JP2012151286A - Method of producing r-t-b-based sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffusion treatment of a heavy rare-earth element RH exhibiting excellent mass productivity.SOLUTION: A method of producing an R-T-B-based sintered magnet includes a step for preparing an R-T-B-based sintered magnet body, a step for preparing an RH diffusion source consisting of an R-T-B-based alloy where the content of a heavy rare-earth element RH (at least any one kind of Dy, Tb) is higher by at least 0.5 mass% than the content of the R-T-B-based sintered magnet body, a step for charging the R-T-B-based sintered magnet body and the RH diffusion source into a processing container so that they can move relatively and can approach or come into contact with each other, and an RH diffusion step for performing heat treatment at 800-1000°C while moving the R-T-B-based sintered magnet body and the RH diffusion source continuously or intermittently in a processing chamber.

Description

The present invention relates to a method for producing an R-T-B system sintered magnet (R is a rare earth element, T is a transition metal element containing Fe) having an R ₂ T ₁₄ B type compound as a main phase.

R-T-B based sintered magnets having R ₂ T ₁₄ B-type compound as the main phase are known as the most powerful magnets among permanent magnets, and include voice coil motors (VCMs) for hard disk drives, It is used for various motors such as motors for hybrid vehicles and home appliances.

  The RTB-based sintered magnet has irreversible thermal demagnetization because the coercive force decreases at high temperatures. In order to avoid irreversible thermal demagnetization, when used for a motor or the like, it is required to maintain a high coercive force even at a high temperature.

The R-T-B based sintered magnet is known to improve the coercive force when a part of R in the R ₂ T ₁₄ B type compound phase is replaced with a heavy rare earth element RH (Dy, Tb). . In order to obtain a high coercive force at a high temperature, it is effective to add a large amount of heavy rare earth element RH to the RTB-based sintered magnet.

  However, in the R-T-B based sintered magnet, if the light rare earth element RL (Nd, Pr) is replaced with R with the heavy rare earth element RH, the coercive force is improved while the residual magnetic flux density is lowered. There is. Further, since the heavy rare earth element RH is a rare resource, it is required to reduce the amount of use thereof.

  Therefore, in recent years, it has been studied to improve the coercive force of the sintered magnet with less heavy rare earth element RH so as not to reduce the residual magnetic flux density. The applicant of the present application has already arranged an RTB-based rare earth sintered magnet body and a bulk body containing heavy rare earth element RH in the processing chamber in Patent Document 1, and set the processing chamber to 700 ° C. or more and 1000 ° C. or less. While heating, the rare earth element RH such as Dy is supplied to the surface of the RTB-based sintered magnet body, and the heavy rare earth element RH is diffused from the surface into the sintered magnet body ("deposition diffusion"). ) Discloses the method. In Patent Document 1, an RTB-based sintered magnet body and an RH bulk body are arranged to face each other with a predetermined interval inside a processing chamber made of a refractory metal material. The processing chamber includes a member that holds a plurality of sintered magnet bodies and a member that holds an RH bulk body. As these holding members, a configuration is disclosed that includes a spacer portion that sets a distance between the sintered magnet body and the RH bulk body, and a net portion on which the sintered magnet body or the RH bulk body is placed. In the method using such an apparatus, the step of disposing the RH bulk body in the processing chamber, the step of disposing the sintered magnet body via the holding member above the RH bulk body, and the RH via the holding member above the RH bulk body. After completing a series of multi-stage arrangement steps, which are the steps of arranging the bulk body, vapor deposition diffusion is performed under the above temperature conditions.

  Patent Document 2 discloses that an oxide, fluoride, and oxyfluoride powder of heavy rare earth element RH is present on the surface of an RTB-based sintered magnet body, and the temperature is equal to or lower than the sintering temperature of the sintered magnet body. It discloses a method for improving the coercive force of a sintered magnet by diffusing heavy rare earth elements RH from the surface of the sintered magnet body by applying a heat treatment in a vacuum or an inert gas.

International Publication WO 2007/102391 International Publication WO 2006/043348

  In the method of Patent Document 1, since the heavy rare earth element RH can be supplied and diffused to the sintered magnet body at a relatively low temperature of 700 ° C. or higher and 1000 ° C. or lower, the weight on the RTB-based sintered magnet body is increased. The supply amount of rare earth element RH was not excessive, and an RTB-based sintered magnet with improved coercive force with almost no decrease in residual magnetic flux density could be produced.

  However, in order to supply and diffuse an appropriate amount of the heavy rare earth element RH, it is necessary to arrange the RTB-based sintered magnet body and the RH diffusion source at a predetermined interval so as to be troublesome. There is a problem that it is inferior in mass production.

  In addition, since the heavy rare earth element RH is supplied to the RTB-based sintered magnet body by vaporization and sublimation, the heavy rare earth element RH can be efficiently diffused into the RTB-based sintered magnet body. Is preferably heated at a relatively high temperature, but if the temperature is increased, the supply of heavy rare earth element RH becomes excessive, and the heavy rare earth element RH between the surface layer portion and the inside of the RTB-based sintered magnet body In the main phase crystal grains in the vicinity of the surface layer, the heavy rare earth element RH diffuses deeply, and there is a possibility that the residual magnetic flux density is lowered. Further, welding may occur between the RH diffusion source and the RTB-based sintered magnet body and between the holding member and the RTB-based sintered magnet body during the diffusion process.

  In addition, a part of the heavy rare earth element RH vaporized and sublimated from the RH diffusion source is scattered to the holding member, the inner wall of the processing chamber, and the vacuum evacuation device, but these heavy rare earth elements RH are effectively utilized. It becomes useless.

  In the method of Patent Document 2, since only the amount of heavy rare earth element RH applied to the surface of the RTB-based sintered magnet body diffuses into the RTB-based sintered magnet body, a stable coercive force is achieved. In order to obtain the improvement effect, it is necessary to strictly control the coating amount and the thickness of the coating layer, and such a coating operation becomes very complicated. Moreover, since the heavy rare earth element RH has been attached to the surface of the RTB-based sintered magnet body from the beginning of the diffusion treatment, the concentration gradient of the heavy rare earth element RH is large, and the RTB-based sintered magnet In the outermost layer portion of the body, RH diffusion is diffused deep into the main phase crystal grains, and the residual magnetic flux density is likely to decrease. Furthermore, since oxides, fluorides, and oxyfluorides of heavy rare earth elements RH are used as the RH diffusion source, oxygen and fluorine remain inside the magnet after the diffusion treatment, and there is a limit to improving the magnet characteristics. .

  The present invention has been made in view of the above circumstances, and the object thereof is to reduce the heavy rare earth elements RH such as Dy and Tb from the surface of the R-T-B system sintered magnet body without reducing the residual magnetic flux density. In the manufacturing method of the R-T-B system sintered magnet to be diffused into the surface, it is to provide a manufacturing method capable of mass-producing the R-T-B system sintered magnet having a high coercive force by a relatively simple method. .

The method for producing an RTB-based sintered magnet of the present invention includes a step of preparing an RTB-based sintered magnet body,
RH made of an RTB-based alloy in which the content of heavy rare earth element RH (at least one of Dy and Tb) is at least 0.5 mass% higher than the content of the RTB-based sintered magnet body Preparing a diffusion source;
Charging the RTB-based sintered magnet body and the RH diffusion source into a processing container so as to be relatively movable and close to or in contact with each other;
An RH diffusion step of performing heat treatment at 800 ° C. or more and 1000 ° C. or less while continuously or intermittently moving the RTB-based sintered magnet body and the RH diffusion source in the processing chamber. is doing.

  In a preferred embodiment, in the step of preparing the RH diffusion source, the RH diffusion source is polished, cut or crushed.

  In a preferred embodiment, a stirring auxiliary member is further charged into the processing chamber before or during the RH diffusion.

  According to the present invention, not only is the work of charging the RTB-based sintered magnet body and the RH diffusion source into the processing chamber easy, but they are moved continuously and intermittently in the processing chamber. However, since RH diffusion is performed at a predetermined temperature, welding between the sintered magnet body and the RH diffusion source during the diffusion process can be prevented, and an RTB-based sintered magnet having a high coercive force can be obtained with high productivity. . In particular, by using an RTB-based alloy having a composition ratio similar to that of the RTB-based sintered magnet body as the RH diffusion source, the RTB-based sintered magnet body is used during the RH diffusion treatment. The heavy rare earth element RH can be diffused into the R-T-B system sintered magnet body without excessively increasing the liquid phase amount, and a decrease in the residual magnetic flux density of the sintered magnet can be suppressed.

It is sectional drawing which shows typically the structure of the diffusion apparatus used by preferable embodiment of this invention. It is a graph which shows an example of the heat pattern at the time of a diffusion process process.

One embodiment of the method for producing the RTB-based sintered magnet of the present invention will be described below.
Here, the sintered magnet (material) before completion of the RH diffusion process is referred to as “R-T-B system sintered magnet body”, and the sintered magnet (diffusion magnet) after completion of the RH diffusion process is referred to as “R-T-B system”. This is distinguished from “sintered magnet”.

  In the RH diffusion step, for example, by rotating or swinging the processing container or applying vibration to the processing container, the RTB-based sintered magnet body and the RH diffusion source are placed in the processing container. It moves continuously or intermittently to change the position of the contact portion between the RTB-based sintered magnet body and the RH diffusion source, or the RTB-based sintered magnet body and the RH diffusion source. Are supplied in direct contact with heavy rare earth element RH and / or supply by vaporization / sublimation and diffusion to an RTB-based sintered magnet body (RH diffusion step). .

  In the above RH diffusion treatment process, the grain boundary phase (R-rich phase) and the outermost surface of the main phase crystal of the R-T-B system sintered magnet body are dissolved to form a liquid phase. By supplying RH, the rare earth component contained in the liquid phase is changed to rich in the heavy rare earth element RH, and in the resolidification process, the heavy rare earth element RH is concentrated by being distributed more on the main phase side. A main phase outer shell is formed.

  However, when only a large amount of heavy rare earth element RH is supplied, the liquid phase component during RH diffusion treatment changes greatly, so that the surface of the main phase melts out (increase in the main phase elution amount as the liquid phase amount increases). It is estimated that the concentration of heavy rare earth element RH in the outer shell of the main phase becomes thicker during re-solidification and the magnetization of the main phase crystal decreases (the residual magnetic flux density decreases as a magnet) Is done.

  Further, if the main phase surface layer portion is melted out a lot, RH diffusion occurs between the RH diffusion source and the RTB-based sintered magnet body, and between the holding member and the RTB-based sintered magnet body. There is concern about the occurrence of welding during the process.

  In the present invention, by using an RTB-based alloy having a composition ratio similar to that of the RTB-based sintered magnet body as the RH diffusion source, the RTB-based sintering is performed during the RH diffusion process. R, T, B composition of the liquid phase component generated from the liquid phase component before starting the diffusion process of the magnet body and the RH diffusion source is approximated (however, the amount of heavy rare earth element RH in R As a result, the heavy rare earth element RH can be diffused into the RTB-based sintered magnet without excessively increasing the liquid phase amount of the RTB-based sintered magnet body.

  Further, since an excessive liquid phase is not generated during the RH diffusion step, a predetermined amount of the heavy rare earth element RH can be converted to R-T not only by vaporization / sublimation of the heavy rare earth element RH but also by direct contact without causing welding. Since it can supply to -B type sintered compact, the feature of the manufacturing method of the present invention can be expressed more effectively.

  Further, unlike the methods of Patent Document 1 and Patent Document 2, the concentration of the rare earth element R in the liquid phase does not change greatly, so that the liquid phase is transferred from the RH diffusion source or the R-T-B system sintered body to the outside. Exudation is suppressed and welding with the processing member can be prevented.

  In addition, the RH diffusion source and the R-T-B system sintered magnet body are loaded into the processing vessel so as to be relatively movable and close to or in contact with each other, and are moved continuously or intermittently to thereby move the RH diffusion source. And the RTB-based sintered body are not maintained in a specific contact state, and the contact state can be changed at any time (movement of the contact point), in combination with the effect of the composition of the RH diffusion source, These welding prevention effects can be further enhanced.

  In addition, the RH diffusion source and the R-T-B system sintered magnet body are loaded into the processing container so as to be relatively movable and close to or in contact with each other, and are moved continuously or intermittently. Since RH diffusion can be achieved, a process of disposing the R-T-B system sintered magnet body and the RH diffusion source at a predetermined position is unnecessary compared with the method of Patent Document 1, and compared with the method of Patent Document 2. , Complicated operations such as application of an RH diffusion source become unnecessary.

  In the present invention, the diffusion step for RH diffusion is performed in a temperature range of 800 ° C. or higher and 1000 ° C. or lower. The temperature range of 800 ° C. or more and 1000 ° C. or less is a temperature range in which RH diffusion is promoted in the RTB-based sintered magnet body, and the heavy rare earth element RH is placed inside the RTB-based sintered magnet body. RH diffusion can be performed in a situation where diffusion is easy.

  That is, if the temperature is lower than 800 ° C., the desired supply / diffusion of RH cannot be realized, and if it exceeds 1000 ° C., the supply of heavy rare earth element RH to the RTB-based sintered magnet body becomes excessive, and the residual magnetic flux density decreases. Is concerned.

  Here, in the RH diffusion step, as a method of moving the RTB-based sintered magnet body and the RH diffusion source continuously or intermittently in the processing vessel, the RTB-based sintered magnet body is used. Any method can be adopted as long as the mutual arrangement relationship between the RH diffusion source and the RTB-based sintered magnet body can be changed without causing chipping or cracking. For example, a method of rotating or swinging the processing container or applying vibration to the processing container from the outside can be adopted. Moreover, you may provide a stirring means in a processing container.

[RTB-based sintered magnet body]
First, in the present invention, an RTB-based sintered magnet body to be diffused of heavy rare earth element RH is prepared. The RTB-based sintered magnet body has the following composition, for example.
R (rare earth element): 28 mass% or more and 33 mass% or less B (part of B may be substituted with C): 0.80 mass% or more and 1.2 mass% or less T (mainly Fe Transition metal, which may contain Co) and inevitable impurities: the balance,
Further, a part of T may be replaced with the additive element M within the following range.
Additive element M (selected from the group consisting of Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi At least one): 0 to 0.5% by mass

  Here, the rare earth element R is at least one element selected from light rare earth elements such as Nd and Pr, but may contain a heavy rare earth element. When a heavy rare earth element is contained, it is preferable to include at least one of Dy and Tb.

  The RTB-based sintered magnet body having the above composition is manufactured by a known manufacturing method.

[RH diffusion source]
The RH diffusion source is an RTB-based alloy in which the content of heavy rare earth elements RH (at least one of Dy and Tb) is at least 0.5 mass% higher than the content of the RTB-based sintered magnet body Consists of.
This RTB-based alloy satisfies the conditions for the content of the rare earth element RH and has, for example, the following composition.
R (rare earth element including heavy rare earth element RH): 28.0 mass% or more and 40 mass% or less B (part of B may be substituted with C): 0.1 mass% or more and 1.5 mass% Hereinafter, T (which is a transition metal mainly containing Fe and may contain Co) and inevitable impurities: the remainder T may be partially replaced with the additional element M in the following range.
Additive element M (selected from the group consisting of Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi At least one): 0 to 0.5% by mass

  If the amount of the heavy rare earth element RH contained in the RH diffusion source is 0.5 mass% or more than the heavy rare earth element RH contained in the RTB-based sintered magnet body before the RH diffusion step, the present invention. The effect is obtained. When the amount of the RH diffusion source is 0.5 mass%, the diffusion of the heavy rare earth element RH from the RH diffusion source to the RTB-based sintered magnet body can be performed smoothly.

  When the difference in the heavy rare earth element RH between the RTB-based sintered magnet body and the RH diffusion source is less than 0.5% by mass, the diffusion of the RH element does not proceed sufficiently and the target coercive force is improved. The effect is not obtained.

  In order to approximate the composition of the liquid phase during the diffusion process to the RTB-based sintered magnet body that is the base material, the amount of B contained in the RH diffusion source is 0.1 mass% or more and 1.5 mass% or less. To. The amount of B is preferably 0.5% by mass or more and 1.2% by mass or less.

The R-T-B type alloy used for the RH diffusion source only needs to satisfy at least the content condition of the heavy rare earth element RH. For example, R-T-B having a main phase composed of an R ₂ T ₁₄ B compound. It is possible to use sintered magnet scraps that are cracked or chipped during the manufacturing process of the sintered magnet, that are out of dimensional standards, or sintered magnet scraps that remain after processing into a predetermined shape.

  In addition, an RTB-based alloy cast (hereinafter referred to as raw material scrap) generated during the manufacturing process of an RTB-based sintered magnet body that satisfies the same conditions may be used. A prepared R-T-B alloy may be used.

  Furthermore, a mixture of the sintered magnet scrap, the raw alloy scrap, and the alloy, or a predetermined amount of heavy rare earth elements RH and RH compounds may be mixed and used.

  In particular, when the sintered magnet scrap is an RH diffusion source, the RH diffusion source is used when performing the RH diffusion process while continuously or intermittently moving the RTB-based sintered magnet body and the sintered magnet scrap. However, since it is uniformly mixed and stirred without being separated from the RTB-based sintered magnet body during processing, there is an effect of realizing better RH diffusion.

  The form of the RH diffusion source when charging the processing container is arbitrary, for example, spherical, linear, plate-like, block-like. The shape of the RH diffusion source is not particularly limited.

  Moreover, it is preferable to use the thing of the RH diffusion source at the time of charging in a processing container which passed the sieve with 2 mm of openings. By setting the size of the RH diffusion source to 2 mm or less, RH diffusion from the RH diffusion source to the RTB-based sintered magnet body is promoted.

  In the step of preparing the RH diffusion source, it is preferable to remove the oxide film on the surface of the RH diffusion source. By removing the oxide film, the supply and diffusion of the heavy rare earth element RH from the RH diffusion source to the RTB-based sintered magnet body can be more effectively realized. The RH diffusion source is preferably crushed to remove the oxide film.

The RH diffusion source may be used after being polished, cut or crushed.
Here, the polishing means, for example, polishing the surface of the RH diffusion source by shot blasting, or putting it in a barrel to polish the surface of the RH diffusion source and exposing the clean surface of the RH diffusion source. Cutting is, for example, cutting the RH diffusion source with a diamond cutter to expose the clean surface of the RH diffusion source. Crushing is, for example, crushing the RH diffusion source with a hammer to expose the clean surface of the RH diffusion source.

[Agitation auxiliary member]
In the embodiment of the present invention, it is preferable to introduce a stirring auxiliary member into the processing vessel in addition to the RTB-based sintered magnet body and the RH diffusion source. The stirring auxiliary member promotes contact between the RTB-based sintered magnet body and the RH diffusion source, and the heavy rare earth element RH once adhered to the stirring auxiliary member is indirectly transferred to the RTB-based sintered magnet body. The role to supply. Furthermore, the stirring assisting member also has a role of preventing chipping due to contact between the RTB-based sintered magnet body and the RH diffusion source in the processing container.

  The agitation auxiliary member is shaped so as to easily move in the processing vessel, and the agitation auxiliary member is mixed with the R-T-B system sintered magnet body and the RH diffusion source to at least one of rotation, oscillation or vibration of the processing vessel. It is effective to do. Examples of shapes that are easy to move here include spherical shapes, elliptical shapes, and cylindrical shapes having a diameter of several hundred μm to several tens of mm.

  The stirring assisting member is preferably formed from a material that does not easily react with the RTB-based sintered magnet body during the RH diffusion treatment. The stirring auxiliary member can be suitably formed from ceramics of zirconia, silicon nitride, silicon carbide and boron nitride, or a mixture thereof. The ceramics of zirconia, silicon nitride, silicon carbide and boron nitride, or a mixture thereof have a specific gravity almost equal to that of the R-T-B type sintered magnet body, so that stirring is easy.

  Moreover, as a metal material which does not easily react with the RTB-based sintered magnet body, Mo, W, Nb, Ta, Hf, Zr, or a metal, an alloy containing at least one of these, or a mixture thereof is used. Can also be formed.

[RH diffusion process]
A preferred example of the diffusion treatment process according to the present invention will be described with reference to FIG.
In the example shown in FIG. 1, an RTB-based sintered magnet body 1 and an RH diffusion source 2 are introduced into a stainless steel cylinder 3. Here, it is preferable that the R—T—B-based alloy serving as the RH diffusion source 2 is crushed, cut, or polished before being charged into the processing vessel.

  Although not shown, it is preferable that a zirconia sphere or the like is introduced into the cylinder 3 as a stirring auxiliary member. In this example, the cylinder 3 functions as a “processing container (processing chamber)”. The material of the cylinder 3 is not limited to stainless steel, and may be any material as long as it has heat resistance that can withstand temperatures exceeding 1000 ° C. and is difficult to react with the RTB-based sintered magnet body 1 and the RH diffusion source 2. It is. For example, Nb, Mo, W, or an alloy containing at least one of them may be used. An Fe—Cr—Al alloy or an Fe—Cr—Co alloy obtained by adding Al or Co to austenitic stainless steel may be used. The tube 3 is provided with a lid 5 that can be opened and closed or removed. Further, on the inner wall of the tube 3, a protrusion is installed so that the RH diffusion source 2 and the RTB-based sintered magnet body 1 can move in proximity or contact with each other while moving continuously or intermittently. Can do. The cross-sectional shape perpendicular to the major axis direction of the cylinder 3 is not limited to a circle, and may be an ellipse, a polygon, or other shapes. The cylinder 3 in the state shown in FIG. 1 is connected to an exhaust device 6. The inside of the cylinder 3 can be depressurized by the action of the exhaust device 6. An inert gas such as Ar can be introduced into the cylinder 3 from a gas cylinder (not shown).

  The cylinder 3 is heated by a heater 4 disposed on the outer periphery thereof. The cylinder 3 is supported so as to be rotatable about its central axis by heating, and can be rotated by the variable motor 7 during heating by the heater 4. The rotational speed of the cylinder 3 can be set, for example, to a peripheral speed of the inner wall surface of the cylinder 3 of 0.005 m or more per second. It is preferably set to 0.5 m or less per second so that the RTB-based sintered magnet body in the cylinder and the RH diffusion source collide with each other due to rotation.

  In the example of FIG. 1, the cylinder 3 rotates, but the present invention is not limited to such a case. It suffices that the RTB-based sintered magnet body 1 and the RH diffusion source 2 are relatively movable and contactable in the cylinder 3 during the RH diffusion process. For example, the cylinder 3 may swing or vibrate without rotating, or at least two of rotation, swing and vibration may occur simultaneously.

Next, for example, a procedure of RH diffusion processing performed using the processing apparatus of FIG. 1 will be described.
First, the lid 5 is removed from the cylinder 3 and the inside of the cylinder 3 is opened. After the plurality of RTB-based sintered magnet bodies 1 and the RH diffusion source 2 are inserted into the cylinder 3, the lid 5 is attached to the cylinder 3 again. The exhaust device 6 is connected and the inside of the cylinder 3 is evacuated. After the internal pressure of the cylinder 3 is sufficiently reduced, the exhaust device 6 is removed. Inert gas is introduced to the required pressure, and heating by the heater 4 is performed while rotating the cylinder 3 by the motor 7.

The inside of the tube 3 during the RH diffusion treatment is preferably an inert atmosphere. The “inert atmosphere” in this specification includes a vacuum or an inert gas. In addition, the “inert gas” is a rare gas such as argon (Ar), for example, but may be a gas that does not chemically react between the RTB-based sintered magnet body 1 and the RH diffusion source 2. For example, it can be included in an “inert gas”. It is preferable that the pressure of an inert gas is below atmospheric pressure. In the present embodiment, since the RTB-based sintered magnet body 1 and the RH diffusion source 2 are close to or in contact with each other, RH diffusion can be performed without increasing the degree of vacuum. In addition, the correlation between the degree of vacuum and the supply amount of RH is relatively small, and even if the degree of vacuum is further increased, the supply amount of heavy rare earth element RH (degree of improvement in coercive force) is not greatly affected. The atmospheric pressure is 10 ⁻³ Pa to atmospheric pressure. The supply amount is more sensitive to the temperature of the RTB-based sintered magnet body 1 than the atmospheric pressure.

  In the present embodiment, the R—T—B-based sintered magnet body 1 and the RH diffusion source 2 containing more heavy heavy rare earth element RH are rotated and heated together, thereby heating the heavy rare earth element RH from the RH diffusion source 2. While being supplied to the surface of the RTB-based sintered magnet body 1, it can be diffused inside.

  The peripheral speed of the inner wall surface of the processing chamber during the diffusion process can be set to 0.005 m / s or more, for example. When the rotation speed is lowered, the movement of the contact portion between the RTB-based sintered magnet body 1 and the RH diffusion source 2 becomes slow, and welding is likely to occur. It is preferable to select a preferable rotation speed as appropriate depending on the diffusion temperature, the shape and size of the RH diffusion source, the amounts of the RTB-based sintered magnet body 1 and the RH diffusion source 2, and the like.

  In the present embodiment, the temperature of the RTB-based sintered magnet body 1 and the RH diffusion source 2 is maintained within a range of 800 ° C. or higher and 1000 ° C. or lower. This temperature range is a preferable temperature range in which the heavy rare earth element RH diffuses inward through the grain boundary phase of the RTB-based sintered magnet body 1. More preferably, it is a temperature region in which the diffusion temperature exceeds 850 ° C. If it exceeds 850 ° C., the heavy rare earth element RH can be diffused more efficiently inside. The time of heat processing is 10 minutes or more and 72 hours or less, for example. Preferably it is 1 hour or more and 12 hours or less.

  When the processing temperature exceeds 1000 ° C., the supply of heavy rare earth element RH to the R-T-B system sintered magnet body becomes excessive, and there is a concern that the residual magnetic flux density may be lowered. The problem that the sintered magnet body 1 and the RH diffusion source 2 are welded easily occurs, and the RTB-based sintered magnet body itself may be melted or the structure may be changed. . On the other hand, if the processing temperature is less than 800 ° C., the desired supply / diffusion of RH cannot be realized.

  The holding time is the ratio of the charged amounts of the RTB-based sintered magnet body 1 and the RH diffusion source 2 when performing the RH diffusion treatment step, the RTB-based sintered magnet body 1 and the RH diffusion source. 2 and the amount of heavy rare earth element RH (diffusion amount) to be diffused into the RTB-based sintered magnet body 1 by the RH diffusion treatment are preferably determined.

The pressure of the atmospheric gas during the RH diffusion step (atmospheric pressure in the processing chamber) can be set in the range of 10 ⁻³ Pa to atmospheric pressure.

  After the RH diffusion step, a first heat treatment may be performed on the RTB-based magnet body 1 for the purpose of homogenizing the diffused heavy rare earth element RH. After removing the RH diffusion source 2, the heat treatment is performed in the range of 700 ° C. or higher and 1000 ° C. or lower where the heavy rare earth element RH can substantially diffuse, more preferably 800 ° C. or higher and 950 ° C. or lower. Since this first heat treatment is performed after removing the RH diffusion source 2, no further supply of the heavy rare earth element RH to the inside of the RTB-based sintered magnet body 1 occurs, but RT- Since diffusion of the heavy rare earth element RH occurs in the B-based sintered magnet body 1, the heavy rare earth element RH is diffused deeply from the surface side of the RTB-based sintered magnet, and the RTB-based sintered magnet is obtained. As a whole, the coercive force can be increased. The time for the first heat treatment is, for example, not less than 10 minutes and not more than 72 hours. Preferably it is 1 hour or more and 12 hours or less. Here, the atmospheric pressure of the heat treatment furnace for performing the first heat treatment is equal to or lower than the atmospheric pressure. Preferred is 10 kPa or less.

  The RH diffusion step and the first heat treatment may be performed with separate heat treatment apparatuses, or may be performed continuously with one heat treatment apparatus.

[Second heat treatment]
Moreover, you may perform 2nd heat processing (400 degreeC or more and 700 degrees C or less) for the purpose of raising a coercive force as needed. When both the first heat treatment (700 ° C. and 1000 ° C.) and the second heat treatment are performed, the second heat treatment is preferably performed after the first heat treatment. The first heat treatment (700 to 1000 ° C.) and the second heat treatment (400 to 700 ° C.) may be performed in the same processing chamber. The time for the second heat treatment is, for example, not less than 10 minutes and not more than 72 hours. Preferably it is 1 hour or more and 12 hours or less. Here, the atmospheric pressure of the heat treatment furnace for performing the second heat treatment is equal to or lower than the atmospheric pressure. Preferred is 10 kPa or less. Note that only the second heat treatment may be performed without performing the first heat treatment.

[Experimental Example 1]
First, R- with a composition ratio Nd = 28.5, Dy = 2.0, B = 1.0, Co = 0.9, Al = 0.1, Cu = 0.1, and the balance = Fe (mass%). A TB sintered magnet body was produced. By machining this, a 7.4 mm × 7.4 mm × 7.4 mm cubic RTB-based sintered magnet body was obtained. When the magnetic properties of the _RTB -based sintered magnet body produced for comparison were measured with a BH tracer, the coercive force _HcJ was 1250 kA / m and the residual magnetic flux density B was the property after heat treatment (500 ° C.). _r was 1.38T.

Next, RH diffusion processing was performed using the apparatus of FIG. The volume of the cylinder was 128000 mm ³ , the weight of the R-T-B system sintered magnet body (or the number of charged elements): 50 g (5), and the weight of the RH diffusion source: 50 g. As the RH diffusion source, various RTB-based alloys having different amounts of Nd, Pr, Dy, and Tb shown in Table 1 were crushed and used. The size was 2 mm or less with a sieve opening.

  The temperature in the processing container during the diffusion treatment changed as shown in FIG. FIG. 2 is a graph showing the temperature change (heat pattern) in the processing container after the start of heating. In the example of FIG. 2, evacuation was performed while the temperature was raised by the heater. The temperature rising rate is about 10 ° C./min. The temperature was maintained at about 600 ° C. until the pressure in the processing vessel reached 10 Pa. Thereafter, rotation of the processing container was started, and the temperature was increased until the diffusion processing temperature was reached. The temperature rising rate was about 10 ° C./min. After reaching the RH diffusion temperature in Table 1, the temperature was maintained at that temperature for the RH diffusion time in Table 1. Thereafter, heating by the heater was stopped and the temperature was lowered to about room temperature. Thereafter, the R-T-B sintered magnet after completion of the RH diffusion process taken out from the apparatus of FIG. 1 is put into another heat treatment furnace, and the first heat treatment (900 ° C., 4 hours) at the same atmospheric pressure as that during the diffusion treatment. And second heat treatment (500 ° C., 4 hours).

When RH diffusion processing was performed using RH diffusion sources (samples 1 to 12) with different Dy amounts and Tb amounts, the results shown in Table 1 were obtained. Here, the magnetic characteristics are as follows. Each surface of the RTB system magnet after the diffusion treatment is ground by 0.2 mm and processed into a 7.0 mm × 7.0 mm × 7.0 mm cube, and then the BH tracer. The magnet characteristics are evaluated. In the table, the “RH diffusion source” column shows the composition of the RH diffusion source used in the diffusion treatment process. In the “peripheral speed” column, the peripheral speed of the inner wall surface of the cylinder 3 shown in FIG. 1 is shown. In the “RH diffusion temperature” column, the temperature in the cylinder 3 held during the diffusion process is shown. The column “RH diffusion time” indicates the time during which the RH diffusion temperature is maintained. “Atmospheric pressure” indicates the pressure at the start of the diffusion treatment. The amount of increase in coercive force H _cJ after completion of the RH diffusion step is _indicated by “ΔH _cJ ”, and the amount of increase in residual magnetic flux density B _r after completion of the RH diffusion step is indicated by “ΔB _r ”.

  As can be seen from Table 1, within the scope of the present invention, the decrease in residual magnetic flux density was suppressed and the coercive force was improved. Further, no welding occurred.

_Within the scope of the present invention, samples 1 to 4 subjected to the RH diffusion treatment under the same conditions except for the composition of the RH diffusion source have the highest coercive force improving effect (ΔH _cJ ) in sample 1 from Table 1 and the residual. It was found that there was no decrease in magnetic flux density. It was found that the coercive force improving effect (ΔH _cJ ) is increased corresponding to the Dy content of the RH diffusion source. Further, in Sample 5, since the RTB-based sintered magnet body 2 has a lower Dy content than the RTB-based sintered magnet body, the Dy diffusion does not proceed and the coercive force improving effect (ΔH _cJ ) is obtained. There wasn't.

Sample 6 that was subjected to RH diffusion treatment under the same conditions except for the composition of the RH diffusion source had a coercive force improving effect (ΔH _cJ ) of 200 kA / m from Table 1 and there was no decrease in residual magnetic flux density. all right.

From Samples 7 and 8, RH diffusion sources with different amounts of B in the composition of the RH diffusion source also had a coercive force improving effect (ΔH _cJ ) and no decrease in residual magnetic flux density.

From Sample 9, even a composition further containing Pr had a coercive force improving effect (ΔH _cJ ) and no decrease in residual magnetic flux density.

Further, from Samples 10 and 11, in the present invention, even if the atmospheric pressure was high, there was an effect of improving the coercive force (ΔH _cJ ), and there was no decrease in the residual magnetic flux density.

  From Sample 12, it was found that when RH diffusion was performed at 700 ° C., the desired effect of improving the coercive force could not be obtained.

[Experiment 2]
Here, RH diffusion treatment was performed under the same conditions as in Experimental Example 1 except that a zirconia sphere having a diameter of 5 mm was added as a stirring auxiliary member with a weight of 50 g, and RH diffusion treatment and first heat treatment were performed, and magnetic characteristics were evaluated. However, the results shown in Table 2 were obtained.
As shown in Table 2, Samples 13 to 21 have an effect of improving _{HcJ in} a short time despite the fact that the RH diffusion treatment time was halved compared to Samples 1 to 4, 6 to 8, 10, and 11. And _Br is hardly lowered. From the results of Samples 15, 20, and 21, it was found that even if the atmospheric pressure is high, there is an effect of increasing the coercive force without reducing the residual magnetic flux density.
It was confirmed that the occurrence of chipping was suppressed in samples 13 to 21 using the stirring auxiliary member as compared with samples 1 to 12.

[Experiment 3]
When the RH diffusion source was subjected to the RH diffusion treatment under the same conditions as Sample 8 except that the RH diffusion source was sintered scrap having the composition shown in Table 3, the results shown in Table 3 were obtained. All of Samples 22 to 25 had a coercive force improving effect (ΔH _cJ ) as in Samples 1 to 4, and there was no decrease in residual magnetic flux density. It was found that the coercive force improving effect (ΔH _cJ ) is increased corresponding to the Dy content of the RH diffusion source.

As can be seen from the above, the RH diffusion source made of the RTB-based alloy and the RTB-based sintered magnet body are moved continuously or intermittently in a processing vessel heated to a predetermined temperature. However, by bringing them close to or in contact with each other, it is possible to effectively introduce the heavy rare earth element RH of the RH diffusion source into the grain boundary of the RTB-based sintered magnet body with good mass productivity and improve the magnet characteristics. It has become possible.
The heat pattern that can be executed by the diffusion processing of the present invention is not limited to the example shown in FIG.

  According to the present invention, an RTB-based alloy can be used as an RH diffusion source, and the RTB-based sintered magnet body can be subjected to RH diffusion treatment.

1 R-T-B system sintered magnet body 2 RH diffusion source 3 cylinder 4 heater 5 lid 6 exhaust device

Claims (3)

Preparing an RTB-based sintered magnet body;
It is made of an RTB-based alloy in which the content of heavy rare earth element RH (at least one of Dy and Tb) is at least 0.5 mass% higher than the content of the RTB-based sintered magnet body. Preparing an RH diffusion source;
Charging the RTB-based sintered magnet body and the RH diffusion source into a processing container so as to be relatively movable and close to or in contact with each other;
An RH diffusion step of performing a heat treatment at 800 ° C. or higher and 1000 ° C. or lower while continuously or intermittently moving the RTB-based sintered magnet body and the RH diffusion source in the processing chamber;
For producing an RTB-based sintered magnet.   The method for producing an R-T-B system sintered magnet according to claim 1, wherein in the step of preparing the RH diffusion source, the RH diffusion source is polished, cut or crushed. The method for producing an RTB-based sintered magnet according to claim 1 or 2, wherein a stirring auxiliary member is inserted into the processing chamber before or during the RH diffusion step.

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