Magnetic materials for bonded magnets and magnets

Abstract

The magnet material according to the present invention has a structure in which the main phase is an RE2Fe14B-type tetragonal compound and in which this main phase is surrounded by an amorphous grain boundary phase containing F, RE, Fe, and B (wherein RE is at least one rare earth element necessarily including at least Nd from Nd and Pr).

Description

[Technical Field]

[0001] The present invention relates to a magnetic material for a bonded magnet and to a magnet. [Background technology]

[0002] Patent Document 1 discloses a magnet in which a heavy rare earth fluoride is applied to the surface of a sintered magnet bulk, followed by heat treatment to diffuse the heavy rare earth into the magnet, thereby coating the main phase with a phase containing the heavy rare earth, thereby improving coercivity. Patent Document 2 discloses a magnet in which a rare earth-low melting point metal compound is applied to the surface of a hot-processed magnet bulk, followed by heat treatment to diffuse the rare earth into the magnet, thereby improving coercivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4450239 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-82626 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the magnetic materials described in these patent documents all involve a process of heat treatment of the bulk body, and therefore are not suitable for use in bonded magnets, where the resin in the bulk body is denatured and melted by heat treatment. For this reason, there has been a demand for a magnetic material for bonded magnets that exhibits a high intrinsic coercivity. The present invention has been made to solve the above problems, and aims to provide a magnetic material for bonded magnets and a magnet that exhibits a high intrinsic coercivity HcJ. [Means for solving the problem]

[0005] The magnetic material for bonded magnets according to the present invention is RE2Fe 14The structure is such that a B-type tetragonal compound is the main phase, and an amorphous grain boundary phase containing F, RE, Fe, and B surrounds the main phase (wherein RE is at least one rare earth element, which must contain at least Nd among Nd and Pr).

[0006] In the above-mentioned magnetic material for bonded magnets, the width of the grain boundary phase is preferably 1 nm or more and less than 10 nm.

[0007] In the above-mentioned magnetic material for bonded magnets, it is preferable that the content of the main phase is 70% by volume or more and 99% by volume or less, and the content of the grain boundary phase is 1% by volume or more and 30% by volume or less.

[0008] A magnet according to the present invention comprises a binder and any of the above-described magnetic materials for bonded magnets dispersed in the binder. [Effects of the Invention]

[0009] The magnetic material for bonded magnets and the magnet according to the present invention can exhibit a high intrinsic coercivity HcJ. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically showing an example of a magnetic material of the present invention. [Figure 2] 1 shows a powder X-ray diffraction profile of the rapidly solidified alloy obtained in Example 5. [Figure 3] (a) is a diagram showing the equipment configuration of a heat treatment furnace that realizes flash annealing, and (b) is a diagram showing the state of the rapidly solidified alloy moving inside the furnace tube. [Figure 4] FIG. 2 is a conceptual diagram of the thermal history of flash annealing performed in the present invention. [Figure 5] 1 shows a powder X-ray diffraction profile of the rapidly solidified alloy obtained in Example 5 after flash annealing (crystallization heat treatment). [Figure 6] 1 shows a bright-field image and element mapping of the magnet material obtained in Example 1 observed with a transmission electron microscope. [Figure 7] 1 shows a bright-field image and element mapping of the magnet material obtained in Example 2 observed with a transmission electron microscope. [Figure 8] 1 shows a bright-field image and element mapping of the magnet material obtained in Example 3 observed with a transmission electron microscope. [Figure 9] 1 shows a bright-field image and element mapping of the magnet material obtained in the comparative example observed with a transmission electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes the magnetic material for bonded magnets and the magnet of the present invention. Note that the present invention is not limited to the following configurations, and may be modified as appropriate without departing from the gist of the present invention. Furthermore, a combination of multiple individual preferred configurations described below also constitutes the present invention.

[0012] The magnetic material for bonded magnets according to the present invention is RE2Fe 14 This magnet material has a structure in which a B-type tetragonal compound is the main phase, surrounded by an amorphous grain boundary phase containing F, RE, Fe, and B (where RE is at least one rare earth element, including at least Nd among Nd and Pr). Figure 1 is a cross-sectional view showing a schematic example of this magnet material. As shown in Figure 1, in this magnet material, the main phase 21 is surrounded by the grain boundary phase 22. Note that if a similar composition containing at least F and B is produced using strip casting, mold casting, centrifugal casting, or other methods, a crystalline or crystalline grain boundary phase containing F (without or only trace amounts of B) is produced, and the grain boundary phase uniformly covering the main phase as in the present invention cannot be achieved. This is because, to produce the grain boundary phase as in the present invention, it is necessary to employ the melt spinning method, a rapid cooling method suitable for producing bonded magnets with a fine structure (e.g., a structure in which the average crystal size of the main phase is less than 70 nm), as described below. This is explained in detail below.

[0013] [Alloy composition] As described above, the alloy composition of the magnetic material for the bonded magnet of the present invention is RE2Fe14 There are no particular limitations on the structure as long as the main phase is a B-type tetragonal compound and the amorphous grain boundary phase containing F, RE, Fe, and B surrounds the main phase. For example, 100-x-y-z (B 1-n C n ) x RE y M z (T is at least one element selected from the group consisting of Fe, Co, and Ni, and is a transition metal element that must include Fe; RE is at least one rare earth element selected from the group consisting of Nd and Pr, and is at least one Nd; and M is one or more metal elements selected from the group consisting of Al, Si, V, Cr, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb), and the compositional ratios x, y, and z can be expressed as follows: 4.2 atomic %≦x≦5.6 atomic %, 11.5 atomic %≦y≦13.0 atomic %, 0.0 atomic %≦z≦5.0 atomic %, and 0.0≦n≦0.5, respectively. The composition of the magnetic material according to the present invention can be analyzed by ICP mass spectrometry or combustion ion chromatography. Combustion-infrared absorption spectrometry may also be used in combination, if necessary.

[0014] The transition metal element T, which contains Fe as an essential element, accounts for the remainder of the above-mentioned elements. The desired hard magnetic properties can also be obtained by substituting a portion of the Fe with one or both of Co and Ni, which are also ferromagnetic elements like Fe. However, since a substitution amount of more than 30% of Fe results in a significant decrease in magnetic flux density, the substitution amount is preferably in the range of 0% to 30%. The addition of Co not only contributes to improving magnetization but also reduces the viscosity of the molten metal, thereby stabilizing the melt tapping rate from the nozzle during quenching. Therefore, the Co substitution amount is more preferably 0.5% to 30%. From the viewpoint of cost-effectiveness, the Co substitution amount is even more preferably 0.5% to 10%.

[0015] In the magnetic material for bonded magnets of the present invention, for example, when the composition ratio x of B+C is less than 4.2 atomic %, RE2Fe 14If the amount of B+C necessary to form the B-type tetragonal compound cannot be secured, the magnetic properties and amorphous formation ability may be significantly reduced. This may result in the precipitation of an α-Fe phase during rapid solidification of the molten alloy, resulting in a loss of squareness in the demagnetization curve. Furthermore, if the B+C composition ratio x exceeds 5.6 atomic percent, the grain boundary phase primarily composed of RE and Fe may not be formed, potentially making it impossible to ensure the above-mentioned magnetic properties. Therefore, the composition ratio x is preferably set to a range of 4.2 atomic percent to 5.6 atomic percent. The composition ratio x is preferably set to a range of 4.2 atomic percent to 5.2 atomic percent, and more preferably set to a range of 4.4 atomic percent to 5.0 atomic percent.

[0016] In the magnetic material for bonded magnets of the present invention, by substituting a portion of B with C, the melting point of the molten alloy is lowered and the amount of wear on the refractory material used during rapid solidification is reduced, thereby reducing the process costs associated with rapid solidification and improving the intrinsic coercivity HcJ. However, if the substitution rate of C for B exceeds 50%, the amorphous formation ability is significantly reduced, which is not desirable. Therefore, the substitution rate of C for B is preferably in the range of 0% to 50%, i.e., 0.0≦n≦0.5. From the perspective of improving the intrinsic coercivity HcJ, the substitution rate of C for B is preferably 2% to 30%, and more preferably 3% to 15%.

[0017] In the magnet material for bonded magnets of the present invention, if the composition ratio y of at least one rare earth element RE, which must contain at least Nd among Nd and Pr, is less than 11.5 atomic %, there is a risk that a grain boundary phase containing F, RE, Fe, and B will not be generated, and sufficient magnetic properties may not be ensured. Furthermore, if the composition ratio y exceeds 13.0 atomic %, there is a risk that the magnetization will decrease. Therefore, the composition ratio y is preferably in the range of 11.5 atomic % or more and 13.0 atomic % or less. The F contained in the grain boundary phase is contained in Nd and Pr. That is, it is contained in Nd metal (Nd content of 95% by weight or more), Pr metal (Pr content of 95% by weight or more), or Nd-Pr metal (Nd / Pr weight ratio of 3.4 to 4.9% by weight, the sum of Nd and Pr of 95% by weight or more), which are raw materials used in production. Furthermore, from the viewpoint of ensuring a stable intrinsic coercivity HcJ, the composition ratio y is, for example, RE2Fe 14 It is preferably 11.76 atomic % or more and 13.0 atomic % or less, which is the stoichiometric composition of a B-type tetragonal compound, and more preferably 11.76 atomic % or more and 12.5 atomic % or less from the viewpoint of ensuring a high residual magnetic flux density Br.

[0018] In addition, the rare earth REs mentioned above are used to obtain higher intrinsic coercivity HcJ. y =(Nd 1-l Pr l ) y In this case, it is preferable that l is 0.05 or more and 0.7 or less. exchange If the coefficient l is too low, the effect of improving HcJ is small, and if l is too high, the absolute value of the temperature coefficient β related to the coercivity of the magnet alloy becomes small, which may result in a decrease in heat resistance. Therefore, l is preferably 0.15 or more and 0.6 or less, and more preferably 0.2 or more and 0.5 or less.

[0019] The magnetic material for bonded magnets of the present invention may contain one or more metal elements M selected from the group consisting of Al, Si, V, Cr, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb. The addition of metal elements M improves the amorphous formation ability, the intrinsic coercivity HcJ by uniformly refining the metal structure after crystallization heat treatment, and the squareness of the demagnetization curve, resulting in improved magnetic properties. However, since a composition ratio z of these metal elements M exceeding 5.0 atomic percent may result in a decrease in magnetization, the composition ratio z is preferably in the range of 0.0 atomic percent to 5.0 atomic percent. Furthermore, the composition ratio z is preferably in the range of 0.0 atomic percent to 4.0 atomic percent, and more preferably in the range of 0.0 atomic percent to 3.0 atomic percent.

[0020] [Metal structure] In the magnetic material for bonded magnets of the present invention, the main phase is RE2Fe 14 If the average crystal grain size of the B-type tetragonal compound is, for example, less than 10 nm, the intrinsic coercivity HcJ may decrease, and if it is, for example, 70 nm or more, the squareness of the demagnetization curve may decrease due to a decrease in the exchange interaction between the crystal grains. Therefore, for example, the remanence Br: 0.85 T or more, the intrinsic coercivity HcJ: 700 kA / m or more but less than 1400 kA / m, and the maximum energy product (BH)max: 120 kJ / m 3 To achieve the above magnetic properties, RE2Fe 14 The average crystal grain size of the B-type tetragonal compound is preferably in the range of 10 nm or more and less than 70 nm. 14 The average crystal grain size of the B-type tetragonal compound is preferably 15 nm or more and 60 nm or less, and more preferably 15 nm or more and 50 nm or less.

[0021] RE2Fe 14 The average crystal grain size of a B-type tetragonal compound means the average value of the equivalent circle diameters of each particle present in the field of view when the particle size of each particle is measured at three or more points by the line segment method using a transmission electron microscope (TEM).

[0022] If the width of the grain boundary phase is, for example, less than 1 nm, the bonding force acting between the main phase particles increases, which may lead to a decrease in the intrinsic coercivity HcJ. On the other hand, if the width of the grain boundary phase is, for example, 10 nm or more, the interparticle bonding weakens, which may lead to a decrease in the squareness of the demagnetization curve. sex Therefore, the width of the grain boundary phase is preferably 1 nm or more and less than 10 nm, more preferably 2 nm or more and 8 nm or less, and even more preferably 2 nm or more and 5 nm or less. The width of the grain boundary phase was determined by performing image analysis on a bright-field image taken using a scanning transmission electron microscope under conditions of an accelerating voltage of 200 kV and an observation magnification of 900,000 times.

[0023] In the magnet material for bonded magnets of the present invention, the main phase and grain boundary phase preferably comprise 70% or more but less than 99% by volume of the main phase, and 1% or more but less than 30% by volume of the grain boundary phase. Furthermore, the coverage of the outer periphery of the main phase by the grain boundary phase is preferably 40% or more but less than 99% of the periphery of the outer periphery of the main phase. This facilitates the realization of magnetic properties such as a remanence Br of 0.85 T or more, an intrinsic coercivity HcJ of 700 kA / m or more but less than 1400 kA / m, and a maximum energy product (BH)max of 120 kJ / m or more. The ratio of the main phase is preferably 80% or more but less than 99% by volume, and more preferably 90% or more but less than 98% by volume. The composition ratio of the main phase to the grain boundary phase and the coverage of the outer periphery of the main phase by the grain boundary phase were determined by performing image analysis on bright-field images taken using a scanning transmission electron microscope at an accelerating voltage of 200 kV and an observation magnification of 900,000 times.

[0024] In the magnetic material for bonded magnets of the present invention, the presence of F in the grain boundary phase contributes to the formation of an amorphous grain boundary phase. 14 The B phase and the grain boundary phase, which is uniformly present around the main phase and is mainly composed of F, RE, Fe, and B, are connected by strong exchange interactions in addition to magnetostatic interactions, and behave as if they were a single hard magnetic phase, resulting in the RE2Fe 14It was found that a high remanence Br and a high maximum energy product (BH)max can be obtained by improving the squareness of the demagnetization curve without compromising the intrinsic coercivity HcJ of the B phase. In particular, it is believed that the presence of the grain boundary phase described above contributes to the development of a high intrinsic coercivity HcJ, as will be described later.

[0025] [Magnetic properties] The magnetic material for bonded magnets of the present invention has, for example, a residual magnetic flux density Br of 0.82 T or more, an intrinsic coercivity HcJ of 700 kA / m or more but less than 1400 kA / m, and a maximum energy product (BH)max of 105 kJ / m. 3 It is preferable that the magnet exhibits magnetic properties of at least the above. When used in various rotating machines that are optimal for electrical equipment and home appliances of about 1 horsepower (750 W) or less, and in a magnetic circuit configuration in which a reverse magnetic field is easily applied to permanent magnets such as surface permanent magnet rotors (SPM rotors), the intrinsic coercivity HcJ is preferably 800 kA / m or more, and more preferably 950 kA / m or more. Note that if the intrinsic coercivity HcJ is 1400 kA / m or more, magnetization will decrease significantly, so the intrinsic coercivity HcJ is preferably 1300 kA / m or less, and more preferably 1250 kA / m or less. Furthermore, when an embedded magnet rotor (IPM rotor) or the like is used, it becomes possible to drive the motor at a higher operating point (permeance) than with an SPM rotor, so it is better to have as high a residual magnetic flux density Br as possible. However, when considering the balance with the intrinsic coercive force HcJ, the residual magnetic flux density Br is preferably 0.85 T or more, and more preferably 0.9 T or more.

[0026] For example, the reason why a residual magnetic flux density Br of 0.82T or more is preferable is that when used as an isotropic bonded magnet in a DC brushless motor, the operating point (permeance Pc) of the magnet is between 3 and 10, so if the residual magnetic flux density Br is 0.82T or more, within this Pc range, the maximum energy product (BH)max is 300kJ / m 3 The performance is equivalent to that of the above anisotropic Nd-Fe-B sintered magnets. EffectiveThis is because a magnetic flux Bm can be obtained. It is more preferable that the residual magnetic flux density Br is 0.86 T or more.

[0027] The reason why an intrinsic coercivity HcJ of 700 kA / m or more is preferable is that if the intrinsic coercivity HcJ is less than 700 kA / m and the magnet is applied as an isotropic bonded magnet to a DC brushless motor, the motor's heat resistance temperature cannot be guaranteed to 100°C, and there is a possibility that the desired motor characteristics will not be obtained due to thermal demagnetization. Additionally, the reason why the intrinsic coercivity HcJ is set to less than 1400 kA / m is that if the intrinsic coercivity HcJ is 1400 kA / m or more, magnetization becomes difficult, and multi-pole magnetization to ensure Pc: 3 or more and 10 or less becomes difficult.

[0028] Furthermore, the maximum energy product (BH) is 105 kJ / m 3 The reason why the above is preferable is that the maximum energy product (BH)max is 105kJ / m 3 Below this, the squareness ratio of the demagnetization curve (residual magnetization Jr / saturation magnetization Js) will be 0.8 or less, and if used as an isotropic bonded magnet in a DC brushless motor, the magnetic properties will deteriorate due to the reverse magnetic field generated during motor operation, and there is a possibility that the desired motor characteristics will not be obtained.

[0029] [Magnetic material manufacturing method] The magnetic material for bonded magnets of the present invention can be manufactured, for example, as follows: First, a molten alloy having the above-mentioned metal composition is prepared. Next, this molten alloy is sprayed onto the surface of a rotating roll whose main component is Cu, Mo, W, or an alloy containing at least one of these metals, at an average pouring rate of 200 g / min or more and less than 2000 g / min per orifice located at the tip of the nozzle, thereby producing RE2Fe. 14 A rapidly solidified alloy is produced that contains 1% by volume or more of either a crystalline phase including a B phase or an amorphous phase. RE is at least one rare earth element that is substantially free of La and Ce, but as an example, RE can be at least one rare earth element that necessarily contains at least Nd among Nd and Pr, as described above. Details are as described above.

[0030] [Quenching of molten metal] In the method for producing a magnet material of the present invention, raw materials prepared to have a predetermined alloy composition are melted to produce a molten alloy, and then the molten alloy is sprayed onto the surface of a rotating roll whose main component is Cu, Mo, W, or an alloy containing at least one of these metals at an average pouring rate of 200 g / min or more and less than 2000 g / min per orifice provided at the tip of a nozzle, thereby producing RE2Fe 14 A rapidly solidified alloy containing at least 1% by volume of either a crystalline phase, including a B phase, or an amorphous phase is produced. However, if the average tapping rate is less than 200 g / min, productivity is poor, and if it is more than 2000 g / min, the rapidly solidified alloy structure will contain a coarse α-Fe phase, which may prevent the magnetic properties from being achieved even after crystallization heat treatment. Therefore, the average tapping rate per orifice located at the tip of the nozzle is limited to a range of 200 g / min or more and less than 2000 g / min. The average tapping rate is preferably 300 g / min or more and 1500 g / min or less, and more preferably 400 g / min or more and 1300 g / min or less.

[0031] The hole at the nozzle tip through which the molten metal is discharged does not have to be a circular orifice; it can be any shape, such as square, triangular, elliptical, etc., and a slit shape is also acceptable as long as it can ensure a predetermined dispensing rate. In addition, the nozzle material is acceptable as long as it is a refractory material that does not or is difficult to react with the molten alloy, but ceramic materials such as SiC, C, or BN are preferred, as they cause little wear to the nozzle orifice due to the molten metal during dispensing, and BN is more preferred, with hard BN containing an additive being even more preferred.

[0032] When producing the above-mentioned rapidly solidified alloy, an oxygen-free or low-oxygen atmosphere is preferred as the rapid solidification atmosphere, since this prevents oxidation of the molten alloy, suppresses an increase in the viscosity of the molten alloy, and maintains a stable tapping rate. To achieve this atmosphere, it is preferable to evacuate the rapid solidification apparatus to 20 Pa or less, preferably 10 Pa or less, and more preferably 1 Pa or less, and then introduce an inert gas into the rapid solidification apparatus to adjust the oxygen concentration inside the apparatus to 500 ppm or less, preferably 200 ppm or less, and more preferably 100 ppm or less, before performing the rapid solidification. As the inert gas, a rare gas such as helium or argon or nitrogen can be used. However, since nitrogen is relatively reactive with rare earth elements and iron, a rare gas such as helium or argon is preferred, and argon gas is more preferred from a cost perspective.

[0033] In the process of producing a rapidly solidified alloy, the rotating roll used to rapidly cool the molten alloy is primarily composed of Cu, Mo, W, or an alloy containing at least one of these metals. It is preferable for the rotating roll to have a base material containing such a primary component. This is because these base materials have excellent thermal conductivity and durability. Furthermore, plating the surface of the rotating roll base with Cr, Ni, or a combination thereof can enhance the heat resistance and hardness of the rotating roll base surface and suppress melting and deterioration of the rotating roll base surface during rapid solidification. The diameter of the rotating roll is, for example, Φ200 mm or more and Φ20,000 mm or less. If the rapid solidification time is short, 10 seconds or less, water cooling of the rotating roll is not necessary. However, if the rapid solidification time exceeds 10 seconds, it is preferable to flow cooling water inside the rotating roll to suppress temperature rise of the rotating roll base material. The water cooling capacity of the rotating roll is preferably calculated based on the latent heat of solidification per unit time and the melt tapping rate, and is optimally adjusted as appropriate.

[0034] [Flash Annealing] The method for producing a magnetic material of the present invention may further include a step of flash annealing the rapidly solidified alloy, in which the alloy is heated at a rate of 10°C / sec or more and less than 200°C / sec to a constant temperature range of not less than the crystallization temperature but not more than 850°C, and then rapidly cooled after a lapse of not less than 0.1 sec but less than 7 min. This flash annealing step produces RE2Fe 14 It is possible to form the above-mentioned metal structure even though the B content is lower than that of the stoichiometric composition of the B-type tetragonal compound.

[0035] If the heating rate during flash annealing (crystallization heat treatment) is less than 10°C / sec, excessive grain growth may prevent a fine metal structure from being obtained, and the intrinsic coercivity HcJ and remanence Br may decrease. If the heating rate is 200°C / sec or higher, crystal grain growth may not be fast enough to form the above-mentioned metal structure, and similarly to a heating rate of less than 10°C / sec, there is a risk of a decrease in magnetic properties. Therefore, the heating rate is preferably 10°C / sec or higher but less than 200°C / sec, more preferably 30°C / sec or higher but 200°C / sec or lower, and even more preferably 40°C / sec or higher but 180°C / sec or lower.

[0036] In this flash annealing (crystallization heat treatment), in order to obtain good magnetic properties, it is preferable to immediately quench the material after it reaches the crystallization heat treatment temperature (holding temperature) in a constant temperature range of above the crystallization temperature and below 850°C. More specifically, a holding time of substantially 0.1 seconds or more after reaching the crystallization heat treatment temperature and before quenching is sufficient; holding for 7 minutes or more is undesirable because it damages the uniform and fine metal structure and leads to a deterioration of various magnetic properties. Therefore, a holding time of 0.1 seconds or more but less than 7 minutes is preferable, more preferably 0.1 seconds or more but 2 minutes or less, and even more preferably 0.1 seconds or more but 30 seconds or less.

[0037] In this flash annealing (crystallization heat treatment), it is preferable to cool the rapidly solidified alloy to 400°C or less at a temperature drop rate of 2°C / sec or more and 200°C / sec or less. If the temperature drop rate is less than 2°C / sec, the crystalline structure will become coarse, and if it exceeds 200°C / sec, the alloy may oxidize. Therefore, the temperature drop rate is preferably 2°C / sec or more and 200°C / sec or less, more preferably 5°C / sec or more and 200°C / sec or less, and even more preferably 5°C / sec or more and 150°C / sec or less.

[0038] The flash annealing (crystallization heat treatment) is preferably performed in an inert gas atmosphere to prevent oxidation of the rapidly solidified alloy. As the inert gas, rare gases such as helium and argon, or nitrogen can be used. However, since nitrogen reacts relatively easily with rare earth elements and iron, rare gases such as helium and argon are preferred, and argon gas is more preferred from the viewpoint of cost.

[0039] [Crushing and molding] The method for producing a magnetic material for a bonded magnet of the present invention may further include a step of producing magnetic powder by pulverizing the rapidly solidified alloy or the rapidly solidified alloy that has been subjected to the flash annealing.

[0040] The rapidly solidified alloy obtained through the above process may be roughly cut or crushed into thin ribbons, for example, to 50 mm or less, before flash annealing (crystallization heat treatment).Furthermore, by crushing the rapidly solidified alloy after flash annealing (crystallization heat treatment) to an appropriate average powder particle size in the range of 20 μm to 200 μm to form a powdered magnetic material, this magnetic material can be used to manufacture various resin-bonded permanent magnets (commonly known as plastic magnets or bonded magnets) using known processes.

[0041] The permanent magnet of the present invention can be manufactured, for example, as follows: First, the powdered magnet material manufactured as described above is prepared. Next, a thermosetting resin is added to this magnet material, which is then filled into a molding die and compression-molded into a compact. This compact is then heat-treated at a temperature equal to or higher than the polymerization temperature of the thermosetting resin.

[0042] Alternatively, after preparing the powdered magnet material, a thermoplastic resin can be added to the magnet material to prepare an injection molding compound, which can then be injection molded.

[0043] When producing the magnet, the powdered magnetic material is mixed with, for example, epoxy, polyamide, polyphenylene sulfide (PPS), liquid crystal polymer, acrylic, polyether, etc., and molded into a desired shape. In this case, a hybrid magnetic powder mixed with permanent magnetic powder such as SmFeN magnetic powder or hard ferrite magnetic powder may also be used.

[0044] Using the magnets described above, it is possible to manufacture various rotating machines that can be used as brushless DC motors of approximately 1 horsepower (750 W) or less for automobiles (including electric vehicles and hybrid vehicles) and white goods, as well as various magnetic sensors.

[0045] When the powdered magnetic material is used for injection-molded bonded magnets, it is preferably pulverized to an average particle size of 100 μm or less, with the more preferred average crystal grain size of 20 μm to 100 μm. When it is used for compression-molded bonded magnets, it is preferably pulverized to an average particle size of 200 μm or less, with the more preferred average crystal grain size of 50 μm to 150 μm. Even more preferably, the particle size distribution has two peaks, with the average crystal grain size being 80 μm to 130 μm.

[0046] Furthermore, by subjecting the surface of the magnetic material for bonded magnets of the present invention to surface treatments such as coupling treatment and chemical conversion treatment (including phosphate treatment and glass coating treatment), it is possible to improve the moldability during molding of the resin-bonded permanent magnet and the corrosion resistance and heat resistance of the resulting resin-bonded permanent magnet, regardless of the molding method. In addition, even if the surface of the resin-bonded permanent magnet after molding is subjected to surface treatments such as resin painting, chemical conversion treatment and plating, it is possible to improve the corrosion resistance and heat resistance of the resin-bonded permanent magnet, just like the surface treatment of the magnet alloy powder.

[0047] The manufacturing method of the magnetic material for the bonded magnet of the present invention is not limited to the above, and other manufacturing methods can be adopted as long as they can produce a magnetic material having the above-mentioned composition, average crystal grain size, etc. For example, by using flash annealing, it is possible to produce RE2Fe with an average crystal grain size of 10 nm or more and less than 70 nm. 14 It is possible to form a fine metal structure with a B-type tetragonal compound as the main phase, but the formation of such a fine metal structure is not limited to flash annealing, and other methods can also be used. For example, even when a normal annealing process is used instead of flash annealing, good magnetic properties can be obtained by adjusting the surface speed of the rotating roll that quenches the molten alloy to form a homogeneous fine metal structure with crystal grains that are 5% to 20% smaller than the alloy structure that provides optimal magnetic properties. [Example]

[0048] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0049] (Example) 100 g of raw materials containing the major elements Nd, Pr, Dy, B, C, and Fe with a purity of 99.5% or higher, as well as additive elements such as Co, Al, Si, V, Cr, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb, were placed in an alumina melting crucible and then placed in the work coil of a vacuum melting furnace. The vacuum melting furnace was then evacuated to 0.02 Pa or less, and argon gas was introduced to atmospheric pressure. The molten alloy was then produced by high-frequency induction heating. The molten alloy was then poured into a water-cooled copper mold to produce the master alloy.

[0050] The resulting master alloy was then broken into pieces of appropriate size and inserted into a transparent quartz nozzle with an orifice of varying diameters (0.7 mm to 1.2 mm) at the bottom to achieve an average melting rate of 200 g / min or more but less than 2000 g / min. The nozzle was then placed in the work coil of a single-roll quenching apparatus. The vacuum melting furnace was then evacuated to 0.02 Pa or less, and argon gas was introduced to a quenching ambient pressure (40 to 65 kPa). The master alloy was remelted by high-frequency induction heating. The molten alloy was then ejected from the nozzle orifice at a pressure of 30 kPa onto the surface of a rotating roll rotating at a surface speed of 50 to 70 m / s, producing a rapidly solidified alloy. This process is referred to as the melt spinning method. The distance between the nozzle tip and the rotating roll surface was 0.8 mm. The main component of the rotating roll was copper. The rapidly solidified alloy obtained was NdFe 14 The material contained 1% by volume or more of either a crystalline phase including phase B or an amorphous phase.

[0051] As a representative example, Figure 2 shows the powder X-ray diffraction profile of the rapidly solidified alloy obtained in Example 5. As can be seen from Figure 2, Nd2Fe 14 The presence of phase B was confirmed.

[0052] The rapidly solidified alloy obtained in the above process was coarsely crushed to a few millimeters or less to obtain rapidly solidified alloy powder. The rapidly solidified alloy coarse powder was then placed in a flash annealing furnace (crystallization heat treatment furnace; muffle tube: transparent quartz, 15 mm outer diameter x 12.5 mm inner diameter x 1000 mm length, 300 mm heating zone, 500 mm cooling zone with cooling fan) and heat-treated at a workpiece cutting rate of 20 g / min. The muffle tube tilt angle, muffle tube rotation speed, and muffle tube vibration frequency were adjusted to achieve a heating rate of 10–200 °C / sec. The heat treatment temperature was set to 550–750 °C and the heat treatment time was set to 10–30 sec. As a result, the rapidly solidified alloy powder passed through the muffle tube while undergoing a combination of stirring due to the muffle tube rotation and hopping due to the muffle tube vibration. This resulted in unique heat treatment conditions in which the rapidly solidified alloy powder was subjected to thermal history individually, rather than as a single powder. An example of a heat treatment furnace and a thermal history in the flash annealing step are shown in FIGS. 3 and 4, respectively.

[0053] The constituent phases of the rapidly solidified alloy powder after flash annealing (crystallization heat treatment) were confirmed by powder X-ray diffraction. 14 The presence of phase B was confirmed. Figure 5 shows, as a representative example, the powder X-ray diffraction profile of the rapidly solidified alloy obtained in Example 5 after flash annealing (crystallization heat treatment).

[0054] 6 to 8 show bright-field images of the magnet materials obtained in Examples 1 to 3 observed with a transmission electron microscope and elemental mapping by energy dispersive X-ray analysis. The bright-field images show that NdFe 14 B phase and NdFe 14The presence of a clear grain boundary phase surrounding the B phase was confirmed. In addition, elemental mapping confirmed the presence of a grain boundary phase enriched with F and Nd or Pr at the grain boundaries of the main phase consisting of the main constituent elements Nd, Fe, and B. For example, in the elemental mapping of F, the white areas indicate F, which is found to be distributed along the grain boundary phase. The inventors have confirmed that the grain boundary phases shown in Figures 6 to 8 were formed in all examples. Furthermore, for the analysis of B, methods such as electron energy loss spectroscopy may be used as necessary.

[0055] As described above, the magnetic material obtained by flash annealing (crystallization heat treatment) was cut into a sample for magnetic property evaluation, measuring approximately 7 mm in length, approximately 0.9 mm or more and 2.3 mm or less in width, and 18 μm or more and 25 μm or less in thickness. It was then magnetized longitudinally using a pulsed magnetic field of 3.2 MA / m. The sample for magnetic property evaluation was then set longitudinally to suppress the effects of demagnetizing fields, and the room temperature magnetic properties were measured using a vibrating sample magnetometer (VSM). The results are shown in Table 2. It was found that Examples 2 and 3, which contain Pr, in particular, had a higher intrinsic coercivity HcJ than the other Examples.

[0056] Next, the flash-annealed (crystallization heat-treated) magnetic powder obtained in Example 5 was pulverized in a pin-disk mill to an average particle size of 125 μm. 2 mass% of epoxy resin diluted with methyl ethyl ketone (MEK) was then added to this pulverized magnetic powder, and after mixing and kneading, 0.1 mass% of calcium stearate was added as a lubricant to prepare a compound for compression-molded bonded magnets.

[0057] The above compound for compression-molded bonded magnets was compressed at 1568 MPa (16 ton / cm 2 The magnet was compressed at a pressure of 1000 kJ / cm² to obtain a compact measuring 10 mm in diameter and 7 mm in height. This compact was then subjected to a curing heat treatment (curing) at 180°C for 1 hour in an argon gas atmosphere to obtain an isotropic compression-molded bonded magnet. The density of the resulting isotropic compression-molded bonded magnet was 6.3 g / cm². 3(The true specific gravity of the magnetic powder is 7.5 g / cm 3 ), the magnetic powder filling rate was 84% ​​by volume.

[0058] The magnetic properties of the isotropic compression molded bonded magnet obtained using the magnetic powder of Example 5 were measured using a BH tracer after magnetizing it in the longitudinal direction with a pulsed magnetic field of 3.2 MA / m. The results were a residual magnetic flux density Br of 0.74 T, an intrinsic coercive force HcJ of 1028 kA / m, and a maximum energy product (BH)max of 89.4 kJ / m. 3 It was found that the magnetic properties of

[0059] Next, the flash-annealed (crystallization heat-treated) magnetic powder obtained in Example 5 was pulverized in a pin-disk mill to an average particle size of 75 μm. Then, while heating and stirring this pulverized magnetic powder, 0.75 mass% of a titanate-based coupling agent was sprayed onto the powder to perform a coupling treatment. After that, 0.5 mass% of stearic acid amide and 4.75 mass% of nylon 12 resin powder were added and mixed as a lubricant, and a compound for injection-molded bonded magnets was produced using a continuous extrusion kneader at an extrusion temperature of 170°C.

[0060] The compound for injection-molded bonded magnets was injection-molded at an injection temperature of 250°C to produce isotropic injection-molded bonded magnets with a diameter of 10 mm and a height of 7 mm. The density of the resulting isotropic injection-molded bonded magnet was 4.6 g / cm. 3 (The true specific gravity of the magnetic powder is 7.5 g / cm 3 ), the magnetic powder filling rate was 61% by volume.

[0061] The magnetic properties of the isotropic injection molded bonded magnet obtained using the magnetic powder of Example 5 were measured using a BH tracer after being magnetized in the longitudinal direction with a pulsed magnetic field of 3.2 MA / m. The results were a residual magnetic flux density Br of 0.54 T, an intrinsic coercive force HcJ of 1014 kA / m, and a maximum energy product (BH)max of 63.4 kJ / m. 3 It was found that, despite being injection molded, it was possible to obtain magnetic properties at the same level as general-purpose isotropic Nd-Fe-B compression molded bonded magnets.

[0062] (Comparative Example) As a comparative magnetic material, MQP-14-12 manufactured by Magnequench was prepared. Figure 9 shows a bright-field image and elemental mapping of the comparative magnetic material observed with a transmission electron microscope. The bright-field image shows NdFe with an average crystal grain size of 50 nm or less. 14 Although phase B was confirmed, no clear grain boundary phase was identified. In addition, elemental mapping also revealed that the grain boundary phases enriched with F and Nd or Pr, as seen in the examples, were not present at the crystal grain boundaries of the main phase consisting of the main constituent elements Nd, Fe, and B.

[0063] Furthermore, the magnet material according to the comparative example was cut into a sample for evaluating magnetic properties, measuring approximately 7 mm in length, approximately 0.9 mm or more and 2.3 mm or less in width, and 18 μm or more and 25 μm or less in thickness, and then magnetized in the longitudinal direction with a pulsed magnetic field of 3.2 MA / m. The sample for evaluation of magnetic properties was then set longitudinally to suppress the effects of the demagnetizing field, and the room temperature magnetic properties were measured using a vibrating sample magnetometer (VSM). The results are shown in Table 3. Table 3 shows that the intrinsic coercivity HcJ was lower than that of the examples.

[0064] [Table 1]

[0065] [Table 2] [Explanation of symbols]

[0066] 1 Raw material hopper 2. Raw material supply feeder 3. Furnace tube 3a Enlarged view of the furnace tube 3b Enlarged cross section of the furnace tube 4 tube furnace 5 cooling tower 6 Collection Hopper 7. Oscillators 8. Furnace tube rotation motor 9. Core tube rotation axis 10. Device stand 11. Furnace tube tilt angle 12 Cooling fan wind 13 Rapidly solidified alloy powder (workpiece) 14 Workpiece movement direction 15 Workpiece hopping phenomenon 16 Heating rate 17 Holding temperature 18 Cooling rate 21 Main phase 22 Grain boundary phase

Claims

1. RE having an average crystal grain size of 10 nm or more and less than 70 nm 2 Fe 14 The alloy has a structure in which a B-type tetragonal compound is a main phase, and a grain boundary phase, which is an amorphous and magnetic phase containing F, RE, Fe, and B, surrounds the main phase, The width of the grain boundary phase is 1 nm or more and less than 10 nm. A magnetic material for bonded magnets (where RE is at least one rare earth element, which must contain at least Nd out of Nd and Pr).

2. The magnetic material for a bonded magnet according to claim 1 , wherein the RE contains Nd and Pr.

3. A magnetic material for a bonded magnet as described in claim 1, having an intrinsic coercive force of 700 kA / m or more.

4. A magnetic material for a bonded magnet as described in claim 3, having a residual magnetic flux density of 0.82 T or more.

5. The content of the main phase is 70% by volume or more and 99% by volume or less, 2. The magnetic material for a bonded magnet according to claim 1, wherein the content of the grain boundary phase is 1% by volume or more and 30% by volume or less.

6. A binder and The magnetic material for a bonded magnet according to any one of claims 1 to 5, dispersed in the binder; A magnet is provided.

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