JP2014063792A - METHOD OF MANUFACTURING SURFACE-MODIFIED R-Fe-B-BASED SINTERED MAGNET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a surface-modified R-Fe-B-based sintered magnet which has superior corrosion resistance and superior surface adhesive properties.SOLUTION: The method of manufacturing a surface-modified R-Fe-B-based sintered magnet includes a process of creating an atmosphere of 1×10to 1×10Pa in oxygen partial pressure, less than 1000 Pa in partial water vapor pressure, and 1 to 20,000 (excluding 1) in ratio of the oxygen partial pressure and the partial water vapor pressure (oxygen partial pressure/partial water vapor pressure) so that a positive pressure state is produced in a processing chamber by introducing an atmosphere gas under conditions of 0.028 m/minute or higher in oxygen flow rate and 3 m/minute or lower in total flow rate for every capacity of 1 min the processing chamber, and subjecting the R-Fe-B-based sintered magnet to a heat treatment at 260-450°C in the processing chamber, the temperature of the magnet being lowered from the temperature at which the heat treatment is performed down to at least 100°C at an average cooling speed of 650°C/hour.

Description

  The present invention relates to a method for producing a surface-modified R—Fe—B sintered magnet having excellent corrosion resistance and excellent surface adhesion.

R-Fe-B-based sintered magnets are used in various fields today because they use resource-rich and inexpensive materials and have high magnetic properties, but they are highly reactive. Rare earth element: Since it contains R, it has the property of being easily oxidized and corroded in the atmosphere. Therefore, R-Fe-B based sintered magnets are usually put to practical use by forming a corrosion-resistant film such as a metal film or a resin film on the surface thereof.
In recent years, as a method for imparting corrosion resistance to an R—Fe—B based sintered magnet, a method of modifying the surface of the magnet by performing heat treatment (oxidation heat treatment) in an oxidizing atmosphere on the magnet has been attracting attention. Has been. For example, Patent Document 1 and Patent Document 2 describe a method of forming an oxidizing atmosphere using oxygen and performing a heat treatment, and Patent Documents 3 to 7 use water vapor alone, or A method is described in which oxygen is combined with water vapor to form an oxidizing atmosphere and heat treatment is performed. However, even if surface modification is performed on the magnet by these methods, the surface of the magnet is finely affected by fluctuations in temperature and humidity, such as in transportation and storage environments where temperature and humidity are not controlled. In an environment where repeated condensation occurs repeatedly, sufficient corrosion resistance is not always obtained. In Patent Documents 3 to 7, the water vapor partial pressure is preferably 10 hPa (1000 Pa) or more. When heat treatment is performed in an atmosphere with a high water vapor partial pressure, a large amount of hydrogen is generated as a by-product due to an oxidation reaction that occurs on the surface of the magnet, and the magnetic properties are reduced by occlusion and embrittlement of the hydrogen generated by the magnet. This has been clarified by the study of the present inventors. Therefore, the present inventors have proposed an oxygen partial pressure and a water vapor partial pressure of less than 10 hPa, which are considered inappropriate in Patent Documents 3 to 7, as a better surface modification method for R-Fe-B based sintered magnets. Is a heat treatment method in an oxidizing atmosphere appropriately controlled, specifically, an oxygen partial pressure of 1 × 10 ² Pa to 1 × 10 ⁵ Pa and a water vapor partial pressure of 0.1 Pa to 1000 Pa (excluding 1000 Pa) Patent Document 8 proposed a method of performing heat treatment at 200 ° C. to 600 ° C. in the atmosphere described above.

Japanese Patent No. 2844269 JP 2002-57052 A JP 2006-156853 A JP 2006-210864 A JP 2007-103523 A JP 2007-207936 A JP 2008-244126 A International Publication No. 2009/041639

  By the way, when an R—Fe—B based sintered magnet is used for a motor such as an SPM motor, the R—Fe—B based sintered magnet is bonded to a member such as a rotor with an adhesive. In particular, in the SPM motor, the magnet is bonded to the outer periphery of the rotor and is rarely buried in the resin, so that the surface of the R—Fe—B based sintered magnet is required to have good adhesion. However, according to the surface modification method for the R—Fe—B based sintered magnet proposed by the present inventors in Patent Document 8, the expected corrosion resistance improvement effect is obtained, while the adhesion of the magnet surface is the surface. It was found that it deteriorated slightly compared to before the reforming. Accordingly, an object of the present invention is to provide a method for producing a surface-modified R—Fe—B based sintered magnet having excellent corrosion resistance and excellent surface adhesion.

  When the inventors investigated the surface of a magnet having a low adhesive strength in an adhesive strength test for a magnet whose surface was modified by the surface modification method of Patent Document 8, many of them were cohesive failure of the adhesive. Some destruction of the magnet material itself was observed. For this reason, it is thought that one of the causes of adhesive deterioration may be that the surface modification layer becomes relatively brittle due to the heat treatment for surface modification, and further studies are made to eliminate this phenomenon. As a result, it has been found that it is effective to eliminate this phenomenon by performing heat treatment in a positive pressure environment and then rapidly lowering the temperature of the magnet.

The manufacturing method of the surface-modified R—Fe—B sintered magnet of the present invention completed based on the above findings has an oxygen partial pressure of 1 × 10 ³ Pa to 1 × as described in claim 1. An atmosphere having a water vapor partial pressure of less than 1000 Pa at 10 ⁵ Pa and an oxygen partial pressure to water vapor partial pressure ratio (oxygen partial pressure / water vapor partial pressure) of 1 to 20000 (excluding 1) is 0.028 m 3 ^/ min or more the introduction of the atmospheric gas per volume 1 m ³ as an oxygen flow, and formed as the processing by making the entire flow 3m 3 ^/ min under the following conditions chamber is a positive pressure state And a step of heat-treating the R—Fe—B-based sintered magnet at 260 ° C. to 450 ° C. in the processing chamber, and lowering the temperature of the magnet from the heat-treated temperature to at least 100 ° C. at 650 ° C. / Specially performed at an average cooling rate of over an hour It is a sign.
The manufacturing method according to claim 2 is characterized in that, in the manufacturing method according to claim 1, the average cooling rate is 2000 ° C./hour or less.
Moreover, the surface-modified R—Fe—B based sintered magnet of the present invention, as described in claim 3, is a surface-modified R—Fe produced by the production method according to claim 1 or 2. -B-based sintered magnet, wherein the surface-modified portion includes, in order from the inside of the magnet, a main layer containing α-Fe and amorphous R oxide as constituent components, at least R, Fe and oxygen. It is characterized by comprising a surface modification layer having at least three layers of an outermost layer containing an amorphous layer containing and iron oxide mainly composed of hematite as a constituent component.

  ADVANTAGE OF THE INVENTION According to this invention, while having the outstanding corrosion resistance, the manufacturing method of the surface-modified R-Fe-B type sintered magnet which has the outstanding surface adhesiveness can be provided.

It is the schematic (side view) of an example of the continuous processing furnace which can be suitably employ | adopted for the manufacturing method of the surface-modified R-Fe-B type sintered magnet of this invention. It is a chart which shows the X-ray photoelectron analysis result of the surface modification layer of the surface modified R-Fe-B system sintered magnet in the Example of this invention. It is the photograph of the low double bright field image by the transmission electron microscope of the surface modification layer of the surface-modified R-Fe-B system sintered magnet in the Example of this invention. It is a photograph of the high-resolution lattice image by the transmission electron microscope of the surface modification layer of the surface modified R-Fe-B system sintered magnet in the Example of this invention. It is a photograph of the electron beam diffraction pattern by the transmission electron microscope of the surface modification layer of the surface modified R-Fe-B system sintered magnet in the Example of this invention. It is a figure explaining the method to measure adhesive strength in the Example of this invention.

The method for producing a surface-modified R—Fe—B sintered magnet of the present invention has an oxygen partial pressure of 1 × 10 ³ Pa to 1 × 10 ⁵ Pa, a water vapor partial pressure of less than 1000 Pa, and oxygen An atmosphere having a ratio of partial pressure to water vapor partial pressure (oxygen partial pressure / water vapor partial pressure) of 1 to 20000 (excluding 1) is 0.028 m with the introduction of atmospheric gas per volume of 1 m ^{3 in the} processing chamber as an oxygen flow rate. ^The process chamber is formed to be in a positive pressure state by performing the process under conditions of ³ / min or more and a total flow rate of 3 m ³ / min or less, and the R-Fe-B based sintered magnet is formed in the process chamber. Including a step of performing heat treatment at 260 ° C. to 450 ° C., and lowering the temperature of the magnet from the heat-treated temperature at an average cooling rate of 650 ° C./hour or more until reaching at least 100 ° C. . Adhesion of the magnet surface by forming a predetermined oxidizing atmosphere by introducing atmospheric gas under predetermined conditions so that the processing chamber is in a positive pressure state and appropriately controlling the cooling rate after the heat treatment The surface modification desired for the R—Fe—B based sintered magnet can be performed without causing the deterioration.

The surface modified layer of the R-Fe-B sintered magnet subjected to the surface modification as described above mainly contains α-Fe and amorphous R oxide as constituent components in order from the inside of the magnet. A layer, an amorphous layer containing at least R, Fe, and oxygen, and an outermost layer containing iron oxide mainly composed of hematite (α-Fe ₂ O ₃ ) as a constituent component. Among the surface modified layers, the thickness of the main layer is, for example, 0.4 μm to 9.9 μm, the thickness of the amorphous layer is, for example, 100 nm or less, and the thickness of the outermost layer is, for example, 10 nm to 300 nm (surface The thickness of the entire modified layer is, for example, 0.5 μm to 10 μm), and the thickness of the main layer is approximately 80% to 99% of the entire surface modified layer. It is considered that the structure of the main layer included as a constituent component contributes to the excellent adhesiveness of the R—Fe—B based sintered magnet of the present invention. Patent Document 7 and Patent Document 8 also describe a specific structure of the surface modified layer. The surface modification layer of Patent Document 7 includes a first layer containing at least R, Fe and oxygen, an amorphous second layer containing at least R and oxygen, and a third layer containing at least Fe and oxygen. More specifically, the first layer includes an oxide of R and an oxide of Fe, and in the example, it is confirmed that the first layer is entirely crystalline. The structure of the first layer, that is, the main layer is different from the surface modified layer of the present invention. The surface modification layer of Patent Document 8 is mainly composed of a main layer containing R, Fe, B, and oxygen, an amorphous layer containing at least R, Fe, and oxygen, and hematite (α-Fe ₂ O ₃ ). Although it is described that it has at least three outermost layers containing iron oxide as a constituent component, the specific structure of the main layer is not described.

By to define the oxygen partial pressure in the step of performing a heat treatment with ^{1 × 10 3 Pa~1 × 10 5} Pa is the oxygen partial pressure is less than 1 × ¹⁰ 3 Pa, the oxygen content in the atmosphere is too low When the surface modification of the magnet takes too much time or when the magnet is disposed on the holding member and heat treatment is performed, the portion of the magnet that is in contact with the holding member is not sufficiently surface modified, This is because there is a risk that sufficient corrosion resistance and stability will not be imparted, or that traces of contact with the holding member may remain in the portion. On the other hand, even if the oxygen partial pressure is made higher than 1 × 10 ⁵ Pa, the improvement of the surface modification effect of the magnet by increasing the oxygen partial pressure is not recognized so much, which may only increase the cost. There is. In order to perform the desired modification on the surface of the magnet more effectively and at low cost, the oxygen partial pressure is preferably 1 × 10 ³ Pa to 5 × 10 ⁴ Pa, and 1 × 10 ⁴ Pa to ³ × 10. ⁴ Pa is more desirable.

The water vapor partial pressure is defined as less than 1000 Pa. If the water vapor partial pressure is 1000 Pa or more, the amount of water vapor in the atmosphere is excessive, and the surface of the magnet is modified to a stable one that exhibits excellent corrosion resistance. Or because of the oxidation reaction that occurs on the surface of the magnet, a large amount of hydrogen is generated as a byproduct, and the hydrogen generated by the magnet may be occluded, making the surface of the magnet brittle and deteriorating the adhesion. is there. In order to perform the desired modification on the surface of the magnet more effectively and at low cost, the water vapor partial pressure is desirably 700 Pa or less, and more desirably 45 Pa or less. The lower limit of the water vapor partial pressure is not particularly limited, but is usually 1 Pa.

The ratio between the oxygen partial pressure and the water vapor partial pressure is defined as 1 to 20000 (excluding 1) because when the ratio is 1 or less, the amount of water vapor with respect to the amount of oxygen in the atmosphere is too large. This is because the surface may not be modified to a stable one that exhibits excellent corrosion resistance. On the other hand, an atmosphere in which the ratio is greater than 20000 is a special environment and is not practical. In order to perform the desired modification on the surface of the magnet more effectively and at a low cost, the ratio is preferably 10 to 10,000, more preferably 300 to 5000, and further preferably 450 to 4000.

The atmosphere in the processing chamber may be formed by individually introducing oxygen or water vapor as an atmospheric gas so as to have a predetermined partial pressure, or an atmosphere having a dew point that includes these at a predetermined partial pressure is introduced. However, in any case, in the present invention, the atmosphere in the processing chamber is 0.028 m ³ / introduction of atmospheric gas per volume of 1 m ^{3 in the} processing chamber. It is formed so as to be in a positive pressure state in the processing chamber by performing it under the condition of not less than 3 minutes and not more than 3 m ³ / minute as a whole flow rate (having a dew point in which oxygen or water vapor is contained at a predetermined partial pressure as atmospheric gas) When the atmosphere is used, the oxygen flow rate is naturally controlled if the atmospheric flow rate is controlled as the total flow rate). The positive pressure in the processing chamber means that an inert gas having the same flow rate is introduced into the processing chamber separately and the oxygen concentration is zero or below the lower limit of measurement, that is, outside air does not enter the processing chamber. Can be confirmed. By forming the atmosphere in the processing chamber in this manner, a surface modified layer having excellent adhesion can be formed on the surface of the magnet. If the flow rate of oxygen introduced into the processing chamber is too small, the desired effect of improving adhesion cannot be obtained. It takes too much time to modify the surface of the magnet, and it is impossible to obtain the structure of the main layer containing α-Fe and amorphous R oxide as constituent components, and the entire main layer becomes a relatively brittle oxide. It is thought that this is because the internal stress increases and becomes brittle due to the increase in the proportion of oxygen taken in as a result. On the other hand, if the total flow rate is too large, the temperature distribution in the processing chamber will vary, and it may not be possible to perform uniform surface modification on all the magnets in the processing chamber. Note that an inert gas such as nitrogen gas or argon gas may coexist in the processing chamber.

  The temperature of the heat treatment is defined as 260 ° C. to 450 ° C. If the temperature is lower than 260 ° C., it may be difficult to perform the desired modification on the surface of the magnet, while the heat treatment temperature is higher than 450 ° C. This is because the magnetic properties of the magnet may be adversely affected. The temperature of the heat treatment is preferably 280 ° C to 430 ° C, more preferably 300 ° C to 420 ° C. The heat treatment time is preferably 1 minute to 3 hours, more preferably 15 minutes to 2.5 hours. If the time is too short, it may be difficult to perform the desired modification on the surface of the magnet, while if the time is too long, the magnetic properties of the magnet may be adversely affected.

In addition, it is desirable to perform the process of raising the temperature of the magnet from room temperature to the temperature at which heat treatment is performed in an atmosphere having an oxygen partial pressure of 1 × 10 ³ Pa to 1 × 10 ⁵ Pa and a water vapor partial pressure of 1 Pa to 100 Pa. By raising the temperature in such an atmosphere, moisture that is naturally adsorbed on the surface of the magnet is desorbed at an early stage, so that the moisture present on the surface of the magnet is It is possible to avoid adverse effects as much as possible. The average heating rate may be, for example, 100 ° C./hour to 2000 ° C./hour. In the present invention, “normal temperature” refers to the temperature (for example, room temperature) of the environment in which the R—Fe—B sintered magnet subjected to surface modification is placed at the start of temperature rise, and is illustrative. Means a temperature defined as 5 ° C. to 35 ° C. in JIS Z 8703 of the Japanese Industrial Standard.

  The step of lowering the temperature of the magnet after heat treatment (hereinafter referred to as the temperature drop step) is performed at an average cooling rate of 650 ° C./hour or more from the heat treatment temperature to at least 100 ° C. According to the study by the present inventors, the effect of improving the adhesiveness of the R-Fe-B sintered magnet surface-modified by performing the heat treatment under the above-described conditions is the cooling rate in the temperature lowering process after the heat treatment. The desired adhesion improvement effect cannot be obtained if the cooling rate is slow. This is because, due to the time required for cooling, the structure of the main layer containing α-Fe and amorphous R oxide formed by heat treatment under the above-mentioned conditions cannot be maintained, and surface modification is not possible. Like the case where it took too much time, it is presumed that the whole becomes a relatively brittle oxide. The upper limit of the average cooling rate is not particularly limited, but is preferably 2000 ° C./hour in order to lower the temperature at a low cost by a simple method. When the temperature of the magnet further decreases after reaching 100 ° C., the above average cooling rate may or may not be maintained. In addition, the temperature lowering process should be performed using the same atmosphere as that used in the temperature increasing process to prevent the phenomenon that the magnet surface corrodes and the magnetic properties deteriorate due to condensation on the surface of the magnet. It is desirable in that it can.

  The specific means for lowering the temperature of the magnet after the heat treatment at the above average cooling rate is not particularly limited. For example, a magnet is housed in a heat-resistant container made of a material such as SUS, Ti, Mo, Nb, etc. capable of controlling the atmosphere by circulating an atmosphere gas in the temperature raising process, the heat treatment process, and the temperature lowering process, When a heat-resistant container containing a magnet is housed in a processing chamber of a batch-type heat treatment furnace and the atmosphere inside the heat-resistant container is controlled, the flow rate of the atmospheric gas used in the temperature lowering process of the magnet is increased or the temperature is increased. By lowering the temperature, the magnet can be cooled at a desired average cooling rate. The temperature drop of the magnet at the desired average cooling rate can be achieved by opening the processing chamber containing the heat-resistant container containing the magnet to the atmosphere, reducing the number of magnets contained in the heat-resistant container, and the heat-resistant container containing the magnet. It can also be carried out by a method of taking out from the heat treatment furnace and cooling separately.

In addition, when performing a temperature raising process, a heat treatment process, and a temperature lowering process using a batch-type heat treatment furnace that can change the environment in the processing chamber in which the magnet is accommodated to an environment for sequentially performing each process, the magnet The magnet can be cooled at a desired average cooling rate by increasing the flow rate of the atmospheric gas used in the temperature lowering step or decreasing the temperature.

  Further, the temperature raising process, the heat treatment process, and the temperature lowering process are divided into regions controlled by the environment for performing the respective processes, and a continuous processing furnace (for example, FIG. 1) that can sequentially move the magnet to each region. When the temperature is lowered by using the above-described method, the temperature of the magnet can be lowered at a desired average cooling rate by appropriately controlling the temperature-lowering environment of the magnet in the temperature-lowering region. For example, in the continuous processing furnace shown in FIG. 1, each process is performed while moving the magnet from the left to the right in the figure by a moving means such as a belt conveyor. Arrows indicate the flow of the atmospheric gas in each region formed by an unillustrated air supply means and exhaust means. The inlet of the temperature rising region and the outlet of the temperature falling region are partitioned by, for example, an air curtain, and the boundary between the temperature rising region and the heat treatment region and the boundary between the heat treatment region and the temperature lowering region are partitioned by, for example, the flow of the atmospheric gas indicated by the arrows (these This may be done mechanically with a shutter). If such a continuous processing furnace is used, stable quality surface modification can be continuously performed for a large number of magnets, and the temperature of the magnet at the desired average cooling rate is the atmospheric gas used in the temperature-decreasing region. The flow rate can be increased to decrease the temperature, or the moving speed of the moving means can be adjusted.

  Even if the modified layer formed on the surface of the R—Fe—B based sintered magnet by the above process is very thin with a thickness of 1 μm or less (nanometer order), sufficient corrosion resistance is exhibited.

Examples of the R—Fe—B based sintered magnet to which the present invention is applied include those manufactured by the following manufacturing method.
An alloy including 25% by mass to 40% by mass of rare earth element R, 0.6% by mass to 1.6% by mass of B (boron), and the balance Fe and inevitable impurities is prepared. Here, R may contain a heavy rare earth element RH. Further, a part of B may be substituted by C (carbon), and a part of Fe (50% by mass or less) may be substituted by another transition metal element (for example, Co or Ni). Good. This alloy is suitable for a variety of purposes, including Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and About 0.01% by mass to 1.0% by mass of at least one additive element M selected from the group consisting of Bi may be contained.
The above-mentioned alloy can be suitably produced by rapidly cooling a molten raw material alloy by, for example, a strip casting method. Hereinafter, preparation of a rapidly solidified alloy slab by the strip casting method will be described.
First, a raw material alloy having the above composition is melted by high-frequency melting in an argon atmosphere to form a molten raw material alloy. Next, after holding this molten metal at about 1350 ° C., it is rapidly cooled by a single roll method to obtain, for example, a flake-shaped alloy slab having a thickness of about 0.3 mm. The alloy slab thus produced is pulverized into, for example, 1 mm to 10 mm flakes before the next hydrogen pulverization treatment. In addition, the manufacturing method of the alloy cast piece by a strip cast method is disclosed by the US Patent 5,383,978 specification, for example.
[Coarse grinding process]
The alloy slab coarsely crushed into flakes is accommodated in the hydrogen furnace. Next, a hydrogen embrittlement treatment process (hereinafter sometimes referred to as “hydrogen pulverization treatment” or simply “hydrogen treatment”) is performed inside the hydrogen furnace. When the coarsely pulverized powder after the hydrogen pulverization treatment is taken out from the hydrogen furnace, the takeout operation is preferably performed in an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere. By doing so, it is possible to prevent the coarsely pulverized powder from oxidizing and generating heat, and to suppress the deterioration of the magnetic properties of the magnet.
By the hydrogen pulverization treatment, the rare earth alloy is pulverized to a size of about 0.1 mm to several mm, and the average particle size becomes 500 μm or less. After the hydrogen pulverization treatment, the embrittled raw material alloy is preferably crushed more finely.
[Fine grinding process]
Next, the coarsely pulverized powder is finely pulverized in an inert gas atmosphere using a jet mill pulverizer. A cyclone classifier is connected to the jet mill crusher used in the present embodiment. The jet mill pulverizer is supplied with the rare earth alloy (coarse pulverized powder) coarsely pulverized in the coarse pulverization step, and pulverizes in the pulverizer. The powder pulverized in the pulverizer is collected in a collection tank through a cyclone classifier. Thus, a fine powder of about 0.1 μm to 20 μm can be obtained. The pulverizer used for such fine pulverization is not limited to a jet mill, and may be an attritor or a ball mill. In grinding, a lubricant such as zinc stearate may be used as a grinding aid.
[Press molding]
In the present embodiment, for example, 0.3% by mass of a lubricant is added to and mixed with the fine powder produced by the above method in a rocking mixer, and the surface of the finely pulverized powder particles is coated with the lubricant. Next, the finely pulverized powder produced by the above-described method is molded in an orientation magnetic field using a known press apparatus. The strength of the applied magnetic field is, for example, 1.0T to 1.7T. Further, the molding pressure is set as green density of the compact is, for example, about ^{4g / cm 3 ~4.5g / cm 3} .
[Sintering process]
For example, it is performed on the above powder compact at a temperature in the range of 1000 ° C. to 1200 ° C. for 10 minutes to 240 minutes. A step of holding for 10 minutes to 240 minutes at a temperature in the range of 650 ° C. to 1000 ° C., and a step of further proceeding with sintering at a temperature higher than the above holding temperature (for example, 1000 ° C. to 1200 ° C.) sequentially. You may go. During sintering, particularly when the temperature is in the range of 650 ° C. to 1000 ° C., the R-rich phase in the grain boundary phase begins to melt and a liquid phase is formed. Thereafter, the sintering proceeds and a sintered body is formed. After the sintering step, aging treatment (400 ° C. to 700 ° C.) and grinding for dimension adjustment may be performed.

  The surface-modified R—Fe—B sintered magnet produced by the production method of the present invention has excellent corrosion resistance imparted by an oxidation heat treatment and has excellent surface adhesion. For example, it is suitable for use in an IPM motor that is used as an SPM motor such as an EPS motor for automobiles, a drive motor for a hybrid vehicle or an electric vehicle, or incorporated in a compressor of an air conditioner. In addition, when manufacturing an SPM motor using the surface-modified R—Fe—B sintered magnet manufactured by the manufacturing method of the present invention, the magnet may be attached to the outer periphery of the rotor with an adhesive. . Of course, you may reinforce by winding a metal wire etc. after adhesion. When manufacturing an IPM motor, it may be performed through a step of embedding a magnet in the rotor.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is limited to this and is not interpreted.

(Manufacture of magnet test piece 1)
Nd: 19.0, Pr: 5.5, Dy: 8.2, B: 0.97, Co: 0.9, Cu: 0.1, Al: 0.2, Ga: 0.09, balance: An alloy slab having a composition of Fe (unit: mass%) and having a thickness of 0.2 mm to 0.3 mm was produced by strip casting.
Next, this alloy slab was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with hydrogen gas at a pressure of 500 kPa, so that hydrogen was occluded in the alloy slab at room temperature and then released. By performing such a hydrogen treatment, the alloy slab was embrittled and a coarsely pulverized powder having a size of about 0.15 mm to 0.2 mm was produced.
After adding 0.04 mass% zinc stearate as a pulverization aid to the coarsely pulverized powder produced by the above hydrogen treatment and mixing, a pulverization step using a jet mill device is performed to obtain a fine particle diameter of about 3 μm. A powder was prepared.
The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus, and a sintering process was performed at 1050 ° C. for 4 hours in a vacuum furnace to obtain a sintered body block.
The obtained sintered body block was subjected to an aging treatment at 490 ° C. for 2.5 hours in a vacuum, and then the surface was ground to adjust the dimensions, and the thickness was 4 mm × length 15 mm × width 18 mm. A sintered magnet (hereinafter referred to as “magnet body test piece 1”) was obtained.
(Manufacture of magnet body test piece 2)
Nd: 16.2, Pr: 4.5, Dy: 9.1, B: 0.93, Co: 2.0, Cu: 0.1, Al: 0.15, Ga: 0.07, balance: An alloy slab having a composition of Fe (unit: mass%) having a thickness of 0.2 mm to 0.3 mm was produced by a strip cast method, and a sintered body block was obtained in the same manner as the production of the magnet body test piece 1. . R-Fe-B sintered magnet having a thickness of 4 mm x length of 15 mm x width of 18 mm (hereinafter referred to as "magnet body test piece 2") in the same manner as the production of the magnet body test piece 1 from the obtained sintered body block. Got.

Example 1
After magnet body test piece 1 was ultrasonically washed, surface modification was performed using a continuous processing furnace having the configuration shown in FIG. The temperature of the sintered magnet was measured by monitoring the temperature of a temperature measuring magnet equipped with a thermocouple.
(1) Temperature rising step The temperature is raised from room temperature (25 ° C., the same applies hereinafter) to the temperature at which heat treatment is performed (400 ° C.). The atmosphere has a dew point of −40 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 19 Pa, oxygen partial pressure / The reaction was carried out at an average temperature increase rate of 500 ° C./hour in an atmosphere of water vapor partial pressure = 1052).
(2) Heat treatment step The heat treatment step was carried out at 400 ° C. for 20 minutes in an atmosphere having an dew point of 0 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 600 Pa, oxygen partial pressure / water vapor partial pressure = 33.3). The formation of the atmosphere in the heat treatment region (corresponding to the treatment chamber in the present invention: volume 0.64 m ³ ) is achieved by introducing air with a dew point of 0 ° C. into the heat treatment region at a flow rate of 0.120 m ³ / min. (The oxygen flow rate per volume of 1 m ³ is 0.037 m ³ / min and the total flow rate is 0.188 m ³ / min. The oxygen flow rate is 1/5 of the atmospheric flow rate that is the total flow rate. Conversion: Atmospheric flow rate is controlled by an area-type flow meter, and heat treatment is started after 30 minutes or more from the start of introduction of atmospheric gas. Confirmation of the positive pressure state is carried out by separately introducing an inert gas having the same flow rate as the above-mentioned overall flow rate into the heat treatment region, and confirming that the oxygen concentration is below the lower limit of measurement 30 minutes after the start of introduction, It was confirmed that the processing chamber was positive pressure.
(3) Temperature-falling step Under the same atmosphere adopted in the temperature-raising step, the temperature was lowered from 400 ° C. to 100 ° C. at an average cooling rate of 690 ° C./hour. The average cooling rate was adjusted by adjusting the flow rate of the atmospheric gas used for cooling.
The thickness of the modified layer formed on the surface of the sintered magnet by the above method was 1.5 μm. The thickness of the modified layer was determined by preparing a sample using an ion beam cross-section processing device (SM09010: manufactured by JEOL Ltd.) after embedding and polishing a surface-modified sintered magnet, and then using a field emission scanning electron microscope ( S-4300 (manufactured by Hitachi High-Technology Corporation) was used for cross-sectional observation (hereinafter the same).

  About the sintered magnet surface-modified by the above method, the cross-sectional observation of the surface vicinity is observed with a transmission electron microscope (TEM: HF2100: manufactured by Hitachi High-Technology Corporation) Energy dispersive X-ray analyzer (EDX: manufactured by NORAN) As a result of using a scanning electron microscope (FE-SEM: S-4300: manufactured by Hitachi High-Technology Co., Ltd.), the main layer having a thickness of about 1.4 μm and the R and Fe having a thickness of about 50 nm were sequentially formed from the magnet surface. 3 of an amorphous layer containing Fe and oxygen (Fe—R oxide and / or amorphous layer containing Fe oxide and R oxide) and a Fe oxide layer having a thickness of about 150 nm and substantially free of R It was found to have a layer structure. Moreover, the result of having analyzed the magnet surface vicinity using the X-ray photoelectron analyzer (ESCA-850M: SHIMADZU company make) is shown in FIG. It was found that Fe in the main layer was in a metallic state and R was an oxide.

The results of cross-sectional observation of the main layer using a transmission electron microscope (JEM-3010: manufactured by JEOL Ltd.) are shown in FIGS. 3 is a low-magnification bright-field image of the entire surface modified layer, FIG. 4 is a high-resolution lattice image near the arrow tip of the main layer in FIG. 3, and FIG. 5 is from the φ100 nm region near the arrow tip of the main layer in FIG. It is the obtained electron beam diffraction pattern. It can be seen from the low-magnification bright-field image of FIG. 3 that a columnar main layer is formed in the upper layer of the Nd ₂ Fe ₁₄ B type crystal phase that appears to be striped. In the low-magnification bright-field image of FIG. 3, the amorphous layer containing R, Fe, and oxygen having a thickness of about 50 nm is too thin to be distinguished. The white part in the center is a hole made at the time of sample preparation. FIG. 4 shows a high-resolution observation result near the tip of the arrow in the main layer of FIG. It can be seen that an amorphous phase of about 2 to 5 nm is dispersed in the lattice of the matrix of the base material (it can be determined that the lattice is broken, so that it is amorphous. For example, a circled portion in FIG. Crystalline phase). Further, the electron diffraction pattern of FIG. 5 is obtained from the matrix of the base material, and since the diffraction pattern can be attributed to α-Fe, it can be seen that the base material matrix is α-Fe. Since the amorphous phase finely dispersed in the matrix of the matrix is very small, it is very difficult to understand as a spot of the diffraction pattern, but it is judged based on the results of X-ray photoelectron analysis and energy dispersive X-ray analysis. Then, the amorphous phase is considered to be an R oxide. That is, the main layer includes α-Fe and amorphous R oxide as constituent components, and specifically has a structure in which amorphous R oxide is dispersed in α-Fe. I found out.

Further, as a result of examining the vicinity of the outermost layer using an X-ray diffraction analyzer (RINT2400: manufactured by Rigaku), an Fe oxide layer having a thickness of about 150 nm and containing substantially no R is hematite (α-Fe ₂ O ₃ ).

(Example 2)
The sintered magnet was prepared in the same manner as in Example 1 except that the heat treatment step was performed in an atmosphere with a dew point of −40 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 19 Pa, oxygen partial pressure / water vapor partial pressure = 1052). Surface modification was performed. (The confirmation of the positive pressure state is also the same as in Example 1.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.3 μm.

(Example 3)
By using a batch-type heat treatment furnace having a volume of 0.0034 m ^{3 in} the processing chamber and introducing an atmosphere having a dew point of 0 ° C. into the processing chamber at a flow rate of 0.0041 m ³ / min, It was performed in a positive pressure state (the oxygen flow rate per volume of 1 m ³ was 0.238 m ³ / min and the total flow rate was 1.209 m ³ / min.), And the heat treatment was performed for 5 minutes or more from the start of the introduction of the atmospheric gas. The surface modification of the sintered magnet was performed in the same manner as in Example 1 except that it started after the lapse of time and the temperature was lowered to 100 ° C. at an average cooling rate of 700 ° C./hour. The positive pressure state is confirmed by introducing an inert gas having the same flow rate as the above overall flow rate into the heat treatment region, and confirming that the oxygen concentration is below the lower limit of measurement 5 minutes after the start of introduction. It was confirmed that the room was positive pressure. As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.4 μm.

Example 4
The surface modification of the sintered magnet was performed in the same manner as in Example 3 except that the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber. (The confirmation of the positive pressure state is also the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.4 μm.

(Example 5)
Except that the atmosphere in the processing chamber was formed by introducing an atmosphere with a dew point of −40 ° C. at a flow rate of 0.0030 m ³ / min into the processing chamber (the oxygen flow rate per volume of 1 m ³ was 0.176 m ³ / min. The overall flow rate was 0.894 m ³ / min.) Surface modification of the sintered magnet was performed in the same manner as in Example 3. (The confirmation of the positive pressure state is also the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.3 μm.

(Example 6)
Except that the atmosphere in the processing chamber was formed by introducing an atmosphere with a dew point of −40 ° C. at a flow rate of 0.0101 m ³ / min into the processing chamber (the oxygen flow rate per volume of 1 m ³ was 0.588 m ³ / min. The overall flow rate was 2.988 m ³ / min.) Surface modification of the sintered magnet was performed in the same manner as in Example 3. (Confirmation of the positive pressure state is the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.5 μm.

(Example 7)
The surface of the sintered magnet was formed in the same manner as in Example 3 except that the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber and that the heat treatment step was performed at 340 ° C. for 60 minutes. Modification was performed. (The confirmation of the positive pressure state is also the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.1 μm.

(Example 8)
The surface of the sintered magnet was formed in the same manner as in Example 3 except that the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber and the heat treatment step was performed at 300 ° C. for 120 minutes. Modification was performed. (The confirmation of the positive pressure state is also the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.2 μm.

Example 9
The magnetic body test piece 2 was used, the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber, the heat treatment step was performed at 420 ° C. for 20 minutes, and the temperature up to 100 ° C. The surface modification of the sintered magnet was performed in the same manner as in Example 3 except that the temperature was lowered at an average cooling rate of 900 ° C./hour. (Confirmation of the positive pressure state is the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.6 μm.

(Example 10)
The magnetic body test piece 2 was used, the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber, the heat treatment step was performed at 420 ° C. for 20 minutes, and the temperature up to 100 ° C. The surface modification of the sintered magnet was performed in the same manner as in Example 3 except that the temperature was lowered at an average cooling rate of 650 ° C./hour. (Confirmation of the positive pressure state is the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.8 μm.

(Example 11)
The same method as in Example 3 except that the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber and that the temperature was lowered to 100 ° C. at an average cooling rate of 1800 ° C./hour. The surface modification of the sintered magnet was performed. (The confirmation of the positive pressure state is also the same as in Example 3.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.3 μm.

(Comparative Example 1)
Except that the atmosphere in the processing chamber was formed by introducing an atmosphere with a dew point of 0 ° C. at a flow rate of 0.0004 m ³ / min into the processing chamber (the oxygen flow rate per volume of 1 m ³ was 0.022 m ³ / min. The flow rate was 0.112 m ³ / min.) Surface modification of the sintered magnet was performed in the same manner as in Example 3. As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.1 μm. The positive pressure state was confirmed by introducing an inert gas at the same flow rate as the above overall flow rate into the heat treatment region and confirming the oxygen concentration, but the oxygen concentration was measured even after 5 minutes or more after the introduction of the inert gas. The lower limit was not reached, and it was confirmed that the processing chamber was not positive.

(Comparative Example 2)
The surface modification of the sintered magnet was performed in the same manner as in Comparative Example 1 except that the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber. (The confirmation of the positive pressure state is also the same as in Comparative Example 1.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.2 μm.

(Comparative Example 3)
Except that the atmosphere was formed in the processing chamber by introducing an atmosphere with a dew point of −40 ° C. at a flow rate of 0.0151 m ³ / min into the processing chamber (the oxygen flow rate per volume of 1 m ³ was 0.882 m ³ / min. The total flow rate was 4.482 m ³ / min.) Surface modification of the sintered magnet was performed in the same manner as in Comparative Example 1. The positive pressure state is confirmed by introducing an inert gas having the same flow rate as the above overall flow rate into the heat treatment region, and confirming that the oxygen concentration is below the lower limit of measurement 5 minutes after the start of introduction. It was confirmed that the room was positive pressure. As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.5 μm.

(Comparative Example 4)
The magnetic body test piece 2 was used, the atmosphere in the processing chamber was formed by introducing air having a dew point of −40 ° C. into the processing chamber, the heat treatment step was performed at 420 ° C. for 20 minutes, and the temperature up to 100 ° C. The surface modification of the sintered magnet was performed in the same manner as in Example 1 except that the temperature was lowered at an average cooling rate of 420 ° C./hour. (Confirmation of the positive pressure state is also the same as in Example 1.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.6 μm.

(Comparative Example 5)
The surface modification of the sintered magnet was performed in the same manner as in Comparative Example 4 except that the temperature was lowered to 100 ° C. at an average cooling rate of 530 ° C./hour. (The confirmation of the positive pressure state is also the same as in Comparative Example 4.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.6 μm.

(Comparative Example 6)
The atmosphere in the processing chamber was formed by introducing air having a dew point of 15 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 1711 Pa, oxygen partial pressure / water vapor partial pressure = 11.7) into the processing chamber. The surface modification of the sintered magnet was performed in the same manner as in Example 1 except that the temperature was lowered at an average cooling rate of 700 ° C./hour. (The confirmation of the positive pressure state is also the same as in Example 1.) As a result, the thickness of the modified layer formed on the surface of the sintered magnet was 1.7 μm.

(Reference example)
After the magnet body test piece 1 was washed, the surface modification was not performed and the magnet body test piece was obtained.

(Corrosion resistance evaluation)
With respect to the sintered magnets subjected to surface modification in each of Examples 1 to 11 and Comparative Examples 1 to 6 and the sintered magnet of the reference example, the temperature was 60 ° C. and the relative humidity was 90% under high temperature and high humidity conditions. The corrosion resistance test was conducted for 24 hours, and the presence or absence of surface rust after the test was examined by appearance observation. Table 1 shows the number of magnets on which surface rusting was observed among the 20 magnets subjected to the test.

(Adhesive strength evaluation)
Using sintered hard magnet G55 (acrylic) manufactured by Denki Kagaku Kogyo Co., Ltd. as the adhesive, surface-modified in each of Examples 1 to 11 and Comparative Examples 1 to 6, and the sintered magnet of the reference example After bonding to an iron jig as shown in FIG. 6, the adhesive strength was examined by a method of punching out at a speed of 2 mm / min. The adhesion thickness is about 20 μm and the adhesion area is about 2 cm ² . The adhesive strength is shown in Table 1.

(Summary)
As is clear from the corrosion resistance evaluation results, the corrosion resistance imparted by the surface modification of the sintered magnet is not different between Examples 1 to 11, Comparative Examples 1, 2, 4, 5, and Reference Examples. In Comparative Examples 3 and 6, the corrosion resistance was inferior to these. In Comparative Example 3, since the introduction flow rate of the atmospheric gas was too large, it was considered that the temperature and atmosphere varied in the processing chamber and the surface modification varied, and Comparative Example 6 had a high water vapor partial pressure. This is thought to be due to the heat treatment performed in the atmosphere. In addition, as is apparent from the adhesive strength evaluation results, Examples 1 to 11 have an adhesive strength equivalent to that of the reference example without surface modification, but Comparative Examples 1, 2, 4 to 6 are bonded. The strength was reduced. When observing the adhesive surface after the adhesive strength test, in Examples and Reference Examples, almost the entire material was cohesive failure of the adhesive, while in the comparative example, some material destruction of the magnet surface was seen, Examples, It turned out that the magnet surface of a comparative example is weak with respect to the magnet surface of a reference example. While the adhesive strength test results of the examples were not different from those of the reference examples, the reasons why the adhesive strength test results of the comparative examples were inferior were as follows. This is because the structure of the layer is different between the example and the comparative example. That is, the magnets of Examples 1 to 11 were heat-treated in a positive pressure environment with a large oxygen flow rate, and the main layer of the surface modification layer was amorphous in α-Fe as described in Example 1. It has a structure in which R oxide is dispersed. The details of how such a surface-modified layer is formed are unknown, but the surface-modifying reaction in the present invention is an oxidation reaction accompanying the diffusion of oxygen into the magnet, and R-Fe-B by oxygen. The main phase of the sintered magnet is decomposed and disproportionated. At this time, by performing heat treatment in a positive pressure environment with high oxidizability, the diffusion rate of oxygen into the magnet is increased, and R having relatively high reactivity is preferentially oxidized, so that Fe of the main phase is oxidized. Atoms are hardly oxidized and change to α-Fe. The oxidized R is dispersed while remaining in α-Fe, and a disproportionation reaction due to oxidation proceeds inside the magnet. Since oxidation is promoted on the surface and α-Fe is oxidized, an iron oxide layer mainly composed of α-Fe ₂ O ₃ (hematite) is deposited on the outermost surface. At this time, since the R oxide present in α-Fe is not oxidized any more, it is concentrated under the iron oxide layer mainly composed of hematite (the outermost layer), and in order from the magnet surface, the iron oxide layer mainly composed of hematite, It is presumed that an amorphous layer containing R, Fe and oxygen is formed. In addition, since the cooling rate is fast, the temperature reaches normal temperature while maintaining the state. On the other hand, when heat treatment is performed in an atmosphere with a low oxygen flow rate and not a positive pressure as in Comparative Examples 1 and 2, the diffusion rate of oxygen into the interior slows down and the oxidation of α-Fe proceeds, and the main layer has R It is considered that Fe oxide that is more brittle than α-Fe is produced together with the oxide, and the entire main layer becomes brittle than the surface modified layer of the example. Furthermore, in this case, a large amount of oxygen is taken into the main layer, and it is considered that the main layer becomes brittle due to an increase in internal stress. In Comparative Examples 4 and 5 where the cooling rate in the temperature lowering process is slow, the structure of the formed main layer cannot be maintained in the temperature lowering process, and it is considered that the main layer became brittle because Fe oxidation progressed. In Comparative Example 6 in which the water vapor partial pressure exceeds 1000 Pa, it is considered that the magnet surface became brittle as the magnet occluded hydrogen generated as a result of oxidation by water vapor. For these reasons, it is considered that the magnet of the comparative example had a material fracture on the surface of the magnet in the adhesive strength evaluation test and the adhesive strength was lowered.

The surface-modified R—Fe—B sintered magnet produced by the production method of the present invention has excellent corrosion resistance imparted by an oxidation heat treatment and has excellent surface adhesion. For example, it is suitable for use as an IPM motor that is used as an SPM motor such as an EPS motor for automobiles, a drive motor for hybrid cars or electric cars, or incorporated in a compressor of an air conditioner. Has industrial applicability.

Claims (3)

A method for producing a surface-modified R—Fe—B sintered magnet having an oxygen partial pressure of 1 × 10 ³ Pa to 1 × 10 ⁵ Pa, a water vapor partial pressure of less than 1000 Pa, and an oxygen content 0.028m atmosphere of the ratio of pressure and water vapor partial pressure (oxygen partial pressure / water vapor partial pressure) is 1 to 20,000 (excluding proviso 1), the introduction of the atmospheric gas per volume 1 m ³ of the processing chamber as the oxygen flow rate ³ / Min. And at a total flow rate of 3 m ³ / min or less, the process chamber is formed to be in a positive pressure state. The R—Fe—B-based sintered magnet is 260 in the process chamber. The manufacturing method characterized by including the process of heat-processing at a C-450 degreeC, and performing the temperature fall of the magnet from the temperature which heat-processed at an average cooling rate of 650 degrees C / hr or more until it reaches at least 100 degreeC.   The manufacturing method according to claim 1, wherein the average cooling rate is 2000 ° C./hour or less. A surface-modified R-Fe-B sintered magnet manufactured by the manufacturing method according to claim 1 or 2, wherein the surface-modified portions are sequentially formed from the inside of the magnet. , At least 3 of a main layer containing α-Fe and amorphous R oxide as a constituent, at least an amorphous layer containing R, Fe and oxygen, and an outermost layer containing iron oxide mainly composed of hematite as a constituent A magnet comprising a surface modification layer having a layer.