JP6432406B2 - R-T-B system alloy powder and R-T-B system sintered magnet - Google Patents

Description

  The present invention relates to an RTB-based alloy powder and an RTB-based sintered magnet.

  R-T-B based sintered magnets (R is a rare earth element including Y, T is a transition element containing Fe as a main component, specifically Fe or Fe and Co, and B is boron) Since it has the highest magnetic energy product among them and its price is relatively low, it is widely used in various electronic devices.

  The RTB-based sintered magnet is produced by, for example, the following process.

  First, a raw material alloy is manufactured by casting various raw metals by a method such as an ingot method or a strip cast method. Next, the obtained raw material alloy is subjected to a pulverization step to obtain an alloy powder having a predetermined particle size. This pulverization process usually includes a coarse pulverization process and a fine pulverization process. The former uses, for example, a hydrogen embrittlement phenomenon, and the latter uses, for example, an airflow pulverizer (jet mill). Done.

  Next, the powder is subjected to a molding process in a magnetic field in which the powder is press-molded into a desired shape. By sintering the molded body thus obtained, an RTB-based sintered magnet is produced. Further, after sintering, heat treatment is usually performed.

  Various methods have been proposed to improve the coercive force of the RTB-based sintered magnet.

Patent Document 1 discloses RE ₂ TM ₁₄ B (where RE is one or more elements selected from Y, Sc and lanthanoids, and TM is one or more elements selected from Fe, Co and Ni) After the powder composed of two or more elements) is coated with a RE-TM alloy having a lower melting point (here, RE is the same as above), and this raw material powder is compression-molded Discloses a manufacturing method for sintering. By using this raw material powder, a magnet having high magnetic properties and high corrosion resistance can be obtained.

  Patent Document 2 is a process in which a powder containing neodymium, iron and boron is contacted with a vapor containing a metal selected from the group consisting of dysprosium, terbium, iron, and alloys thereof to form a coating powder; And a step of forming a permanent magnet from the coating powder.

JP-A-4-345002 JP2013-243346A

  In the techniques described in Patent Documents 1 and 2, since a powder is once produced and then coated with a metal film, an increase in oxygen content is unavoidable and it is difficult to produce a high-performance sintered magnet. It is.

  In addition, in the techniques described in Patent Documents 1 and 2, two steps of pulverization and coating or coating are necessary.

  The present invention has been made in view of the above problems, and is an alloy powder produced by a fine pulverization process, and an RTB-based alloy powder having a rare earth element enriched layer on the surface thereof, and It is an object of the present invention to provide an RTB-based sintered magnet produced by using the same.

  In the RTB-based alloy powder according to the embodiment of the present invention, the particle surface is covered with an R enriched layer containing at least one rare earth element selected from Nd, Pr, Dy, and Tb. The R-TB alloy powder is characterized in that the rare earth element concentration in the R enriched layer is in the range of 20 atomic% to 32 atomic%.

  In one embodiment, the oxygen concentration in the thickness direction of the R enriched layer decreases uniformly from the particle surface toward the inside.

In one embodiment, the R enriched layer further contains Fe, and the concentration of Fe in the R enriched layer is lower than the concentration of Fe in the R ₂ Fe ₁₄ B phase inside the R enriched layer.

In one embodiment, the R enriched layer further contains B, and the concentration of B in the R enriched layer is lower than the concentration of B in the R ₂ Fe ₁₄ B phase inside the R enriched layer.

  The RTB-based sintered magnet according to the embodiment of the present invention is obtained as a sintered body produced using the above RTB-based alloy powder.

  According to the embodiment of the present invention, an RTB-based alloy powder covered with an R-enriched layer and an RTB-based sintered magnet having a high coercive force can be provided.

(A) is a SEM photograph of the RTB system alloy powder by embodiment of this invention, (b) is a SEM photograph of the RTB system alloy powder of a comparative example. (C) and (d) are Nd element mapping photographs in the same field of view as (a) and (b), respectively. It is a graph which shows the density | concentration change of each component element from the particle | grain surface of the RTB type | system | group alloy powder by embodiment of this invention. It is a schematic diagram which shows the swirl | flow type crushing apparatus used by embodiment of this invention, (a) is side surface sectional drawing, (b) is Z-Z 'sectional drawing of (a).

[RTB-based alloy powder]
The RTB-based alloy powder according to an embodiment of the present invention has a surface covered with an R enriched layer containing at least one rare earth element of Nd, Pr, Dy, and Tb, and the R The concentration of the rare earth element in the concentrated layer is in the range of 20 atomic% to 32 atomic%.

  In the R enriched layer, the oxygen concentration in the thickness direction decreases uniformly from the particle surface toward the inside.

The R enriched layer further contains Fe, and the Fe concentration in the R enriched layer is lower than the Fe concentration in the R ₂ Fe ₁₄ B phase inside the R enriched layer.

The R enriched layer further contains B, and the concentration of B in the R enriched layer is lower than the concentration of B in the R ₂ Fe ₁₄ B phase inside the R enriched layer.

  By further including Fe and B, which are the main elements usually contained in the liquid phase of the RTB-based sintered magnet, the dispersibility of the R-rich phase in the sintered body can be achieved within a wide range of sintering temperatures. This increases the grain boundary of the sintered body.

  Preferably, the R concentrated layer has a thickness of 30 nm or more and 90 nm or less.

The R concentrated layer covers the surface of the particles. The presence of the R-enriched layer on the surface of the RTB-based alloy powder results in the formation of a uniform R-rich phase at the grain boundary after sintering, effectively suppressing the occurrence of reverse magnetic domains. The coercive force H _cJ is greatly improved.

  The composition of the alloy powder is 27.5% by mass or more and 36.0% by mass or less of R (R is at least one of rare earth elements, and at least one of Nd, Pr, Dy, and Tb must be used. 0.85 mass% to 1.05 mass% B and the balance T (T is a transition element mainly composed of Fe, specifically Fe or Fe and Co).

  When the concentration of R is less than 27.5% by mass, it is difficult to generate a liquid phase in the sintering process. On the other hand, when the concentration of R exceeds 36.0% by mass, the magnetization of the RTB-based sintered magnet is significantly reduced. The concentration of R is preferably 28.5% by mass or more and 33.0% by mass.

  If the concentration of B is less than 0.85% by mass, a soft magnetic phase is generated, which may reduce the coercive force of the RTB-based sintered magnet. On the other hand, when the concentration of B exceeds 1.05% by mass, a nonmagnetic phase is generated, and the magnetization of the RTB-based sintered magnet is lowered. The concentration of B is preferably 0.90% by mass or more and 1.05% by mass or less.

  The RTB-based alloy powder according to the embodiment of the present invention further includes a known additive element M (M is Al, Ti, V, Cr, Mn, 0.1 wt% or more and 2.5 wt% or less). And at least one selected from the group consisting of Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi. The additive element M can be added in a range of 2.5 mass% or less that does not cause a significant decrease in magnetization. The range of the element M is preferably 0.25% by mass or more and 0.9% by mass or less. M is preferably composed of at least one selected from the group consisting of Al, Cu, Ga, Zr, and Nb.

  T is the balance. T is a transition element mainly composed of Fe, and may contain Co. T is Fe or Fe and Co, and Fe accounts for 50 atomic% or more of the total of Fe and Co.

  The RTB-based alloy powder according to the embodiment of the present invention preferably has an oxygen content of 0.3% by mass or less. By reducing the oxygen content of the RTB-based alloy powder, the coercive force of the RTB-based sintered magnet can be increased.

  Inevitable impurities include C, N, H, Si, Ca, S, P, and the like. In any case, in order to improve the performance of the magnet, it is preferable to keep the content as small as possible in an industrially possible range.

[RTB sintered magnet]
The RTB-based sintered magnet according to the embodiment of the present invention is obtained as a sintered body produced using the RTB-based alloy powder.

[Method for producing RTB-based alloy powder]
The RTB-based alloy powder according to the embodiment of the present invention, for example, while rotating the coarse powder of the alloy in the composition range in the pulverization tank of the pulverizer, collision between the powders, grinding between the powders, Friction between the powder and the pulverization tank wall surface and R-rich ultrafine particles adhere to the particles of the alloy powder, and are produced by fine pulverization.

  Hereinafter, although the manufacturing method of the RTB type | system | group alloy powder by embodiment of this invention is demonstrated, referring drawings, this invention is not limited to the following embodiment.

[Mother alloy]
The alloy may be produced by either an ingot method or a strip cast method, but is preferably produced by a strip cast method which is a rapid cooling method. Thereby, α-Fe does not remain in the cast structure and can be easily pulverized. The composition of the mother alloy may be appropriately determined in consideration of the reduction of each element in the intermediate process so that the composition of the alloy powder to be produced has a predetermined composition.

[Crushing]
The pulverization process includes a two-stage pulverization process including a coarse pulverization process and a fine pulverization process.

  First, the coarse pulverization step will be described. The coarse pulverization of the mother alloy can be performed by a mechanical pulverization method or a hydrogen pulverization method.

Among these, it is preferable to coarsely pulverize the master alloy by a hydrogen pulverization method using a hydrogen embrittlement phenomenon. This method utilizes the embrittlement phenomenon and volume expansion phenomenon of the alloy that accompany hydrogen occlusion to generate fine cracks in the mother alloy and pulverize the mother alloy. According to the hydrogen pulverization method, the probability of cracking at the grain boundary increases. When the probability of cracking at the grain boundary increases, the number of main phase crystals (2-14-1 compound) contained in the grain becomes one, and the easy magnetization direction becomes one direction. Therefore, the magnetic field orientation becomes easy and the residual magnetic flux density B _r. Will improve.

The hydrogen pulverization method is performed, for example, by exposing to pressurized hydrogen for a certain period of time at room temperature. Next, the temperature is raised to release excess hydrogen and then cooled. The alloy powder after hydrogen embrittlement contains a large number of cracks, and the specific surface area is greatly increased. For this reason, it is very active, and the amount of oxygen increases remarkably when handled in the atmosphere. Therefore, it is desirable to handle in an inert gas such as N ₂ or Ar. The particle size of the alloy powder obtained by the coarse pulverization step is, for example, 500 μm or less.

  Note that, after the coarse pulverization step and before the fine pulverization step, which will be described later, for example, the particle size may be set to a specific range or less using a sieve or the like.

  Next, in the fine pulverization step, the alloy powders are swirled in the pulverization tank of the pulverizer, the powders collide with each other, the powders are ground, the friction between the powder and the pulverization tank wall surface, and the R-rich ultrafine particles are alloyed. By adhering to powder particles, it is finely pulverized.

  As an example, a fine pulverization process using a swirl flow pulverizer will be described below.

In the airflow pulverization method using a swirl flow pulverizer, a high-pressure pulverization gas is introduced into a pulverization tank provided in the pulverizer. As a result, a gas flow swirling at high speed is generated inside the pulverization tank, and the alloy powder is swirled in the pulverization tank by this gas flow. The alloy powder is finely pulverized by grinding during swirling by a pulverization method using a swirling flow pulverizer. As the pulverization gas, N ₂ gas is generally used, but a rare gas such as He or Ar gas may be used.

  In the present specification, the swirl type pulverizer is an air flow type pulverizer generally referred to as a jet mill, which is mainly pulverized by a swirl force, more specifically, a device capable of obtaining a grinding effect. Widely include.

  The gas pressure introduced into the pulverization tank means a gauge pressure (difference from atmospheric pressure).

  The residence time is defined as the time from the start of supply from the coarsely pulverized powder supply nozzle until the alloy powder is confirmed in the collection container (not shown).

  The pressure of the pulverization gas is preferably set to 0.75 MPa or more in terms of gauge pressure. More preferably, it is 0.75 MPa or more and 1.5 MPa or less, More preferably, it is 0.75 MPa or more and 0.95 MPa or less.

  The residence time is preferably 5 minutes or longer. More preferably, it is 6 minutes or more and 10 minutes or less.

  In the present embodiment, in order to extend the residence time, for example, a method of reducing the supply amount of the alloy powder as compared with the conventional method can be adopted.

  In the process of finely pulverizing the alloy powder, ultrafine particles having an R-rich composition (R-rich ultrafine particles) are generated. Here, the R-rich ultrafine particles contain a large amount of rare earth elements such as Nd, Pr, Dy, and Tb.

  In the airflow pulverization method using the swirl flow pulverizer, the R-rich ultrafine particles are not separated and recovered at an early stage, but swirl in the pulverization tank together with the alloy powder in the pulverization tank. By rotating the R-rich ultrafine particles together with the alloy powder in the grinding tank, the R-rich ultrafine particles adhere to the alloy powder, and the surface of the particles is at least one kind of rare earth of Nd, Pr, Dy, Tb. It is considered that an RTB-based alloy powder covered with an R enriched layer containing an element is obtained.

  On the other hand, in other forms of jet mills other than the swirl type, the R-rich ultrafine particles are likely to be discharged from the pulverization tank at an early stage.

  The particle size of the alloy powder recovered after the fine pulverization step is, for example, 1.0 μm or more and 5.5 μm or less in D50 (powder particle size obtained by airflow dispersion type laser diffraction method, volume reference central value). . In order to further improve the magnetic properties in this embodiment, the particle size is preferably D50 to 2.5 μm to 5.0 μm, more preferably 3.14 μm to 4.93 μm.

  Hereinafter, details of an exemplary swirling flow type crusher used in the present embodiment will be described.

  FIG. 3A is a schematic diagram showing the swirling flow crusher 1. FIG. 3B shows a cross section taken along the line ZZ ′ of FIG. The swirl type pulverizer 1 includes a pulverization tank 2A that accommodates pulverized gas and pulverized powder that are swirled therein. Here, the crushing tank 2 </ b> A is a space surrounded by the housing 2.

  The housing 2 is provided with a plurality of pulverized gas introduction nozzles 5 communicating with the pulverization tank 2A. Each of the pulverized gas introduction nozzles 5 is fixedly installed with its injection port directed toward the inside of the pulverization tank 2A (in the direction away from the center).

  As shown in FIGS. 3A and 3B, one of the pulverized gas introduction nozzles 5 is provided with a coarsely pulverized powder supply port 3 for supplying the coarsely pulverized alloy powder into the pulverization tank. . From the coarsely pulverized powder supply port 3, the alloy powder supplied from the hopper-like coarsely pulverized powder supply unit 4 is supplied into the pulverized gas, and in the pulverization tank 2 A together with the high-speed pulverized gas injected from the pulverized gas introduction nozzle 5. Will be injected and introduced.

  High-pressure gas (crushed gas) is fed into the pulverized gas introduction nozzle 5 from a high-pressure gas supply device (not shown) through an air feed tube.

  In the present embodiment, the high-pressure gas supply device is configured so that the pressure of the pulverized gas supplied to the pulverization tank 2A can be set to 0.75 MPa or more as a gauge pressure.

  The alloy powder introduced into the pulverization tank 2A is entrained in the high-speed swirl flow 18 generated by the gas ejected from the plurality of pulverization gas introduction nozzles 5 disposed along the inner wall, and swirls in the pulverization tank 2A. To do. At this time, collision and grinding occur, and in the process, R-rich ultrafine particles generated during the collision and grinding adhere to the particles of the alloy powder.

  By staying in the pulverization tank 2A in the swirling flow pulverizer 1 for a predetermined time, an RTB-based alloy powder in which the surface of the alloy powder particles is covered with an R concentrated layer is obtained. In this way, the RTB-based alloy powder whose surface is covered with the R-enriched layer, when the retention amount in the pulverization tank exceeds a certain level, the finely pulverized powder discharged above the central portion of the pulverization tank 2A. It is taken out from the outlet 6.

  In the configuration shown in FIGS. 3A and 3B, the amount of the alloy powder that can stay in the pulverization tank 2A is determined for each apparatus and for each operating condition. When the amount of the alloy powder exceeding the amount is introduced into the pulverizing tank 2A, the alloy powder corresponding to the introduced amount is discharged out of the tank. For this reason, the residence time in a crushing tank can be adjusted by adjusting the introduction amount to the crushing tank 2A.

[Method for producing RTB-based sintered magnet]
[Orientation of main phase crystals by external magnetic field]
In the case of manufacturing an anisotropic sintered magnet, the RTB-based alloy powder is crystallized in the main phase by an external magnetic field.

  More specifically, in order to orient the main phase crystal by an external magnetic field, it may be performed by a mold press having a magnetic field application coil, or after filling the filling container with powder at high density, It may be oriented. Do not exclude other methods.

  The applied magnetic field may be a static magnetic field or a pulsed magnetic field.

[Molding]
When using a die press, the density of the compact is preferably 3.7 g / cm ³ or more and 4.7 g / cm ³ or less. When adjusted to this range, the molded body tends to increase the degree of orientation while maintaining the strength of the molded body. If it is less than 3.7 g / cm ³ , the strength of the molded product is insufficient when it is performed by a mold press, and there is a risk of cracking during handling of the molded product. If it exceeds 4.7 g / cm ³ , the strength of the molded product increases, but the movement of the particles is suppressed during pressurization by pressing, and the degree of orientation may not be increased.

  It is desirable to minimize the use of a lubricant or the like in order to suppress carbon uptake when producing a molded body of the above-described RTB-based alloy powder by a die press or an isostatic press. In the sintering process (or the previous process), a highly volatile lubricant is selected in order to enable degreasing.

  With the RTB-based alloy powder according to the embodiment of the present invention, high orientation can be obtained even if the amount of lubricant used is reduced or no lubricant is used.

  In the mold press, the pressure applied at the time of molding is not particularly limited, but is, for example, 9.8 MPa or more, more preferably 19.6 MPa or more, and 245 MPa or less, more preferably 147 MPa or less.

[Sintering]
The sintering step is preferably performed in a sintering furnace maintained in a vacuum or an inert gas atmosphere at atmospheric pressure or lower. The inert gas here refers to Ar or He gas. As a method of maintaining an inert gas atmosphere at atmospheric pressure or lower, a method of introducing a small amount of inert gas into a sintering furnace while performing evacuation by a vacuum pump is preferable. In this case, evacuation may be performed intermittently or inert gas may be introduced intermittently. Also, both evacuation and introduction can be performed intermittently.

  Sintering is usually performed by holding the compact in a temperature range of 950 ° C. to 1100 ° C. for 30 minutes to 16 hours. Sintering may be performed in multiple steps at the same temperature or different temperatures. Conditions for cooling after sintering can be appropriately combined so that the value of the coercive force of the obtained magnet becomes a target value including the following heat treatment.

  In addition to the sintering method described above, any sintering means used in the powder metallurgy method such as a hot press for heating while applying pressure from the outside and an electric current sintering for heating the compact by Joule heat can be applied. When these methods are used, the sintering temperature and time are not limited to the above.

After the sintering, the density of the magnet obtained as a sintered body is preferably 7.3 g / cm ³ or more. More preferably, it is 7.5 g / cm ³ or more.

When the RTB-based alloy powder having the R-enriched layer is sintered, the dispersibility of Nd, Pr, Dy, and Tb is improved, and a uniform R-rich phase is formed at the crystal grain boundary. As a result, the coercive force H _{cJ of the RTB} -based sintered magnet produced using this alloy powder is improved.

[Heat treatment]
For the purpose of increasing the coercive force, heat treatment can be performed at a sintering temperature or lower after the end of sintering. Further, this heat treatment may be performed a plurality of times at the same temperature or at different temperatures. Various conditions can be selected for the cooling conditions during the heat treatment in accordance with the target coercive force value.

  In addition, when sufficient coercive force is obtained in the state after sintering, it is not necessary to perform heat treatment.

[processing]
The magnet obtained as a sintered body may have a shape close to that of the final product, but it may not be the case. Generally, R after sintering is obtained by machining such as cutting, grinding, and polishing. -Finish the T-B sintered magnet into a predetermined shape. In addition, as long as this process is after sintering, you may perform before or after heat processing, or in the middle of several heat processing.

[surface treatment]
In order to prevent rust, it is preferable to subject the obtained RTB-based sintered magnet to a surface coating treatment. Examples of the surface coating treatment include Ni plating, Sn plating, Zn plating, Al deposition, Al alloy deposition, and resin coating.

  Examples of the present invention will be described below.

Example 1
Nd, electrolytic iron, and low carbon ferroboron alloy with a purity of 99.5% or more are used as main raw materials, and additive elements (Co and M) are added as pure metals or alloys with Fe, and finally the R-T-B system The composition of the alloy powder and sintered magnet is Nd: 30.5, B: 0.94, Co: 0.9, Cu: 0.1, Al: 0.1, Ga: 0.1, Fe: balance [mass %] Was rapidly cooled by a strip casting method to obtain a plate-like alloy having a thickness of 0.1 to 0.3 mm.

  The alloy was held in a hydrogen pressure atmosphere using a heat treatment furnace capable of pressurization, heated to 600 ° C. in a vacuum, and then cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 μm or less.

  Next, using the swirl type pulverizer 1 shown in FIGS. 3 (a) and 3 (b), the supply amount and the residence time are changed, and the pulverization conditions for finely pulverizing the alloy powder and the particle size of the obtained powder ( D50) is shown in Table 1.

The volume of the crushing tank of the apparatus used in this example is 314 cm ³ . Here, the pulverized gas is N ₂ gas whose oxygen concentration is controlled to 8000 ppm or less. The pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.

  The supply amount is the amount of alloy powder charged into the grinding tank per minute. The residence time is the time required from the start of supply from the coarsely pulverized powder supply nozzle to the presence of the alloy powder in the recovery container (not shown) through a cyclone (not shown). Even if it is a small amount, it can be recovered after 4 minutes, and when it is recovered after 4 minutes and 4 minutes, it is 6 minutes.

  Surface analysis was performed on Sample 1 (Example) and Sample 2 (Comparative Example) in Table 1 above. The result is shown in FIG.

  FIGS. 1C and 1D show the results of element mapping by AES (Auger Electron Spectroscopy) on the surface of the alloy powders of Sample 1 and Sample 2. FIG. Element information (here, Nd) in the surface layer of the alloy powder is indicated by the density of the black and white density. A region shown in white is a region having a high Nd concentration, and a region shown in black is a region having a low Nd concentration.

  As can be seen from FIG. 1C, the surface of the sample 1 has many high-luminance regions with high Nd concentration, and it can be confirmed that Nd is widely distributed on the surface of the particles.

  On the other hand, as can be seen from FIG. 1 (d), Nd is locally unevenly distributed on the surface of the sample 2.

  Next, AES depth profile was analyzed. FIG. 2 shows the AES depth profile from the surface of the alloy powder particles of Sample 1 to the inside. The analysis value is an average value in a region of 1 μm × 1 μm, and the analysis was performed while digging the finely pulverized alloy powder in the depth direction at a constant speed with a sputtering rate of 3.8 nm / min by Ar as a target value.

  At the right end of FIG. 2, the depth profiles of Fe, Nd, B, and O are shown from the top.

As can be seen from FIG. 2, the R ₂ Fe ₁₄ B phase has a substantially constant concentration of Fe, B, and Nd, and the R enriched layer extends from there to the left end of the graph of FIG. In Sample 1, an R enriched layer is formed in the vicinity of the surface of the particles, and the inside of the R enriched layer is composed of an R ₂ Fe ₁₄ B phase. The R enriched layer contains Nd as a rare earth element. A region having an Nd concentration of 20 atomic% to 32 atomic% formed on the particle surface can be regarded as an R concentrated layer, and in the example shown in FIG. 2, the thickness of the R concentrated layer can be estimated to be about 50 nm. .

  The oxygen content of the particles uniformly decreased from the particle surface toward the inside in the R concentrated layer. Here, “decreases uniformly” in this specification means that the oxygen concentration gradually decreases continuously from the particle surface toward the inside as shown in FIG. However, a region where the concentration of oxygen is constant or a region where the concentration of oxygen slightly increases may be included in the direction from the surface of the powder to the inside.

  Since the RTB-based alloy powder of the example is manufactured by the fine pulverization process as described above, the alloy powder after the coarse pulverization is not exposed to the outside air, and the R-rich ultrafine particles adhere to it. Conceivable.

The R concentrated layer contained Fe and B in addition. The R enriched layer is formed by adhering R-rich ultrafine particles generated in the process of pulverizing the alloy powder to the R ₂ Fe ₁₄ B phase. include.

The concentrations of Fe and B in the R concentrated layer were lower than the concentrations of Fe and B in the R ₂ Fe ₁₄ B phase formed inside (inside the particles) of the R concentrated layer.

  In FIG. 1 (a), five locations where the contrast was dark were selected and those regions were analyzed anew. As a result, it was confirmed that Nd was widely distributed on the surface of the particles. Thus, it was found that the surfaces of the particles of Sample 1 were entirely covered with the Nd-rich layer, including the part that was not visible at first glance. On the other hand, in Sample 2, even if an Nd-rich portion was present, it remained on the particle surface, and it was confirmed that the Nd-rich layer did not cover the powder.

  The R-enriched layer at an arbitrary position of 10 particles randomly extracted from the alloy powder of Sample 1 was measured and found to be in the range of 30 nm to 90 nm.

  After mixing 0.16% by mass of methyl caprylate with the alloy powder of the example (sample 1) and the comparative example alloy powder (sample 2), the magnetic field application direction and the pressing direction in a magnetic field of 1.36 MA / m Were molded at the molding pressure of 49 MPa under the conditions of the orthogonal pressure of Sample 1 (Example) and Sample 2 (Comparative Example) shown in Table 2 below.

  Samples 1 and 2 were sintered in a reduced pressure Ar gas atmosphere at 1080 ° C. for 4 hours. Further, the obtained RTB-based sintered magnet was heat-treated at 500 ° C. for 2 hours in a vacuum atmosphere, and then cooled.

These samples, after machining, was measured coercivity H _cJ and remanence B _r of at room temperature B-H tracer. The results are shown in Table 2.

As shown in Table 2, Sample 1 (Example) has the same composition as Sample 2 (Comparative Example), but has an improved H _cJ value.

This is because the R-rich layer enriched with Nd on the surface of the particles increases the dispersibility of the R-rich phase in the sintered body produced using it, and the grain boundaries of the sintered body are optimized. This is considered to be because H _cJ became higher.

For the case of a general material of the same powder, H _cJ is improved by reducing the degree of orientation, but B _r is decreased, the sample 1 is B _r as compared to the sample 2 is not reduced, It is reasonable to consider that the improvement in H _cJ is not due to a decrease in the degree of orientation but due to the dispersibility of the R-rich phase.

(Example 2)
Nd, Pr, Dy, Tb having a purity of 99.5% or more, electrolytic iron, and a low carbon ferroboron alloy are used as main raw materials, and additive element M is added as a pure metal or an alloy with Fe. The composition of the B-based alloy powder and the sintered magnet is Nd: 22.8, Pr: 7.6, Dy: 1.0, Tb: 1.0, B: 1.05, Cu: 0.1, Al: 0 .3, Nb: 0.5, Fe: The molten alloy melted to the balance [mass%] was quenched by a strip casting method to obtain a plate-like alloy having a thickness of 0.1 to 0.3 mm.

  This alloy was held in a hydrogen pressure atmosphere using a heat treatment furnace capable of pressurization, heated to 660 ° C. in a vacuum, and then cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 μm or less.

  Next, using the swirling flow type pulverizer 1 shown in FIGS. 3 (a) and 3 (b), the supply amount and the residence time were changed, and the pulverization conditions for finely pulverizing the alloy powder and the particle size of the obtained powder were determined. Table 3 shows.

The volume of the crushing tank of the apparatus used in this example is 314 cm ³ . Here, the pulverized gas is N ₂ gas whose oxygen concentration is controlled to 8000 ppm or less. The pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.

  As will be described later, in Sample 3, an R-enriched layer was formed on the particle surface, whereas in Sample 4, an R-enriched layer was not formed on the particle surface and a region with a high R concentration was present locally. I just did.

Example 3
Nd, Pr, electrolytic iron, low carbon ferroboron alloy having a purity of 99.5% or more is used as a main raw material, and additive elements (Co and M) are added as pure metal or an alloy with Fe. The composition of the B-based alloy powder and the sintered magnet is Nd: 21.9, Pr: 7.3, B: 0.94, Co: 2.0, Cu: 0.1, Al: 0.05, Ga: 0 .1, Fe: The molten alloy melted so as to be the balance [mass%] was rapidly cooled by a strip cast method to obtain a plate-shaped alloy having a thickness of 0.1 to 0.3 mm.

  The alloy was held in a hydrogen pressure atmosphere using a heat treatment furnace capable of being pressurized, heated to 580 ° C. in a vacuum, and then cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 μm or less.

  Next, using the swirling flow type pulverizer 1 shown in FIGS. 3 (a) and 3 (b), the supply amount and the residence time were changed, and the pulverization conditions for finely pulverizing the alloy powder and the particle size of the obtained powder were determined. Table 4 shows.

The volume of the grinding tank of the apparatus used in this example is 628 cm ³ . Here, the grinding gas is helium gas. The pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.

  As will be described later, in Sample 5, the R concentrated layer was formed on the particle surface, whereas in Sample 6, the R concentrated layer was not formed on the particle surface, and there was a region with a high R concentration. I just did.

(Example 4)
Nd, Pr, Dy, Tb, purity 99.5% or more of Nd, Pr, Tb, electrolytic iron, and low carbon ferroboron alloy are used as main raw materials, and additive elements (Co and M) are added as pure metal or an alloy with Fe. The composition of the RTB-based alloy powder and the sintered magnet is Nd: 22.5, Pr: 7.5, Dy: 0.1, Tb: 0.1, B: 0.90, Co: 0.9 , Cu: 0.15, Al: 0.1, Ga: 0.5, Zr: 0.1, Fe: The molten alloy melted so as to be the balance [mass%] was quenched by a strip cast method to obtain a thickness. A plate-shaped alloy of 0.1 to 0.3 mm was obtained.

  The alloy was held in a hydrogen pressure atmosphere using a heat treatment furnace capable of being pressurized, heated to 550 ° C. in a vacuum, and then cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 μm or less.

  Next, using the swirling flow type pulverizer 1 shown in FIGS. 3 (a) and 3 (b), the supply amount and the residence time were changed, and the pulverization conditions for finely pulverizing the alloy powder and the particle size of the obtained powder were determined. Table 5 shows.

The volume of the crushing tank of the apparatus used in this example is 314 cm ³ . Here, the grinding gas is argon gas. The pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.

  As will be described later, in Sample 7, the R concentrated layer was formed on the particle surface, whereas in Sample 8, the R concentrated layer was not formed on the particle surface, and there was a region with a high R concentration. I just did.

(A more detailed analysis result about Examples 2-4)
Hereinafter, a more detailed analysis result is demonstrated about each sample demonstrated in said Examples 2-4.

  For the alloy powders of Samples 3, 5, 7 (Examples) and Samples 4, 6, 8 (Comparative Examples) shown in Table 3, Table 4, and Table 5, AES (Auger Electron Spectroscopy: Elemental mapping by Auger electron spectroscopy) was conducted and the presence or absence of an R-enriched layer on the surface was examined. The results were as shown in Table 6 below.

  Samples 3, 5, and 7 (Examples) had an R enriched layer having an R concentration of 20 atomic% to 32 atomic%, and the R concentrated layer was widely distributed on the particle surface. A tendency similar to that of Sample 1 of Example 1 was confirmed.

  Samples 4, 6, and 8 (comparative examples) do not have an R-enriched layer having an R concentration of 20 to 32 atom%, and remain attached to the particle surface even if Nd-rich portions exist. The Nd-rich layer was not covering the powder. A tendency similar to that of Sample 2 of Example 1 was confirmed.

  Further, samples 3, 5, and 7 (Examples) were analyzed for the depth profile of AES. When the oxygen content of the particles and the presence or absence of Fe and B were examined, the results were as shown in Table 7 below. Samples 3, 5, and 7 (Examples) confirmed the same tendency as Sample 1 of Example 1.

  Next, 0.16 mass% of methyl caprylate was mixed with the alloy powder of the example (samples 3, 5, and 7) and the alloy powder of the comparative example (samples 4, 6, and 8), and then 1.36 MA / m. Molded bodies of Samples 3, 5, and 7 (Examples) and Samples 4, 6, and 8 (Comparative Examples) shown in Table 4 below were produced under the condition that the magnetic field application direction and the pressing direction were orthogonal to each other in a magnetic field.

  Samples 3 to 8 were sintered in a reduced pressure Ar gas atmosphere. Further, the obtained RTB-based sintered magnet was heat-treated at 500 ° C. for 2 hours in a vacuum atmosphere, and then cooled.

These samples, after machining, was measured coercivity H _cJ and remanence B _r of at room temperature B-H tracer. The results are shown in Table 8.

As shown in Table 8, Sample 3 (Example) has the same composition as Sample 4 (Comparative Example), but has an improved H _cJ value. Similarly, the comparison between Sample 5 (Example) and Sample 6 (Comparative Example), and the comparison between Sample 7 (Example) and Sample 8 (Comparative Example) have the same composition, but the H _cJ value is improved. doing.

This is because the alloy powders of Samples 3, 5, and 7 have the R-enriched layer on the surface of the particles as in Example 1, and therefore the dispersibility of the R-rich phase in the sintered body made using the same. This is thought to be because _HcJ was increased because the grain boundary of the sintered body was optimized.

Any samples 3,5,7, since B _r and comparative sample 4, 6 and 8 respectively are not reduced, the improvement of H _cJ is not due to the degree of orientation decreases, probably due to the dispersibility of the R-rich phase It is done.

  As described above, in the case of using the swirling flow type pulverizer, for example, the gauge pressure of the pulverization gas introduced into the pulverization layer is set to 0.75 MPa or more, and the residence time of the alloy powder in the pulverization layer is set. By setting it for 5 minutes or more, an alloy powder in which an R concentrated layer is widely formed over the entire surface of the particles can be obtained. Moreover, the coercive force can be improved by producing an RTB-based sintered magnet using the alloy powder in which the R concentrated layer is formed.

In the above embodiment, although the volume of the grinding chamber has been described with respect to the case of 314cm ^3, 628cm ^3, the size of the volume is not particularly limited. By appropriately adjusting the supply amount of the alloy powder according to the size of the volume, an alloy powder in which the R concentrated layer is formed over the entire surface can be obtained.

  The RTB-based alloy powder according to the embodiment of the present invention is suitably used for producing an RTB-based sintered magnet.

DESCRIPTION OF SYMBOLS 1 Swirling flow type pulverizer 2 Housing 2A Grinding tank 3 Coarse pulverized powder supply port 4 Coarse pulverized powder supply part 5 Grinding gas introduction nozzle 6 Finely pulverized powder discharge port 18 High-speed swirl flow

Claims (2)

The surface of the particle is covered with an R enriched layer containing at least one rare earth element of Nd, Pr, Dy, and Tb, and the rare earth element in the R enriched layer is 20 atomic% or more and 32 atomic% or less. range near is,
An R ₂ Fe ₁₄ B phase exists as a main phase in an inner region surrounded by the R enriched layer of the particles ,
The R enriched layer is composed of a plurality of R-rich fine particles attached to the surface of the particles, and the thickness of the R enriched layer is 30 nm or more and 90 nm or less,
Oxygen concentration in the thickness direction of the R concentration layer, Ri Contact decreases uniformly towards the inside from the particle surface,
The R enriched layer further contains Fe and B,
The concentration of Fe in the R enriched layer is lower than the concentration of Fe in the R ₂ Fe ₁₄ B phase inside the R enriched layer ,
The concentration of B in the R enriched layer is lower than the concentration of B in the R ₂ Fe ₁₄ B phase inside the R enriched layer . An RTB-based sintered magnet obtained by sintering using the RTB-based alloy powder according to claim 1 to obtain a sintered body.