vacuum chamber 21. Alternatively, these rare earth compounds can be dissolved in a solvent such as tetrahydrofuran (THF) to form a solution, which can be supplied into the vacuum chamber 21 using a liquid mass flow controller or sprayed from a nozzle.

When the CVD film is a binary alloy, or a ternary or higher alloy, it is necessary to use a compound of another metal element as a raw material, but also in the case of a metal element other than rare earth elements such as Fe, By using various existing organometallic compounds such as β-diketone organometallic complexes such as Fe (DPM) ₃ , raw materials can be supplied.

  In the above-described CVD method, the composition of the CVD film formed can be controlled by controlling the flow rate of the source gas. Therefore, it is possible to give a distribution to the composition of the CVD film by utilizing this. As described above, in the CVD film, at least one concentration selected from Nd and Pr is high in the inner portion in contact with the magnet body, and Dy and Tb are selected in the outer portion on the opposite side. By providing the composition distribution so that at least one concentration becomes high, the amount of Dy and Tb used can be reduced, and the manufacturing cost can be suppressed.

  In order to give such a composition distribution to the CVD film, first, at least one rare earth compound selected from Nd and Pr is supplied as a source gas, and a CVD film mainly composed of Nd or Pr is formed. Next, the source gas is switched, at least one rare earth compound selected from Dy and Tb is supplied as a source gas, and a CVD film mainly composed of Dy or Tb is formed. Thereby, a CVD film having the composition distribution is formed.

  On the other hand, the dipping process is an extremely simple technique because it is sufficient to immerse the magnet body in a molten alloy mainly composed of rare earth elements. The molten alloy used is mainly composed of rare earth elements, but it may be a molten rare earth element alone, or a binary alloy containing rare earth elements, or a molten alloy of ternary or higher alloys. Also good. However, in order to obtain the effect by the modification of the work deterioration layer, it is preferable to contain 50 atom% or more of rare earth elements. Moreover, it is preferable that the ratio of the rare earth element contained in the molten alloy is larger than the ratio of the rare earth element contained in the magnet body.

  Further, if the melting point of the molten alloy is too high, the melting point approaches the sintering temperature of the magnet body and may deteriorate the characteristics of the magnet body, and therefore it is preferably set to 1000 ° C. or lower. Therefore, it is also necessary to set the composition of the molten alloy from the viewpoint of this melting point. For example, FIG. 3 shows a Dy—Fe phase diagram, and FIG. 4 shows a Nd—Fe phase diagram. In the Dy-Fe system, the melting point is lowered to 890 ° C. when Dy is 70 atomic%, and a melting point of 1000 ° C. or less is achieved when Dy is 65 atomic% to 77 atomic%. In the Nd—Fe system, Nd is 78 atomic% and the melting point is 685 ° C., and Nd is 55 atomic% or more and the melting point is 1000 ° C. or less.

  The dipping time in the dipping process is about 10 minutes to 1 hour. If the dipping time is too short, the surface modification effect may be insufficient. If the dipping time is too long, the productivity is lowered and the thermal influence on the magnet body may be increased. If the dipping temperature and dipping time are optimized, the aging treatment can be performed, and the manufacturing process can be further simplified.

  After a film is formed on the surface of the magnet body by any of the above methods, the surface of the magnet body is modified in a recovery process. This recovery process is performed by, for example, heat treatment. In the present invention, the heat treatment for the recovery process is a two-stage heat treatment at different temperatures. What is important here is the temperature setting at each stage, which is set so that the second stage heat treatment temperature is higher than the first stage heat treatment temperature.

  Specifically, heat treatment is performed at a temperature at which a solid phase reaction proceeds in the first stage, and heat treatment is performed at a temperature at which a liquid phase is generated in the second stage. Alternatively, the first stage is heat-treated at a temperature lower than the melting point of the film, and the second stage is heat-treated at a temperature higher than the melting point of the film.

  For example, in the Dy-Fe phase diagram shown in FIG. 3 and the Nd-Fe phase diagram shown in FIG. 4, only the liquid phase is present in the region above the melting point curve showing the melting point of each composition. In a region where the temperature is lower, a solid phase or a mixed phase of a solid phase and a liquid phase is obtained. The Dy—Fe system has the lowest melting point of 890 ° C. when Dy is 70 atomic%, and the Nd—Fe system has the lowest melting point of 685 ° C. with Nd of 78 atomic%. Therefore, in the case of Dy—Fe system, if it is less than 890 ° C., and in the case of Nd—Fe system, if it is less than 685 ° C., only a solid phase is obtained regardless of the composition.

  As described above, when the heat treatment is performed at the temperature at which the solid phase reaction proceeds in the first stage and the heat treatment is performed at the temperature at which the liquid phase is generated in the second stage, the temperature is less than 890 ° C. for the Dy-Fe system and 685 for the Nd—Fe system. The first heat treatment is performed at a temperature lower than 0 ° C., and the second heat treatment is performed at 890 ° C. or more for the Dy—Fe system and 685 ° C. or more for the Nd—Fe system. In the first heat treatment, the film formed on the surface of the magnet element body maintains a solid state, and diffusion of rare earth elements constituting the film into the magnet element body is performed by a so-called solid phase reaction. In the second heat treatment, when the temperature is lower than the melting point curve, the rare earth element constituting the coating is diffused into the magnet body in a mixed phase state of the solid phase and the liquid phase. When the heat treatment temperature in the second stage is higher than the melting point curve, the rare earth element constituting the coating is diffused into the magnet body in the liquid phase.

  On the other hand, when heat treatment is performed at a temperature lower than the melting point of the film in the first stage and heat treatment is performed at a temperature higher than the melting point of the film in the second stage, the first heat treatment is less than 890 ° C. in Dy-Fe system, Nd— When it is performed at a temperature of less than 685 ° C. in an Fe system, the rare earth element constituting the coating is diffused into the magnet body by a solid phase reaction, and in the second heat treatment, the heat treatment is performed at a temperature higher than the melting point of the coating. Therefore, diffusion of rare earth elements constituting the coating in a liquid phase state into the magnet element body is performed. In a composition other than the eutectic composition, when the first stage heat treatment is performed at a temperature of 890 ° C. or higher for the Dy—Fe system and 685 ° C. or higher for the Nd—Fe system, Diffusion of the rare earth elements constituting the coating into the magnet body is performed in a mixed phase with the liquid phase.

  However, in any case, the heat treatment temperature in the first stage is preferably 500 ° C. or higher. If the first-stage heat treatment temperature is less than 500 ° C., the solid-phase reaction does not proceed, and the predetermined effect may not be obtained. Further, the heat treatment temperature in the second stage is preferably 1000 ° C. or lower. The heat treatment time for each stage is about 10 minutes to 1 hour. If the heat treatment time is too short, the surface modification effect may be insufficient. If the heat treatment time is too long, the productivity is lowered and the thermal influence on the magnet body may be increased. Note that if the heat treatment temperature and time at each stage in the recovery process are optimized, it can also serve as an aging treatment, and the manufacturing process can be further simplified.

  As described above, by performing the heat treatment process for recovery in two stages, as in the case of one-stage heat treatment, heat treatment in only the solid phase, only the liquid phase, or only the solid phase and the liquid phase, or 2 Even in the step heat treatment, the magnetic properties can be recovered quickly and stably compared to the temperature setting heat treatment from the liquid phase to the solid phase, and a rare earth magnet having excellent properties can be obtained. Although the details of the reason are unknown, it is considered that the interdiffusion proceeds smoothly by proceeding with the interdiffusion of elements in a solid phase to some extent and then performing diffusion having a solid-liquid interface.

  After the above-described recovery treatment step, it is preferable to apply an aging treatment to the magnet body that has been coated with a coating containing a rare earth element and whose surface has been modified. The aging step 10 is an important step in controlling the coercive force Hcj of the rare earth magnet, and for example, an aging treatment is performed in an inert gas atmosphere or in a vacuum. As the aging treatment, for example, a two-stage aging treatment is preferable. For example, in the first aging treatment step, the temperature is maintained at a temperature of about 800 ° C. for 0.1 to 3 hours. Next, it is rapidly cooled and maintained at a temperature of around 550 ° C. for 0.2 to 3 hours in the second stage aging treatment step. Since the coercive force Hcj is greatly increased by heat treatment in the vicinity of 600 ° C., when aging treatment is performed in one step, it is preferable to perform aging treatment in the vicinity of 600 ° C., for example, 450 ° C. to 650 ° C.

  As described above, in the recovery process, when the heat treatment temperature and heat treatment time of each stage are optimized so as to serve as an aging treatment, a part or all of the aging process 10 can be omitted. It is.

  Next, in the grinding step 10, the surface of the magnet body on which the coating film is formed is ground. This grinding process is performed to remove the rare earth-rich alloy remaining on the surface of the magnet body after the recovery process and the aging process, and it is only necessary to perform a simple grinding process. Of course, it is possible to omit the grinding step 10 and leave the magnet body covered with the coating.

  Finally, a corrosion-resistant film is formed by a corrosion-resistant film forming process to complete a rare earth magnet. The corrosion-resistant film may be any material as long as it functions as a protective film that prevents the magnet body from being oxidized. Examples thereof include at least one film selected from Ni, Si, Al, Cu, and Zn. it can.

  The method for forming the corrosion-resistant film is arbitrary, but when the film for surface modification is formed by the CVD method, the process can be simplified if the corrosion-resistant film is also formed by the CVD method. For example, a film containing a corrosion-resistant material is also formed by a CVD method, and a CVD film and a film containing a corrosion-resistant material are continuously formed in the same chamber for surface modification, so that the film formation process to the corrosion-resistant film formation process is performed. It can also be performed as a series of steps in the same apparatus.

  Next, specific examples of the present invention will be described based on experimental results.

<Experiment 1>
First, as a NdFeB-based sintered magnet, a rare earth sintered magnet (magnet material) made of Nd 25 wt%, Pr 2.5 wt%, Dy 2.5 wt%, Co 3 wt%, B 1 wt% and the balance Fe was prepared. This is designated as Sample 1 (Comparative Example).

  Next, the rare earth sintered magnet was cut by machining to obtain a magnet body of 10 mm × 10 mm × 0.5 mm (thickness). This is designated as Sample 2 (Comparative Example).

  Furthermore, using a device as shown in FIG. 2, these sintered magnets were placed in a 600 ° C. reactor (vacuum chamber 21), and a film was formed on the surface of the rare earth magnet while stirring. The coating was formed by the CVD method, and a β-diketone compound was used as the rare earth compound for supplying the raw material gas. The composition of the coating (CVD film) was Nd 30 atomic%, Pr 10 atomic%, Dy 50 atomic%, and the balance Fe, and the film was formed with a thickness of about 4 μm. Thereafter, these samples were subjected to a recovery heat treatment (first-stage heat treatment) at 750 ° C. for 30 minutes to perform a solid phase reaction. Next, a recovery heat treatment (second stage heat treatment) was performed at 870 ° C. for 10 minutes, and the heat treatment was performed in a state including a liquid phase. Further, an aging treatment was performed at 600 ° C. for 30 minutes. This is designated as Sample 3 (Example).

  Recovery heat treatment after film formation was performed only in one stage, and then an aging treatment was performed at 600 ° C. for 30 minutes. The recovery heat treatment was performed at 870 ° C. for 10 minutes, and the heat treatment was performed in a state including a liquid phase. This is designated as Sample 4 (Comparative Example).

  About each produced rare earth magnet, residual magnetic flux density Br, coercive force iHc, and squareness were measured. Magnet characteristics [residual magnetic flux density Br, coercive force iHc,] were measured using a BH tracer. In the BH loop, the squareness is the ratio (Hk /) of the magnetic field Hk at the point where the magnetization B is 10% lower than the residual magnetization Br and the magnetic field (coercive force iHc) at which the magnetization B becomes zero. iHc). Note that the measurement was performed on 20 samples, and the average value was obtained. The results are shown in Table 1. For samples 3 and 4, the variation range (R) when 20 samples were measured was also obtained. The results are shown in Table 2.

この表１から明らかなように、希土類元素を主体とする被膜（ＣＶＤ膜）の形成及び回復処理により、加工前の磁石素材（試料１）の磁気特性に匹敵する磁石特性を有する希土類磁石が得られることがわかる。機械加工を施した磁石素体（試料２）は、そのままでは磁気特性の劣化が大きい。また、回復熱処理の効果について試料３と試料４を比較すると、試料３は試料４と比べ、高い保磁力、角形性が得られることがわかる。試料３及び４において、バラツキのレンジ（Ｒ）を求めた結果、表２に示すように、試料４ではＲが大きく、特性にバラツキが大きいことがわかる。したがって、２段階の回復熱処理によって、安定して特性の改善が得られることがわかる。

As is apparent from Table 1, a rare earth magnet having magnet characteristics comparable to the magnetic characteristics of the magnet material (sample 1) before processing is obtained by forming and recovering a film (CVD film) mainly composed of rare earth elements. I understand that The machined magnet body (Sample 2) is greatly deteriorated in magnetic properties as it is. Further, comparing sample 3 and sample 4 with respect to the effect of the recovery heat treatment, it can be seen that sample 3 can obtain higher coercive force and squareness than sample 4. As a result of obtaining the variation range (R) for Samples 3 and 4, as shown in Table 2, it can be seen that Sample 4 has a large R and a large variation in characteristics. Therefore, it can be seen that the two-stage recovery heat treatment can stably improve the characteristics.

<Experiment 2>
In this experiment, a film was formed by PVD, and Samples 5 and 6 were prepared in the same manner as in Experiment 1. However, in Sample 5, the recovery heat treatment was a two-step heat treatment, and in Sample 6, the recovery heat treatment was a one-step heat treatment. At the time of PVD, an NdPrDyFe alloy was prepared as a target so as to have a coating composition, and sputtering was performed to coat the surface of the rare earth magnet element with the coating composition shown in Table 3. For these samples, the magnetic properties were measured in the same manner as in Experiment 1 above. The results are shown in Table 3.

  Also from Table 3, it can be seen that the two-stage heat treatment leads to stable recovery, and stable high characteristics can be obtained. Further, as a result of obtaining the variation range (R) in the same manner as in Experiment 1, it was confirmed that the variation in characteristics of Sample 5 was smaller than that of Sample 6.

<Experiment 3>
As in the previous experiment 1, first, as a NdFeB-based sintered magnet, a rare earth sintered magnet (magnet including Nd 25% by weight, Pr 2.5% by weight, Dy 2.5% by weight, Co 3% by weight, B1% by weight, and the balance Fe) Material). Next, the rare earth sintered magnet was cut by machining to obtain a magnet body of 10 mm × 10 mm × 0.5 mm (thickness).

  Furthermore, using a device as shown in FIG. 2, these sintered magnets were placed in a 600 ° C. reactor (vacuum chamber 21), and a film was formed on the surface of the rare earth magnet while stirring. The coating was formed by the CVD method, and a β-diketone compound was used as the rare earth compound for supplying the raw material gas. The composition of the coating (CVD film) was Nd 50 atomic%, Pr 20 atomic%, Dy 20 atomic%, and the balance Fe, and the film was formed with a thickness of about 4 μm. Thereafter, these samples were subjected to a recovery heat treatment (first-stage heat treatment) at 680 ° C. for 30 minutes to perform a solid phase reaction. Next, a recovery heat treatment (second stage heat treatment) was performed at 850 ° C. for 15 minutes, and the heat treatment was performed in a state including a liquid phase. Further, an aging treatment was performed at 600 ° C. for 30 minutes. This is designated as Sample 7 (Example).

  Recovery heat treatment after film formation was performed only in one stage, and then an aging treatment was performed at 600 ° C. for 30 minutes. The recovery heat treatment was performed at 850 ° C. for 15 minutes, and the heat treatment was performed in a state including a liquid phase. This is designated as Sample 8 (Comparative Example). For these samples, the magnetic properties were measured in the same manner as in Experiment 1 above. The results are shown in Table 4.

  Table 4 also shows that the two-stage heat treatment leads to stable recovery, and high characteristics can be obtained stably. Further, as a result of obtaining the variation range (R) in the same manner as in Experiment 1, it was confirmed that the variation in characteristics of Sample 7 was smaller than that of Sample 8.

<Experiment 4>
In this experiment, a film was formed by dipping, and Samples 9 and 10 were produced in the same manner as in Experiment 1 except for that. However, in Sample 9, the recovery heat treatment was a two-step heat treatment, and in Sample 10, the recovery heat treatment was a one-step heat treatment. In dipping, the molten alloy shown in Table 4 was used, and dipping was performed at 850 ° C. for 1 minute. Thereafter, these samples were subjected to recovery heat treatment (first-stage heat treatment) at 670 ° C. for 30 minutes, and then subjected to recovery heat treatment (second-stage heat treatment) at 830 ° C. for 15 minutes. Further, an aging treatment was performed at 600 ° C. for 30 minutes. Sample 10 was aged at 830 ° C. for 15 minutes and then at 600 ° C. for 30 minutes. For these samples, the magnetic properties were measured in the same manner as in Experiment 1 above. The results are shown in Table 5.

  Also from Table 5, it can be seen that the two-step heat treatment leads to stable recovery, and high characteristics can be obtained stably. Further, as a result of obtaining the variation range (R) in the same manner as in Experiment 1, it was confirmed that the variation in characteristics of the sample 9 was smaller than that of the sample 10.

It is a flowchart which shows an example of the manufacturing process of a rare earth magnet. It is a schematic diagram which shows an example of a CVD apparatus. It is a phase diagram of DyFe system alloy. It is a phase diagram of a NdFe-type alloy.

Explanation of symbols

1 alloying process, 2 coarse grinding process, 3 fine grinding process, 4 magnetic field forming process, 5 sintering process, 6 machining process, 7 CVD process, 8 recovery process, 9 aging process, 10 grinding process, 11 Corrosion-resistant film forming process, 21 vacuum chamber, 22 vacuum exhaust mechanism, 23 raw material gas supply means, 24 carrier gas source, 25 rare earth compound, 26 raw material container, 27 shower head, 28 magnet body, 29 flow meter, 30 adjustment valve

Claims (9)

After forming a film mainly composed of rare earth elements on the surface of the magnet body, two-stage heat treatment is performed,
Heat treatment at a temperature of 500 ° C. or higher and lower than the melting point of the coating in the first stage , heat treatment at a temperature of melting point of the coating and 1000 ° C. or lower in the second stage
And the manufacturing method of the rare earth magnet characterized by making heat processing time of each step into 10 minutes-1 hour.   2. A rare earth sintered magnet is produced by sintering a compact formed from a raw material alloy fine powder containing a rare earth element, a transition metal element and boron, and the rare earth sintered magnet is used as a magnet body. The manufacturing method of the rare earth magnet of description.   3. The method for producing a rare earth magnet according to claim 2, wherein an NdFeB-based rare earth sintered magnet is used as the magnet body.   4. The method for producing a rare earth magnet according to claim 1, wherein the film is formed after the magnet body is machined to a predetermined thickness. 5. The method for producing a rare earth magnet according to claim 4, wherein the thickness of the magnet body is 2 mm or less (however, 0 mm is not included) .   6. The method for producing a rare earth magnet according to claim 1, wherein the coating contains at least one selected from Nd, Pr, Dy, and Tb. The method for producing a rare earth magnet according to claim 6, wherein the coating has a melting point of 1000 ° C. or less .   The method of manufacturing a rare earth magnet according to claim 1, wherein the film is formed by any one of a physical vapor deposition method, a chemical vapor deposition method, and a dipping method.   The method for producing a rare earth magnet according to any one of claims 1 to 8, wherein an aging treatment is performed at a temperature of 450 ° C to 650 ° C after the two-stage heat treatment.

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