Auxiliary alloy powder and method for producing auxiliary alloy powder

Abstract

Auxiliary alloy powder according to the present invention has a group 2 element content of 20-90 atomic% inclusive, has the average particle diameter of 0.1-30 μm inclusive, and has a melting endothermic peak that is observed at 620°C or lower in differential scanning calorimetry.

Description

Auxiliary alloy powder and method for producing auxiliary alloy powder

[0001] The present disclosure relates to auxiliary alloy powders for rare earth iron-based sintered magnets.

[0002] In recent years, Sm (samarium)-Fe (iron)-N (nitrogen) magnets have been developed as high-performance magnets. Sm-Fe-N compounds are known to have both high spontaneous magnetization and high anisotropy magnetic fields, as well as high heat resistance. However, because Sm-Fe-N compounds tend to thermally decompose at temperatures around 620°C, powder of magnetic material containing Sm-Fe-N compounds cannot be heated above the decomposition temperature when obtaining a compact. For this reason, when molding sintered magnets using powder of Sm-Fe-N compounds, methods using alloy powder as a sintering aid to promote densification have been investigated.

[0003] As a method for producing alloy powder, for example, Non-Patent Document 1 discloses a technique for producing alloy powder containing Mg or Ca by air atomization.

[0004] Investigations of Manufacturing of Magnesium Alloy Powder by Air Atomization (J. Jpn. Soc. Powder Metallurgy, 66 (2019) 485-492)

[0005] However, with the technology described in Non-Patent Document 1, when the alloy is powdered, it reacts with oxygen in the air, causing an oxidation reaction. In addition, the powder produced by the air atomization method has a particle size of several tens of micrometers or more, which means that the density of the Sm-Fe-N sintered magnet cannot be sufficiently obtained. 17 The present invention is not limited to Sm-Fe-N sintered magnets with a TbCu7 structure or ThMn 12 This is a common problem with rare earth iron-based sintered magnets containing Sm that have a structure similar to that of the magnet.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a technique for improving the sinterability of rare earth iron-based sintered magnets.

[0007] The present disclosure has been made to solve at least one of the above-mentioned problems, and can be realized in the following forms.

[0008] <1> One aspect of the present disclosure provides an auxiliary alloy powder for a rare earth iron-based sintered magnet, which has a Group 2 element content of 20 atomic % or more and 90 atomic % or less, an average particle size of 0.1 μm or more and 30 μm or less, and exhibits a melting endothermic peak at 620°C or less in differential scanning calorimetry.

[0009] According to this type of auxiliary alloy powder, the Group 2 element content of 20 atomic % to 90 atomic % is suitable for ensuring the sinterability of the rare earth iron-based sintered magnet, and the average particle size of 0.1 μm to 30 μm can improve the sinterability of the rare earth iron-based sintered magnet. Furthermore, by containing 20 atomic % to 90 atomic % of the Group 2 element and selecting the remaining metal elements so that the melting point is 620°C or lower (an endothermic peak is observed below 620°C in differential scanning calorimetry), sintering at temperatures below the thermal decomposition temperature of the rare earth iron-based sintered magnet becomes possible.

[0010] <2> In the auxiliary alloy powder of the above embodiment, the oxygen content may be 10% by mass or less. Group 2 elements have a high affinity for oxygen and tend to bond with surrounding oxygen to form oxides. When these metal oxides form, the melting point may increase. According to this auxiliary alloy powder, the oxygen content is 10% by mass or less, thereby suppressing the increase in the melting point.

[0011] <3> The auxiliary alloy powder of the above form may have a nitrogen content of 1% by mass or more and 10% by mass or less, which can suppress the nitriding reaction on the alloy surface and the rise in the melting point, and also can obtain a fine powder by including nitrogen in the alloy.

[0012] <4> The auxiliary alloy powder of the above form may have an average particle size of 0.1 μm or more and 10 μm or less, which further improves the dispersibility of the auxiliary in the rare earth iron-based sintered magnet and further increases the density of the sintered body.

[0013] <5> According to one aspect of the present disclosure, there is provided an auxiliary alloy powder for a rare earth iron-based sintered magnet, the auxiliary alloy powder having a Group 2 element content of 20 atomic % or more and 90 atomic % or less, an average particle size of 0.01 μm or more and 0.1 μm or less, and a melting endothermic peak observed at 620°C or less in differential scanning calorimetry.

[0014] This type of auxiliary alloy powder for rare earth iron-based sintered magnets has a finer powder with an average particle size of 0.01 μm or more and 0.1 μm or less, which improves the dispersibility of the auxiliary alloy powder and allows the auxiliary alloy powder to be dispersed more uniformly in the magnetic powder, thereby further improving the density of the Sm—Fe—N based magnet.

[0015] <6> According to another aspect of the present disclosure, there is provided a method for producing an auxiliary alloy powder. This method includes a step of producing the auxiliary alloy powder from an alloy ingot containing 20 atomic % to 90 atomic % of a Group 2 element in a low-oxygen atmosphere. This reduces the amount of oxygen in the alloy. The above step includes, for example, a step of mechanically pulverizing the alloy ingot, a step of producing powder by gas atomization, a thermal plasma method, or a combination thereof.

[0016] The present disclosure can be realized in various forms, for example, in the form of a rare earth iron-based sintered magnet, a permanent magnet for a motor, a method for manufacturing a rare earth iron-based sintered magnet, etc.

[0017] Fig. 1 is a process diagram showing an example of a method for manufacturing auxiliary gun metal powder; Fig. 2 is an explanatory diagram conceptually showing the cross-sectional structure of a sintered magnet; Fig. 3 is a process diagram showing an example of a method for manufacturing a sintered magnet; Fig. 4 is a diagram showing evaluation results of samples; Fig. 5 is an explanatory diagram of a sample for SEM observation; Fig. 6 is a diagram showing evaluation results of samples; Fig. 7 is a diagram showing the results of wettability evaluation of an alloy;

[0018] <Embodiment> The auxiliary alloy powder of this embodiment is for rare earth iron-based sintered magnets. The rare earth iron-based sintered magnet is Th2Zn 17 type structure, TbCu7 type structure, and ThMn 12 Examples include those having a mold structure.

[0019] The auxiliary alloy powder of this embodiment contains 20 atomic % or more and 90 atomic % or less of Group 2 elements, which are elements belonging to Group 2 of the periodic table and include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0020] In addition to the Group 2 element, the auxiliary alloy powder contains, for example, silver (Ag), aluminum (Al), copper (Cu), zinc (Zn), etc. The auxiliary alloy powder contains 20 atomic % to 90 atomic % of the Group 2 element, and by selecting the remaining metal elements, the melting point is set to 620°C or lower (an endothermic peak is observed at 620°C or lower in differential scanning calorimetry). This makes it possible to sinter the rare earth iron-based sintered magnet at or below the thermal decomposition temperature, thereby improving the sintered density of the rare earth iron-based sintered magnet.

[0021] For example, Sm (samarium)-Fe (iron)-N (nitrogen) magnets are subject to sintering temperature restrictions because they undergo thermal decomposition at temperatures above 620°C, making it impossible to obtain high-density sintered bodies in the past. In contrast, when the auxiliary alloy powder of this embodiment is used, the melting point is 620°C or lower, a temperature at which the main phase does not decompose. Therefore, when producing a sintered magnet, the main phase does not decompose even when heated at a temperature at which the alloy melts. Therefore, by using the auxiliary alloy powder of this embodiment, liquid phase sintering can occur, and SmFe 17 N3 / Sm2Fe 17 A second phase consisting of the auxiliary alloy powder can be formed as a grain boundary phase at the interface of N3.

[0022] The melting point of the auxiliary alloy powder can be measured using a differential scanning calorimeter (DSC). A 10-20 mg sample of liquid-quenched foil obtained by a known melt spinning method is weighed out and used as the measurement sample. A BN (boron nitride) pan is used for the measurement, with the measurement temperature range from room temperature to 700°C and the heating rate at 10°C / min. The melting point is determined using the peak melting temperature that appears within the measurement temperature range.

[0023] The auxiliary alloy powder has an average particle size of 0.1 μm or more and 30 μm or less, more preferably 0.1 μm or more and 10 μm or less. The particle size distribution is measured using a dry particle size distribution measuring device, and the resulting D50 is taken as the average particle size. When the auxiliary alloy powder has an average particle size of this order, the dispersion of the auxiliary in the rare earth iron-based sintered magnet is improved, thereby increasing the area (volume) over which the auxiliary acts on the rare earth iron-based magnet powder and improving the sinterability of the rare earth iron-based sintered magnet.

[0024] The auxiliary alloy powder may have an average particle size of 0.01 μm or more and 0.1 μm or less. By making the auxiliary alloy powder finer, the dispersibility of the auxiliary alloy powder can be improved, and the auxiliary alloy powder can be dispersed more uniformly in the magnetic powder. Use of such an auxiliary alloy powder can further improve the density of the rare earth iron-based sintered magnet.

[0025] The oxygen content of the auxiliary alloy powder is not particularly limited, but is preferably 10% by mass or less. Group 2 elements have a high affinity for oxygen and tend to bond with surrounding oxygen to form oxides. When Group 2 elements become metal oxides, there is a risk of the melting point increasing. By setting the oxygen content of the auxiliary alloy powder to 10% by mass or less, the increase in melting point can be suppressed, and the auxiliary alloy powder can function as a low-melting-point auxiliary.

[0026] The nitrogen content of the auxiliary alloy powder is not particularly limited, but is preferably 1% by mass or more and 10% by mass or less, and more preferably 4% by mass or more and 10% by mass or less. By including nitrogen in the alloy, finer powder can be obtained. However, if the nitrogen content is too high, the nitriding reaction on the alloy surface becomes significant, and the melting point rises significantly due to the formation of surface nitrides. By setting the nitrogen content to 10% by mass or less, the nitriding reaction on the alloy surface is suppressed, thereby suppressing the rise in the melting point and making the melting point of the auxiliary alloy powder an appropriate temperature of 620°C or less.

[0027] An example of a method for incorporating nitrogen into an alloy is to perform pulverization in an organic solvent containing nitrogen (N) in its molecules, such as acetonitrile, in the pulverization step described below. Methods for controlling the amount of nitrogen in the alloy include adjusting pulverization conditions, such as the pulverization time and the rotation speed of the pulverizer (grinder, ball mill, etc.) in the pulverization step described below.

[0028] The auxiliary alloy powder may contain unavoidable impurity elements, etc., to the extent that the properties are not impaired. The unavoidable impurity elements refer to impurity elements whose inclusion cannot be avoided when producing the auxiliary alloy powder of the embodiment, or whose avoidance would result in a significant increase in production costs. Examples of such unavoidable impurity elements include impurity elements in raw materials.

[0029] As described above, the auxiliary alloy powder of this embodiment contains the Group 2 element in the above-described content and has the above-described average particle size and melting point, thereby improving dispersibility in the rare earth-iron-based sintered magnet and enabling the sintered density of the rare earth-iron-based sintered magnet to be improved.

[0030] 1 is a process diagram showing an example of a method for producing an auxiliary alloy powder according to an embodiment. The method for producing the auxiliary alloy powder according to this embodiment is not particularly limited, but can be, for example, the method described below. In addition to the methods described below, the auxiliary alloy powder may also be produced using, for example, a gas atomization method or a thermal plasma method. As shown in FIG. 1 , the method for producing the auxiliary alloy powder involves the steps of an alloy ingot production step P21, a pulverization step P22, a drying step P23, and a classification step P24, in this order.

[0031] In the alloy ingot production process P21, multiple granular metal raw materials containing Group 2 elements are weighed so that the content of Group 2 elements is 20 atomic weight % or more and 90 atomic weight % or less, and are melted under reduced pressure in an inert gas (e.g., Ar) using an arc melting furnace to produce an alloy ingot.

[0032] In the pulverization step P22, the alloy ingot produced in the alloy ingot production step P21 is pulverized in a low-oxygen atmosphere. The pulverization is performed using, for example, a grinder, a planetary ball mill, or the like. The oxygen concentration is adjusted by controlling the atmosphere in the pulverization step. A low oxygen concentration is a concentration lower than the oxygen concentration in the atmosphere (approximately 21 vol%). The oxygen concentration is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 0.5 ppm or less. For example, a low-oxygen atmosphere can be achieved by injecting an inert gas into a vacuum chamber. By performing the pulverization step in a low-oxygen atmosphere, oxidation of the Group 2 elements can be suppressed, and an increase in the melting point of the auxiliary alloy powder can be suppressed.

[0033] In the drying step P23, the slurry obtained in the pulverization step P22 is vacuum-dried. In the classification step P24, the alloy powder dried in the drying step P23 is classified using a sieve to obtain auxiliary alloy powder 22 having an average particle size of 0.1 μm or more and 30 μm or less. Furthermore, by selecting the sieve opening, auxiliary alloy powder having an average particle size of 0.01 μm or more and 0.1 μm or less can also be obtained. It is preferable to perform the alloy ingot preparation step P21, pulverization step P22, drying step P23, and classification step P24 in a low-oxygen concentration atmosphere, since this can suppress oxidation of the auxiliary alloy powder. Even when preparing auxiliary alloy powder from an alloy ingot using at least one of a gas atomization method and a thermal plasma method, performing the process in a low-oxygen concentration atmosphere is also preferable, since this can suppress oxidation of the auxiliary alloy powder.

[0034] The rare earth iron-based sintered magnet manufactured by adding the auxiliary alloy powder of this embodiment will be described below. FIG. 2 is an explanatory diagram conceptually showing the cross-sectional structure of a sintered magnet 100 manufactured by adding the auxiliary alloy powder of this embodiment. The sintered magnet 100 is a rare earth iron-based sintered magnet, and is composed of ThZn. 17 The alloy powder includes a first phase 10 having a main phase of Sm—Fe—N (samarium-iron-nitrogen) crystal grains having a morphology similar to that of the alloy powder of the present embodiment, and a second phase 20. As will be described later, the second phase 20 is formed by melting and then solidifying the auxiliary alloy powder 22 of the present embodiment.

[0035] 2, the first phase 10 is hatched with diagonal lines that slope upward to the right, and the second phase 20 is hatched with diagonal lines that slope downward to the right. As shown in the figure, the first phase 10 has a plurality of Sm—Fe—N crystal grains 10G. The second phase 20 is located at the grain boundaries between the Sm—Fe—N crystal grains 10G and the Sm—Fe—N crystal grains 10G. The sintered magnet 100 may have voids V at the grain boundaries between the Sm—Fe—N crystal grains 10G and the Sm—Fe—N crystal grains 10G.

[0036] The main phase, Sm-Fe-N crystal grains 10G, is composed of Th2Zn 17 SmFe with type structure 17 N3. Sintered magnet 100 exhibits magnetism through Sm—Fe—N crystal grains 10G (main phase). The crystal structure of the main phase can be identified by, for example, subjecting sintered magnet 100 to X-ray diffraction analysis. The main phase refers to the compound that determines the properties of the sintered magnet.

[0037] SmFe 17 Since N3 has excellent saturation magnetization and a large anisotropic magnetic field, it can withstand heat and a reverse magnetic field and generate a high magnetic field. 17 The phase may include a structure different from the main phase, such as a TbCu7 type structure, a TbCu7 type structure, etc. Here, Tb is terbium, and Cu is copper.

[0038] Fig. 3 is a process diagram showing an example of a method for manufacturing a sintered magnet 100. In the method for manufacturing a sintered magnet 100 shown in Fig. 3, steps are performed in the order of a sintered magnet powder manufacturing step P0 and a sintering step P4. In the sintered magnet powder manufacturing step P0, steps are performed in the order of a crushing step P1, an alloy powder manufacturing step P2, and a mixing step P3.

[0039] In the crushing step P1, Th2Zn 17 Coarse powder containing Sm—Fe—N single crystals having a crystalline structure is pulverized to obtain Sm—Fe—N crystal grains. 17The average particle size of the Sm—Fe—N crystal grains after pulverization is not particularly limited, but is preferably 0.1 μm to 20 μm, more preferably 0.4 μm to 10 μm, and even more preferably 1 μm to 5 μm.

[0040] In the alloy powder preparation step P2, the auxiliary alloy powder 22 of this embodiment is prepared as described above (FIG. 1).

[0041] In the mixing step P3, a sintered magnet powder is obtained as a mixed powder by dispersing the Sm—Fe—N crystal grains and the auxiliary alloy powder 22. The mixing step P3 may be a wet method in which the Sm—Fe—N crystal grains and the auxiliary alloy powder 22 are dispersed in a solvent (e.g., ethanol), or a dry method in which the Sm—Fe—N crystal grains and the auxiliary alloy powder 22 are dispersed in an inert gas (e.g., argon gas, helium gas, nitrogen gas, etc.).

[0042] The above-mentioned pulverization step P1, auxiliary alloy powder production step P2, and mixing step P3 are all performed in a low-oxygen atmosphere, which prevents oxidation of the Sm—Fe—N crystal grains and auxiliary alloy powder and ensures wettability between the Sm—Fe—N crystal grains and auxiliary alloy powder.

[0043] In the sintering step P4, the sintered magnet powder produced in the sintered magnet powder production step P0 is molded and pressure-sintered at a sintering temperature of 600°C or less in a low-oxygen atmosphere. In the sintering step P4, firing is performed in an atmosphere with an oxygen concentration similar to that of the crushing steps P1 to P3. By setting the sintering temperature to 600°C or less, thermal decomposition of the Sm—Fe—N crystal grains can be suppressed. Furthermore, by performing the sintering step P4 in a low-oxygen atmosphere, oxidation of the Sm—Fe—N crystal grains and auxiliary alloy powder can be suppressed. As a result, the density can be improved, and the magnetization of the sintered magnet 100 can be improved.

[0044] The sintered magnet produced as described above can be used as a permanent magnet for various motors, such as motors for EVs, motors built into robots, motors built into drones, and elevator motors.

[0045] The present disclosure will be explained in more detail using examples. Figure 4 shows the evaluation results for Samples 1 to 12. Sm—Fe—N sintered magnets were produced using Samples 1 to 12, which contained auxiliary alloy powders with different compositions, according to the manufacturing method described in the above embodiment (all samples were produced under the same conditions), and the densities of the sintered magnets were evaluated. In the examples, magnesium (Mg), calcium (Ca), and barium (Ba) were used as Group 2 elements. Note that Figure 4 shows the densities of Sample 13, an Sm—Fe—N sintered magnet produced without the addition of auxiliary alloy powder.

[0046] 1. Production of Samples (Auxiliary Alloy Powders) The auxiliary alloy powders of Samples 1 to 12 were produced by the production method (FIG. 1) exemplified in the above embodiment.

[0047] (1) Process P21 for Producing an Alloy Ingot Containing a Group 2 Element The following metals (granular metal raw materials) were used as the raw materials for the ingot: Ca metal (granular) Ba metal (granular) Mg metal (granular) Ag metal (granular) Cu metal (granular) Zn metal (granular) Al metal (granular) These granular metal raw materials were weighed out to have the composition ratios shown in Fig. 4, and melted in an arc melting furnace under reduced pressure of argon (Ar) to produce an alloy ingot.

[0048] (2) Milling Process P22: The alloy ingot produced in the alloy ingot production process P21 was first ground into chips using a grinder in a glove box controlled at an oxygen concentration of 0.5 ppm or less to obtain coarse alloy powder. 0.5 g of the coarse alloy powder was placed in a stainless steel pot, and stainless steel balls and acetonitrile or heptane as a solvent were added. The powder was then milled in a planetary ball mill at a rotation speed of 200 rpm for 6 hours. Acetonitrile is an example of an organic solvent containing nitrogen (N).

[0049] (3) Drying Step P23 After the pulverization step P22 was completed, the obtained slurry was dried under vacuum in the same glove box.

[0050] (4) Classification Step P24 After completion of the drying step P23, the mixture was sieved using a sieve with an opening of 63 μm, 40 μm or 20 μm to obtain auxiliary alloy powder.

[0051] 2. Evaluation Methods (1) Melting Point Measurement: Differential scanning calorimetry was performed on each alloy powder sample in a low-oxygen atmosphere in a glove box controlled at an oxygen concentration of 0.5 ppm or less. For the measurement, boron nitride (BN) pans were used for both the reference and sample sides. The measurement temperature range was 30°C to 700°C, and the heating rate was 10°C / min. Melting point analysis was performed on the curve obtained by the measurement from the extrapolated onset temperature (offset temperature) of the peak. (2) Oxygen and Nitrogen Content Analysis: The oxygen and nitrogen contents of each alloy powder sample were analyzed using an oxygen and nitrogen analyzer (EMGA-930: Horiba, Ltd.). To avoid exposure to the atmosphere during measurement, measurements were performed using alloy powders pre-encapsulated in Ni capsules in a glove box controlled at an oxygen concentration of 0.5 ppm or less. (3) Particle Size Distribution Measurement The particle size distribution of each sample was measured using a dry particle size distribution measurement device (HELOS & RODOS: Sympatec), and the obtained D50 was taken as the average particle size. (4) Sinterability Evaluation As shown below, each alloy powder sample was added to produce an Sm—Fe—N sintered magnet, and the degree of densification of the sintered body was evaluated. In Figure 4, the densification evaluation is indicated by "Good" for a degree of densification of 90% or more, "Average" for a degree of densification of 80% or more but less than 90%, and "Poor" for a degree of densification of less than 80%.

[0052] In the sintering evaluation, SmFe was crushed to an average particle size of 0.1 μm to 20 μm. 17 The auxiliary alloy powder of each sample was added to N3 powder at a ratio of 20 vol% or less, and sintered bodies were obtained by conducting electric sintering at a sintering temperature of 400°C to 600°C. The sinterability of the sintered bodies was evaluated from the structure images obtained by observing the cross section of the sintered body with a SEM (Scanning Electron Microscope). 17The theoretical density of N3 is 7.67 g / cm 3 In contrast, the specific gravity of alloys containing Group 2 elements is generally SmFe 17 The specific gravity is significantly lower than that of N3, and since the difference in specific gravity is large, it is not necessarily appropriate to use the actual density measured by the Archimedes method or the like for discussion.

[0053] To observe the cross section of the sintered body, a sample 100S for SEM observation was prepared from the sintered body produced by the above method. FIG. 5 is an explanatory diagram of the sample 100S for SEM observation. First, the sintered body (sintered magnet) produced by the above method was cut into a cylindrical shape with a diameter of 6 mm and a thickness of 3 mm (FIG. 5(A)). Then, a cross section was exposed using waterproof abrasive paper (FIG. 5(B)). The cross section was subjected to Ar ion milling to prepare the sample 100S for SEM observation (FIG. 5(C)).

[0054] Each SEM observation sample 100S was observed at a magnification of 3000 times or less, and both a secondary electron image and a backscattered electron image were obtained in the same field of view so that the porosity and the auxiliary component (auxiliary alloy powder) in the sintered body could be distinguished. The obtained sintered body photographs were binarized using the image processing software Image-J to calculate the porosity and the amount of the auxiliary component (auxiliary alloy powder), and the sum of these values ​​was subtracted from 100% to obtain the SmFe content. 17 The threshold value for the binarization process was determined by displaying in monochrome with 256 tones, with 0 being black and 255 being white, and by referring to section 28.2.4 Threshold in the Image 1.46 ver. manual, and setting the Auto Threshold method to default.

[0055] Since Mg, Ca, etc. are lighter elements than Sm and Fe, they appear relatively dark (black) in the backscattered electron image, so the alloy part was shown in black and the void was shown in white by adjusting the contrast so that the edge part in the secondary electron image was bright. On the other hand, Ba has a larger atomic number than Fe, so the difference in contrast in the backscattered electron image does not distinguish the alloy part from the SmFe part. 17Since it is difficult to calculate the area ratio of the N3 main phase, EDS (Energy Dispersive X-ray Spectroscopy) analysis was used for Sample 7. 17 The proportion of N3 was evaluated as the degree of densification of the sintered body.

[0056] 4, Samples 1 to 10 have a densification degree of 80% or more, which is higher than that of Sample 13, which does not contain auxiliary alloy powder. In contrast, Sample 12 has a densification degree of less than 80%, which is lower than that of Sample 13.

[0057] The auxiliary alloy powders of Samples 1 to 10 satisfy the following requirements [1] to [3] (Figure 4). [1] The content of Group 2 elements is 20 atomic percent or more and 90 atomic percent or less. [2] The average particle size is 0.1 μm or more and 30 μm or less. [3] A melting endothermic peak is observed at 620°C or less in differential scanning calorimetry.

[0058] In contrast, the auxiliary alloy powder of Sample 11 satisfies the requirements [1] and [3] above, but does not satisfy the requirement [2] above, and the auxiliary alloy powder of Sample 12 satisfies the requirements [1] and [2] above, but does not satisfy the requirement [3] above. The auxiliary alloy powders of Samples 1 to 10 were able to improve the densification of the Sm—Fe—N sintered body by satisfying the requirements [1] to [3] above.

[0059] It is believed that the auxiliary alloy powders of Samples 1 to 10 satisfied the requirement [3] above, allowing the Sm—Fe—N crystal grains to undergo liquid phase sintering, and also satisfied the requirement [2] above, resulting in a small average particle size, making it possible to obtain a dense sintered body (sintered magnet).The auxiliary alloy powders of Samples 11 and 12 did not satisfy either the requirement [2] or [3] above, and therefore could not sufficiently densify the Sm—Fe—N sintered body.

[0060] The auxiliary alloy powders of Samples 1 to 10 further satisfy the following requirement [4]. The auxiliary alloy powders of Samples 3 to 10 additionally satisfy the following requirement [5]. [4] The oxygen content is 10 mass% or less. [5] The nitrogen content is 1 mass% or more and 10 mass% or less.

[0061] As shown in FIG. 4, when the oxygen content is in the range of 10 mass % or less, the finer the particle size of the auxiliary alloy powder, the more the SmFe 17 It was confirmed that the sinterability of SmFeN3 was improved (Samples 1 to 10). Furthermore, it was confirmed that the auxiliary alloy powders of Samples 3 to 10 could reduce the average particle size and improve the densification of the sintered body compared to the auxiliary alloy powders of Samples 1 and 2, which contained less than 1% by mass of nitrogen. Within the range of 1 to 10% by mass of nitrogen content, the higher the nitrogen content, the better the sinterability of SmFeN3. 17 It was confirmed that the sinterability of N3 improved (Samples 3 to 10). When the nitrogen content exceeded 10 mass % as in the auxiliary alloy powder of Sample 3 and further pulverization proceeded, the oxygen content exceeded 10 mass %, and the melting point rose, resulting in the powder not being able to fully function as an auxiliary. 17 The sinterability of N3 was not improved.

[0062] The auxiliary alloy powders of Samples 5 to 10 further satisfy the following requirement [6]: [6] The average particle size is 0.1 μm or more and 10 μm or less. The sintered bodies using the auxiliary alloy powders of Samples 5 to 10 have improved sinterability and achieved a densification degree of 90% or more compared to the sintered bodies using the auxiliary alloy powders of Samples 1 to 4, which have an average particle size greater than 10 μm.

[0063] As explained above, Samples 1 to 10 satisfy all of the requirements [1] to [3] above, and are examples of the auxiliary alloy powder of the above embodiment. 17 When the N3 sintered body is produced, the Sm2Fe sintered body produced without adding auxiliary alloy powder is 17 It was confirmed that the degree of densification could be improved compared to the N3 sintered body, in other words, the sinterability could be improved.

[0064] FIG. 6 shows the evaluation results for Sample 14. For Sample 14, an auxiliary alloy powder was produced using gas atomization and thermal plasma. Similar to Samples 1 to 12, an Sm—Fe—N sintered magnet was produced and its density was evaluated. The average particle size of Sample 14 was calculated using an area measurement method using SEM images, rather than measurement using a dry particle size distribution analyzer (HELOS & RODOS: Sympatec). This was because the particle size was too small to be measured using the particle size distribution analyzer. Sample 14 uses barium (Ba) as the Group 2 element. Note that FIG. 6 shows the density of Sample 13, an Sm—Fe—N sintered magnet produced without the addition of auxiliary alloy powder. Sample 13 is the same as the one shown in FIG. 4.

[0065] As shown in FIG. 6, Sample 14 achieved a densification degree of 90% or more (93.9%), which is significantly improved over Sample 13, to which no auxiliary alloy powder was added.

[0066] The auxiliary alloy powder of sample 14 satisfies the above requirements [1] and [3], as well as the following requirement [2'] (FIG. 6): [2'] The average particle size is 0.01 μm or more and 0.1 μm or less.

[0067] The auxiliary alloy powder of Sample 14 satisfies the above requirement [3], allowing the Sm-Fe-N crystal grains to undergo liquid phase sintering. Furthermore, it also satisfies the above requirement [2'], and its small average particle size is believed to have enabled the production of a dense sintered body (sintered magnet). Thus, Sample 14 satisfies all of the above requirements [1], [2'], and [3], and is an example of the auxiliary alloy powder of the above embodiment. The auxiliary alloy powder of this sample was used to produce SmFeN crystal grains. 17 When the N3 sintered body is produced, the Sm2Fe sintered body produced without adding auxiliary alloy powder is 17 It was confirmed that the degree of densification could be improved compared to the N3 sintered body, in other words, the sinterability could be improved.

[0068] In the above example, the main phase particles of the sintered body were Th2Zn. 17 Sm2Fe of type structure 17N3 is exemplified, but there are also TbCu7 type structures containing Sm and Th2Mn 12 When producing a sintered body having other rare earth iron-based particles having a type structure as the main phase, the sinterability can be similarly improved by using the auxiliary metal powder of the above embodiment. As will be described later, the inventors have found that the sintered body can be produced by using the auxiliary metal powder of the above embodiment when the Group 2 element of the periodic table is SmFe. 17 It was proposed that the good wettability of these elements to N3 magnets is due to the reducing effect of these elements on Sm, a constituent element of sintered magnets. It can be considered that the wetting of the liquid phase to the solid phase will have a similar effect even if the constituent elements of both are similar. Therefore, although the crystal structures are different, the basic constituent elements are Sm and Fe, and their compound ratios are similar, so it is possible to use TbCu7 type structures and Th2Mn 12 For rare earth iron-based sintered magnets containing Sm, which have the Sm structure, the Group 2 element of the periodic table is SmFe. 17 It exhibits high wettability similar to sintered N3 magnets.

[0069] 4. Wettability of the Alloy Prior to the production of the above samples, Sm—Fe—N crystal grains (SmFe 17 A preliminary experiment was conducted to narrow down the element group and alloy composition that exhibit good wettability with Sm-Fe-N system crystal grains (SmFeN). Figure 7 shows the results of the alloy wettability evaluation. The alloy powder with the composition shown in Figure 7 was produced by the above-mentioned manufacturing method P2 (Figure 1). 17 The Sm-Fe-N crystal grains (SmFeN fine powder) were produced by the pulverization step P1 of the above-mentioned sintered magnet manufacturing method (Fig. 3). 17 The alloy powder was added at a ratio of 20 vol% to Sm-Fe-N fine powder, and the powder was subjected to electric pressure sintering at a sintering temperature of 450°C to 600°C for 10 minutes under a pressure of 600 MPa in a vacuum atmosphere. The porosity was calculated using the sintered bodies (samples S1 to S23), and these values ​​were compared for each alloy to determine the Sm-Fe-N system crystal grains (SmFe 17 An alloy composition with good wettability to the N3 fine powder was selected.

[0070] The sintered body (sintered magnet) produced by the above method was cut into a cylindrical shape with a diameter of 10 mm and a thickness of 3 mm, and a sample 100S for SEM observation was produced in the same manner as the sample 100S for SEM observation (FIG. 5). SEM observation was performed using the sample 100S for SEM observation, and secondary electron images were taken at 1000x magnification in five different locations in the field of view. The secondary electron images were binarized using the image processing software Image-J to calculate the porosity.

[0071] As shown in FIG. 7 , the metallic binders of samples S1 to S4 are binary alloys containing calcium (Ca), a Group 2 element; the metallic binders of samples S5 to S8 are binary alloys containing barium (Ba), a Group 2 element; and the metallic binder of sample S9 is a binary alloy containing magnesium (Mg), a Group 2 element. Among these, sample S6 is a binary alloy containing both barium (Ba) and magnesium (Mg) as Group 2 elements. Sample S10 is a ternary alloy containing calcium (Ca), a Group 2 element, and sample S11 is a ternary alloy containing barium (Ba), a Group 2 element. The metallic binders of samples S12 to S16 do not contain a Group 2 element. The sintered compact of sample S17 does not contain a metallic binder. The metal binders of samples S18 to S21 are ternary alloys containing calcium (Ca), a Group 2 element, and the metal binders of samples S22 and S23 are ternary alloys containing barium (Ba), a Group 2 element.

[0072] Preliminary experiments confirmed that the porosity was significantly reduced in the sintered bodies (samples S1 to S11 and S18 to S23) to which a metal binder containing a Group 2 element was added. That is, the metal binder in samples S1 to S11 and S18 to S23 was used to form Sm-Fe-N crystal grains (SmFe 17 It is believed that it exhibits good wettability with respect to the surface of the SiO2 nanoparticles (N3 fine powder).

[0073] In the preliminary experiments, magnesium (Mg), calcium (Ca), and barium (Ba) were used as Group 2 elements, but for the following reasons, it is believed that similar effects can be obtained by using other Group 2 elements such as beryllium (Be), strontium (Sr), and radium (Ra).

[0074] In the Ellingham diagram, calcium (Ca) is located below Sm, so Ca has the effect of reducing Sm over the entire temperature range. 17 It is also used as a reducing material for Sm oxide when chemically synthesizing N3 particles. 17 Since Ca is an element that undergoes a redox reaction with the unavoidable oxides present on the surface of particles with a N3-based main phase, alloys containing Ca also have a similar effect. "Occurrence of a redox reaction" can be rephrased as "having a certain level of reactivity with the main-phase particle surface," and wettability can also be considered a type of reactivity. Ca belongs to Group 2 of the periodic table, and its homologous elements, Be, Mg, Sr, Ba, and Ra, also have a reducing effect on Sm—Fe—O. Therefore, similar effects can be expected with other elements in the same group as Ca. In addition, in binary phase diagrams, element X (Be, Mg, Sr, Ba, and Ra) have a eutectic point when alloyed with Ca, and can achieve the minimum low melting point required for a binder.

[0075] Therefore, the inventors aimed to improve the volume fraction of the first phase (magnetic phase) by optimizing the composition and the amount of addition of the alloy containing the Group 2 element.

[0076] The present disclosure has been described above based on embodiments and examples, but the embodiments of the above-described aspects are intended to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present disclosure. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0077] The present disclosure can also be realized as the following application examples. [Application Example 1] An auxiliary alloy powder for a rare earth iron-based sintered magnet, characterized in that the content of a Group 2 element is 20 atomic % or more and 90 atomic % or less, the average particle size is 0.1 μm or more and 30 μm or less, and a melting endothermic peak is observed at 620°C or less in differential scanning calorimetry. [Application Example 2] The auxiliary alloy powder according to Application Example 1, characterized in that the oxygen content is 10 mass % or less. [Application Example 3] The auxiliary alloy powder according to Application Example 1 or Application Example 2, characterized in that the nitrogen content is 1 mass % or more and 10 mass % or less. [Application Example 4] The auxiliary alloy powder according to any one of Application Examples 1 to 3, characterized in that the average particle size is 0.1 μm or more and 10 μm or less. [Application Example 5] An auxiliary alloy powder for a rare earth iron-based sintered magnet, characterized in that the content of a Group 2 element is 20 atomic % or more and 90 atomic % or less, the average particle size is 0.01 μm or more and 0.1 μm or less, and a melting endothermic peak is observed at 620° C. or less in differential scanning calorimetry. [Application Example 6] A method for producing an auxiliary alloy powder according to any one of Application Examples 1 to 5, characterized in that it includes a step of producing the auxiliary alloy powder from an alloy ingot containing 20 atomic % or more and 90 atomic % or less of a Group 2 element in an atmosphere with a low oxygen concentration.

[0078] 10...First phase 10G...Sm-Fe-N crystal grains 20...Second phase 100...Sintered magnet 100S...Sample for SEM observation V...Void

Claims

1. An auxiliary alloy powder for rare earth iron-based sintered magnets, characterized in that the content of Group 2 elements is 20 atomic % or more and 90 atomic % or less, the average particle size is 0.1 μm or more and 30 μm or less, and a melting endothermic peak is observed at 620°C or less in differential scanning calorimetry.

2. The auxiliary alloy powder according to claim 1, characterized in that the oxygen content is 10 mass % or less.

3. The auxiliary alloy powder according to claim 1, characterized in that the nitrogen content is 1% by mass or more and 10% by mass or less.

4. The auxiliary alloy powder according to claim 1, characterized in that the average particle size is 0.1 μm or more and 10 μm or less.

5. An auxiliary alloy powder for a rare earth iron-based sintered magnet, characterized in that the content of a Group 2 element is 20 atomic % or more and 90 atomic % or less, the average particle size is 0.01 μm or more and 0.1 μm or less, and a melting endothermic peak is observed at 620°C or less in differential scanning calorimetry.

6. A method for producing an auxiliary alloy powder according to any one of claims 1 to 5, characterized in that it comprises a step of producing the auxiliary alloy powder from an alloy ingot containing 20 atomic % or more and 90 atomic % or less of a Group 2 element in an atmosphere with a low oxygen concentration.

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