Rare earth magnets

Abstract

To provide an R-Fe-B rare earth magnet that exhibits a small decrease in coercive force as temperature rises and has excellent desorption magnetism at room temperature.SOLUTION: A rare earth magnet according to the present invention includes a main phase 10 having a crystal structure of R2Fe14B type (where R is a rare earth element) and a grain boundary phase 20 existing around the main phase 10. In the rare earth magnet according to the present disclosure, at least Ce and La are selected as R, a part of Fe is substituted with Co, and the molar ratio of Co to the total of Fe and Co is 0.20 to 0.25.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to rare earth magnets. In particular, this disclosure relates to R-Fe-B type rare earth magnets (where R is a rare earth element). [Background technology]

[0002] R-Fe-B rare earth magnets consist of a main phase and a grain boundary phase surrounding the main phase. The main phase is R2Fe 14 This is a magnetic phase with a type B crystal structure. This main phase allows for high remanent magnetization. For this reason, R-Fe-B rare earth magnets are often used in motors.

[0003] Since motors generate heat during operation, the permanent magnets used in motors are required to have high coercivity at high temperatures. In this specification, unless otherwise specified, high temperature in relation to magnetic properties means temperatures in the range of 100 to 200°C, and especially 140 to 180°C.

[0004] While Nd has primarily been selected as the R component in R-Fe-B rare earth magnets, the rapid spread of electric vehicles and other technologies is leading to concerns about increased Nd usage and thus its increasing scarcity. For this reason, the use of light rare earth elements, which are less scarce than Nd, is being considered. For example, Patent Document 1 discloses an R-Fe-B rare earth magnet in which Ce and La, both light rare earth elements, are selected as the R component. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 61-159708 [Overview of the project] [Problems that the invention aims to solve]

[0006] As with the R-Fe-B rare-earth magnet disclosed in Patent Document 1, simply selecting a light rare-earth element as R reduces the coercivity. One application of a permanent magnet with relatively low coercivity is a variable field motor.

[0007] Coercivity decreases with increasing temperature. Therefore, if high coercivity is maintained at high temperatures, the coercivity at room temperature becomes very high, resulting in poor demagnetization at room temperature. For example, in applications where demagnetization occurs at different temperatures, such as variable field motors, a small decrease in coercivity with increasing temperature is expected.

[0008] Based on these findings, the inventors identified a need for an R-Fe-B rare-earth magnet that exhibits minimal decrease in coercivity with increasing temperature and excellent demagnetization properties at room temperature.

[0009] This disclosure was made to solve the above-mentioned problems. The purpose of this disclosure is to provide an R-Fe-B rare-earth magnet that exhibits little decrease in coercivity with increasing temperature and excellent demagnetization properties at room temperature. [Means for solving the problem]

[0010] To achieve the above objective, the inventors have diligently conducted research and completed the rare earth magnet described herein. The rare earth magnet described herein includes the following embodiments. <1> R2Fe 14 It comprises a main phase having a type B crystal structure (where R is a rare earth element) and a grain boundary phase surrounding the main phase. As R, at least Ce and La have been selected. Some of the Fe is substituted with Co, and The molar ratio of Co to the total amount of Fe is between 0.20 and 0.25. Rare earth magnets. [Effects of the Invention]

[0011] According to this disclosure, by selecting at least Ce and La as R, and substituting a portion of Fe with a predetermined proportion of Co, it is possible to provide an R-Fe-B rare earth magnet that exhibits a small decrease in coercivity with increasing temperature and excellent demagnetization properties at room temperature. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram illustrating an example of the microstructure of the rare earth magnet described herein. [Figure 2] Figure 2 is a schematic diagram illustrating a cooling device used in the liquid rapid cooling method. [Figure 3] Figure 3 is a schematic diagram illustrating a cooling device used in the strip casting method. [Figure 4] Figure 4 is a graph showing the relationship between temperature and coercivity for the samples in Examples 1-2, Comparative Example 4, and Comparative Example 7. [Modes for carrying out the invention]

[0013] The embodiments of the rare earth magnets of this disclosure will be described in detail below. Note that the embodiments described below are not limiting to the rare earth magnets of this disclosure.

[0014] The inventors' findings regarding the small decrease in coercivity with increasing temperature and excellent demagnetization performance at room temperature will be explained with reference to the drawings.

[0015] Figure 1 is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet according to this disclosure. The rare-earth magnet 100 according to this disclosure comprises a main phase 10 and a grain boundary phase 20 surrounding the main phase.

[0016] To improve desorption magnetism, reducing coercivity is effective. To reduce coercivity, selecting a light rare earth element as R is effective. Since light rare earth elements are less scarce and cheaper than Nd, selecting them is advantageous as it contributes to reducing the manufacturing cost of rare earth magnets. However, in R-Fe-B rare earth magnets, coercivity decreases with increasing temperature. If the coercivity at room temperature is low, the coercivity at high temperatures becomes excessively low, rendering the magnet unable to function as a permanent magnet, especially one used in motors. This is particularly pronounced when a light rare earth element is selected as R.

[0017] Therefore, when light rare earth elements, particularly Ce and La, are selected as R, the inventors have found that by substituting a portion of Fe with a predetermined proportion of Co, the decrease in coercivity with increasing temperature is reduced. Such R-Fe-B rare earth magnets have coercivity that functions as a permanent magnet, especially a permanent magnet used in motors, at high temperatures, but their coercivity at room temperature is not excessive, thus exhibiting excellent demagnetization properties at room temperature.

[0018] Although not bound by theory, by selecting Ce and La as light rare earth elements and substituting a portion of Fe with a predetermined proportion of Co, a phase (not shown) having an RFe2 type crystal structure is easily formed in the grain boundary phase 20 of Figure 1, while maintaining magnetic anisotropy at high temperatures. Since the phase having an RFe2 type crystal structure is a ferromagnetic phase, it particularly reduces coercivity at room temperature. For these reasons, the rare earth magnet of this disclosure exhibits little decrease in coercivity with increasing temperature and excellent demagnetization properties at room temperature.

[0019] In this specification, the decrease in coercivity with increasing temperature is evaluated using the temperature coefficient α unless otherwise specified. The temperature coefficient α is calculated by the following equation, and the smaller the absolute value of α, the smaller the decrease in coercivity with increasing temperature, and the better the demagnetization performance at room temperature. However, in the following equation, H c1 This is the coercivity at 27°C, H c2 This is the coercivity at 180°C. Temperature coefficient α(% / ℃)=[{(H c2 -H c1 )) / Hc1} / (180 °C - 27 °C)) × 100

[0020] Based on these findings, the constituent elements of the rare earth magnet of the present disclosure will be described below.

[0021] 《Rare Earth Magnet》 As shown in FIG. 1, the rare earth magnet 100 of the present disclosure includes a main phase 10 and a grain boundary phase 20. The grain boundary phase 20 exists around the main phase 10. Hereinafter, the main phase and the grain boundary phase will be described respectively.

[0022] 〈Main Phase〉 The main phase has a R2Fe 14 B-type crystal structure. R2Fe 14 The phase having a B “type” crystal structure means that a part of Fe may be substituted with a predetermined ratio of Co. Further, the main phase means that, as long as it can maintain its hard magnetism, it may contain elements other than R, Fe, Co, and B, particularly metal elements, in a substitutional and / or interstitial type.

[0023] There is no particular limitation on the volume ratio of the main phase. For example, it may be 80% by volume or more, 85% by volume or more, 90% by volume or more, 92% by volume or more, or 94% by volume or more, and may be 99% by volume or less, 98% by volume or less, 97% by volume or less, 96% by volume or less, or 95% by volume or less.

[0024] The volume ratio of the main phase is calculated from the content ratios (molar ratios) of rare earth elements, transition metal elements, and boron. The phases constituting the alloy are divided into a phase (main phase) having a R2Fe 14 B-type crystal structure (main phase) and a grain boundary phase, and the phase ratios are calculated from the molar ratio of the entire alloy. Since the change in the volume ratio of the main phase before and after the diffusion penetration of the modifier is small, it may be calculated from the boron content ratio (molar ratio) before the diffusion penetration of the modifier.

[0025] There is no particular limitation on the particle size of the main phase, but it is preferably nanocrystallized. By being nanocrystallized, the decrease in coercive force accompanying the temperature rise is small, and the desorption magnetism at room temperature is more remarkably excellent. <

[0026] In this specification, unless otherwise specified, "the main phase is nanocrystalline" means that the average particle size of the main phase is less than 1.0 μm. The average particle size of the nanocrystalline main phase may typically be 0.05 μm or more, 0.10 μm or more, 0.20 μm or more, 0.30 μm or more, 0.40 μm or more, or 0.50 μm or more, and may be 0.90 μm or less, 0.80 μm or less, 0.70 μm or less, or 0.60 μm or less.

[0027] If the main phase is not nanocrystalline, the average particle size of the main phase is typically 1.0 μm or more, 2.0 μm or more, 3.0 μm or more, 4.0 μm or more, 5.0 μm or more, or 6.0 μm or more, and may be 10.0 μm or less, 9.0 μm or less, 8.0 μm or less, or 7.0 μm or less.

[0028] The "average particle size" is measured as follows: A certain region is defined in a scanning electron microscope image or a transmission electron microscope image, observed from a direction perpendicular to the easy magnetization axis. Multiple lines are drawn perpendicular to the easy magnetization axis for the main phase within this region, and the diameter (length) of the main phase is calculated from the distance between the points where the lines intersect within the main phase particles (section method). If the cross-section of the main phase is close to a circle, it is converted using the projected area equivalent diameter. If the cross-section of the main phase is close to a rectangle, it is converted using the cuboid approximation. The diameter (length) distribution (particle size distribution) obtained in this way is D 50 This value represents the average particle size.

[0029] <Grain boundary phase> As mentioned above, the grain boundary phase exists around the main phase. This is why R-Fe-B rare earth magnets are R2Fe 14 This is because it is obtained by solidifying a molten metal containing more R than the theoretical composition of B (11.8 atomic percent R, 82.3 atomic percent Fe, and 5.9 atomic percent B). 14 A phase having a type B crystal structure, i.e., the main phase, can be stably obtained. In the following explanation, R2Fe 14 A molten metal containing more R than the theoretical composition of B is called "R-rich molten metal," and R2Fe 14The phase having a type B crystal structure is called "R2Fe 14 There is a term called "Phase B".

[0030] When R-rich molten metal is solidified, an ingot (including thin strips and / or flakes, etc.) is obtained that has a main phase and grain boundary phases surrounding the main phase. The main phase is R2Fe 14 It is phase B, R2Fe 14 Phase B is formed in the early stages of solidification of R-rich molten metal. R2Fe 14 Since the grain boundary phase is formed from the residual liquid after the formation of phase B, phases of various compositions are mixed within the grain boundary phase, and the overall composition of the grain boundary phase is R2Fe 14 It contains more R than the B phase. For this reason, the grain boundary phase is sometimes referred to as the R-rich phase. The rare earth magnet of this disclosure is obtained by crushing the ingot obtained in this way to obtain magnetic powder, which is then formed to a desired size.

[0031] As described above, the grain boundary phase contains a mixture of phases of various compositions. When the main phase is nanocrystalline, the phases in the grain boundary phase are mostly amorphous phases with unclear crystalline structures. When the phase has a clear crystalline structure, it is preferable that it has an RFe2 type crystalline structure, and its proportion is preferably 1.0 volume% or more, 1.2 volume% or more, or 1.4 volume% or more, and preferably 3.0 volume% or less, 2.8 volume% or less, or 2.6 volume% or less. This results in a small decrease in coercivity with increasing temperature and prevents the coercivity at room temperature from becoming excessively high. The reason for this is that the phase having an RFe2 "type" crystalline structure may contain elements other than R and Fe, especially metallic elements, in substitutional and / or interstitial forms.

[0032] The volume fraction of the phase having an RFe2-type crystal structure is determined by performing Rietveld analysis on the X-ray diffraction pattern of the rare earth magnet of this disclosure to find the volume fraction of the phase having an RFe2-type crystal structure. In the rare earth magnet of this disclosure, assuming that all phases other than the main phase are grain boundary phases, the volume fraction of the grain boundary phases is calculated. Then, when the volume ratio of the phase having an RFe2-type crystal structure to the grain boundary phases is calculated from (volume fraction of the phase having an RFe2-type crystal structure) / (volume fraction of the grain boundary phases), it is preferable that this ratio is 0.60 or less, and more preferably 0.40 or less. This makes it easier to further reduce the decrease in coercivity with increasing temperature.

[0033] The overall composition of the rare earth magnets disclosed herein is the main phase (R2Fe) as previously described. 14 This refers to the total composition of all phases (B) and grain boundary phases. If a modifier is impregnated into the main phase and grain boundary phases, the composition of the rare earth magnet in this disclosure also includes the composition of the modifier. The diffusion and impregnation of the modifier will be described in detail in "Manufacturing Method". In the overall composition of the rare earth magnet in this disclosure, at least a portion of R is specified, and a portion of Fe is replaced with a predetermined proportion of Co. R and Co will be described below.

[0034] <R> In the rare earth magnets of this disclosure, at least La and Ce are selected as R. This avoids the excessively high coercivity at room temperature, as described above, and improves desorption magnetism at room temperature. "At least La and Ce are selected" means that La and Ce are essential as R, and other rare earth elements other than La and Ce may be selected. Although not bound by theory, it is thought that the coexistence of La and Co is effective in promoting the phase having the RFe2 type crystal structure in the grain boundary phase as described above. For this reason, in the rare earth magnets of this disclosure, some of the Fe is replaced with Co, and La and Co coexist. However, if all of R is La, then R2Fe 14 Because maintaining phase B is difficult, the rare earth magnets of this disclosure require both La and Ce as R.

[0035] <Co> In the rare earth magnets of this disclosure, a portion of the Fe is replaced with Co. The proportion of Co that is substituted is 0.20 to 0.25 in molar ratio with respect to the total amount of Fe and Co.

[0036] If the molar ratio of Co to the total amount of Fe is 0.20 or higher, the magnetic anisotropy at high temperatures can be favorably maintained, and as a result, the decrease in coercivity with increasing temperature can be reduced.

[0037] On the other hand, if the molar ratio of Co to the total Fe is 0.25 or less, the phase having an RFe2-type crystal structure is less likely to be formed in excess, and as a result, an excessive decrease in coercivity at room temperature can be avoided. From this viewpoint, the molar ratio of Co to the total Fe may be 0.24 or less, 0.23 or less, 0.22 or less, or 0.21 or less.

[0038] The overall composition of the rare earth magnets of this disclosure is not particularly limited, as long as it comprises a main phase and grain boundary phases that satisfy the above requirements, and R, Fe, and Co satisfy the above requirements. However, the overall composition of the rare earth magnets of this disclosure is typically expressed as follows:

[0039] <Overall composition> The overall composition of the rare earth magnet of this disclosure will now be described. As shown in Figure 1, the rare earth magnet 100 of this disclosure comprises a main phase 10 and a grain boundary phase 20. Therefore, the overall composition of the rare earth magnet 100 of this disclosure refers to the total composition of the main phase 10 and the grain boundary phase 20 combined. If a modifier is diffused and permeated into the main phase and the grain boundary phase, the composition of the rare earth magnet of this disclosure will also include the composition of the modifier. The diffusion and permeation of the modifier will be described in detail in "Manufacturing Method".

[0040] The overall composition of the rare earth magnets of this disclosure is typically given by the formula (R) in molar ratio. 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M1 v ·(R 2 (1-s) M 2 s ) t It can be expressed as follows. In this equation, when t is 0, that is, equation (R 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v This represents the overall composition when the modifier is not diffused or permeated. Formula (R 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v ·(R 2 (1-s) M 2 s ) t This represents the overall composition when the modifier is diffused and permeated. In this formula, the first part (R 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v This represents the composition derived from the sintered body (rare earth magnet precursor) before the modifier diffuses and permeates, and the latter part (R 2 (1-s) M 2 s ) t This represents the composition derived from the modifier.

[0041] When the modifier is diffused and permeated, a sintered body of 100 moles is used as a rare earth magnet precursor, and t moles of the modifier are diffused and permeated into its interior. This yields (100 + t) moles of the rare earth magnet of this disclosure.

[0042] An expression representing the overall composition of the rare earth magnet of the present disclosure, where R 1 , the total of La and Ce is y mole parts, the total of Fe and Co is (100 - y - w - v) mole parts, B is w mole parts, and M 1 is v mole parts. Therefore, the sum of these is y mole parts + (100 - y - w - v) mole parts + w mole parts + v mole parts = 100 mole parts. The total of R 2 and M 2 is t mole parts.

[0043] In the above formula, R 1 (1-x1-x2) La x1 Ce x2 means that there is (1 - x1 - x2) of R in molar ratio with respect to the total of R, La, and Ce, there is x1 of La, and there is x2 of Ce. Similarly, in the above formula, Fe 1 Co 1 means that there is (1 - z) of Fe in molar ratio with respect to the total of Fe and Co, and there is z of Co. Also, similarly, in the above formula, R (1-z) z M 2 (1-s) 2 represents that there is (1 - s) of R in molar ratio with respect to the total of R s and M 2 2 2 and there is s of M 1 1 2 1 2 2

[0044] In the above formula, R 1 and R 2 are one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho. Nd is neodymium, Pr is praseodymium, Gd is gadolinium, Tb is terbium, Dy is dysprosium, and Ho is holmium. Fe is iron. Co is cobalt. B is boron. M 1This refers to one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, as well as unavoidable impurity elements. Ga is gallium, Al is aluminum, Cu is copper, Au is gold, Ag is silver, Zn is zinc, In is indium, and Mn is manganese. 2 R 2 These are metallic elements other than rare earth elements that alloy with other elements, as well as unavoidable impurity elements.

[0045] In this specification, unless otherwise specified, rare earth elements are the 17 elements Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Of these, unless otherwise specified, Sc, Y, La, and Ce are light rare earth elements. Unless otherwise specified, Pr, Nd, Pm, Sm, and Eu are medium rare earth elements. Unless otherwise specified, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu are heavy rare earth elements. Generally, heavy rare earth elements are highly rare, and light rare earth elements are less rare. The rarity of medium rare earth elements is between that of heavy and light rare earth elements. Note that Sc stands for scandium, Y for yttrium, La for lanthanum, Ce for cerium, Pr for praseodymium, Nd for neodymium, Pm for promethium, Sm for samarium, Eu for eurobium, Gd for gadolinium, Tb for terbium, Dy for dysprosium, Ho for holmium, Er for erbium, Tm for thulium, Yb for ytterbium, and Lu for lutetium.

[0046] The constituent elements of the rare earth magnet of this disclosure, as represented by the formula described above, will be explained below.

[0047] <R 1 > As mentioned above, R 1 R is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho. 1 The main phase (R2Fe) is present in this disclosure, along with La and Ce, which are essential as R in the rare earth magnet. 14 A phase having a type B crystal structure (hereinafter referred to as "R2Fe") 14It is sometimes called "phase B". )) is a constituent element. From the perspective of the balance between remanent magnetization, coercivity and price, R 1 It is preferable that R is one or more elements selected from the group consisting of Nd and Pr. 1 Therefore, when Nd and Pr are to be used together, didymium may be used.

[0048] <La and Ce> La is an essential element selected as R in the rare earth magnets of this disclosure. La and Ce, together with Co, produce the effects and properties described above.

[0049] <R 1 Molar ratio of La and Ce〉 In the above equation, R 1 The molar ratio of La and Ce is R 1 (1-x1-x2) La x1 Ce x2 It can be expressed as follows. In the rare earth magnet of this disclosure, as described above, La and Ce are essential. Since both La and Ce coexist, x1 and x2 satisfy 0.01≦x1≦0.99 and 0.01≦x2≦0.99. These lower limits mean that in order to achieve the above-mentioned effects and benefits, both La and Ce must be present in some amount as R, and represent the minimum molar ratio required for the above-mentioned effects and benefits to be observed. The upper limits mean that neither La nor Ce should be selected as the entirety of R, and represent the maximum molar ratio at which neither is selected as the entirety of R. Furthermore, it is natural that the sum of x1 and x2 does not exceed 1.00, and since the lower limits of x1 and x2 are as described above, it satisfies 0.02≦x1+x2≦1.

[0050] To more favorably enjoy the effects and benefits described above, x1 is preferably 0.20 or higher, 0.25 or higher, or 0.27 or higher, and preferably 0.45 or lower, 0.40 or lower, or 0.35 or lower. Similarly, x2 is preferably 0.45 or higher, 0.50 or higher, or 0.52 or higher, and preferably 0.75 or lower, 0.70 or lower, or 0.65 or lower. These preferred ranges may be satisfied for either x1 or x2.

[0051] <R 1 Total content of La and Ce〉 In the above equation, R 1 The total content of , La, and Ce is expressed as y, satisfying 12.0 ≤ y ≤ 20.0. The value of y is the content of the rare earth magnets in this disclosure when the modifier is not diffused or permeated, and corresponds to mole percent (atomic percent).

[0052] If y is 12.0 or higher, a large amount of αFe phase will not be formed in the grain boundary phase, and a sufficient amount of the main phase (R2Fe) will be formed. 14 A B phase can be obtained. From this viewpoint, y may be 12.4 or greater, 12.8 or greater, 13.0 or greater, 13.2 or greater, 13.4 or greater, 13.6 or greater, or 14.0 or greater. On the other hand, if y is 20.0 or less, there will be no excess grain boundary phase. From this viewpoint, y may be 19.0 or less, 18.0 or less, 17.0 or less, 16.0 or less, or 15.0 or less.

[0053] B is the main phase (R2Fe) in Figure 1. 14 It constitutes phase B and influences the relative proportions of the main phase and grain boundary phase.

[0054] The content of B is represented by w in the above formula. The value of w is the content of B in the rare earth magnet of this disclosure when the modifier is not diffused and permeated, and corresponds to mole percent (atomic percent). If w is 20.0 or less, a rare earth magnet can be obtained in which the main phase 10 and grain boundary phase 20 are appropriately present. From this viewpoint, w may be 18.0 or less, 16.0 or less, 14.0 or less, 12.0 or less, 10.0 or less, 8.0 or less, 6.0 or less, or 5.9 or less. On the other hand, if w is 5.0 or more, Th2Zn 17 Type and / or Th2Ni 17 It is unlikely that a large amount of phase with this type of crystal structure will be generated, and as a result, R2Fe 14 The formation of phase B is less likely to be inhibited. From this perspective, w may be 5.2 or higher, 5.4 or higher, 5.5 or higher, 5.7 or higher, or 5.8 or higher.

[0055] <M 1 > M 1 M is an element that can be included in a range that does not impair the properties of the rare earth magnets of this disclosure. 1 It may contain unavoidable impurity elements. In this specification, unavoidable impurity elements refer to impurity elements contained in the raw materials of rare earth magnets, or impurity elements that are introduced during the manufacturing process, etc., whose inclusion cannot be avoided, or whose avoidance would lead to a significant increase in manufacturing costs. Impurity elements introduced during the manufacturing process include elements that are included to the extent that they do not affect the magnetic properties, for manufacturing reasons. In addition, unavoidable impurity elements include R 1 It includes rare earth elements other than those selected as La and Ce, which are inevitably mixed in for the reasons mentioned above.

[0056] Elements M that can be included in this disclosure without impairing the effects of the rare earth magnet and its manufacturing method. 1 Examples include one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn. These elements are M 1As long as these elements are present below the upper limit of their content, they do not substantially affect the magnetic properties. Therefore, these elements may be treated the same as unavoidable impurity elements. In addition to these elements, M 1 It may contain unavoidable impurity elements. 1 Preferably, the elements are one or more selected from the group consisting of Ga, Al, and Cu, as well as unavoidable impurity elements.

[0057] In the above equation, M 1 The content ratio is represented by v. The value of v is the content ratio relative to the rare earth magnet of this disclosure that has not been diffused or permeated by the modifier, and corresponds to mol% (atomic%). If the value of v is 2.0 or less, the magnetic properties of the rare earth magnet of this disclosure will not be impaired. From this viewpoint, v may be 1.5 or less, 1.0 or less, 0.65 or less, 0.6 or less, or 0.5 or less.

[0058] M 1 Since it is impossible to completely eliminate Ga, Al, Cu, Au, Ag, Zn, In, and Mn, as well as unavoidable impurity elements, a lower limit of v of 0.05, 0.1, or 0.2 is practically acceptable.

[0059] <Fe and Co> Fe is R 1 , along with La, Ce, and B, the main phase (R2Fe 14 It is the main component constituting phase B. In the rare earth magnet of this disclosure, a portion of Fe is replaced with Co, and as described above, the desired function and effect are achieved when the molar ratio of Co to the total of Fe and Co is within a predetermined range.

[0060] <Molar ratio of Fe and Co> In the above equation, the molar ratio of Co to the total of Fe and Co is: (1-z) Co z This is expressed as follows. Therefore, for the specified range mentioned above, it means that z is 0.20 or greater, and 0.25 or less, 0.24 or less, 0.23 or less, 0.22 or less, or 0.21 or less.

[0061] <Total content of Fe and Co> The total percentage of Fe and Co is as explained earlier in R 1 , La, Ce, B, and M 1 This is the remainder and is represented as (100-ywv). As described above, the values ​​of y, w, and v are the content ratios relative to the rare earth magnet of this disclosure that has not been diffused or permeated by the modifier, so (100-ywv) corresponds to mole percent (atomic percent). When y, w, and v are set to the ranges described above, the main phase 10 and grain boundary phase 20 shown in Figure 1 are obtained.

[0062] <R 2 > R 2 is an element derived from the modifier. The modifier diffuses and penetrates into the interior of the sintered body of the magnetic strip or magnetic flake (the rare earth magnet of this disclosure when the modifier does not diffuse and penetrate). The molten modifier diffuses and penetrates through the grain boundary phase 20 in Figure 1.

[0063] R 2 Examples include one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho. 2 When Nd and Pr coexist, didymium may be used. The modifier improves coercivity by magnetically separating the main phases. 2 Among these, selecting heavy rare earth elements can result in excessively high coercivity at room temperature. Therefore, R 2 This is one or more elements selected from the group consisting of Nd and Pr, with Nd being particularly preferred.

[0064] <M 2 > M 2 R 2 These are metallic elements other than rare earth elements that alloy with the metal, and unavoidable impurity elements. Typically, M 2 R 2 (1-s) M 2 s The melting point of R 2 These are alloying elements and unavoidable impurity elements that lower the melting point below that of the element.2 Examples include one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, as well as unavoidable impurity elements. 2 (1-s) M 2 s From the perspective of the decrease in melting point, M 2 Preferably, one or more elements selected from the group consisting of Al and Cu are used, with Cu being particularly preferred. Unavoidable impurity elements refer to impurity elements contained in the raw materials, or impurity elements that are introduced during the manufacturing process, etc., whose inclusion cannot be avoided, or whose avoidance would lead to a significant increase in manufacturing costs. Impurity elements introduced during the manufacturing process include elements that are included to the extent that they do not affect the magnetic properties due to manufacturing considerations. In addition, unavoidable impurity elements include R 2 In addition to the rare earth elements selected as such, it also includes rare earth elements that are inevitably mixed in for the reasons mentioned above.

[0065] <R 2 and M 2 Mole ratio of R 2 and M 2 is, formula R 2 (1-s) M 2 s An alloy having a composition with a molar ratio represented by is formed, and the modifier contains this alloy. Furthermore, s satisfies 0.05 ≤ s ≤ 0.40.

[0066] If s is 0.05 or higher, the molten modifier can be diffused into the interior of the sintered body (the rare earth magnet of this disclosure when the modifier is not diffused into it) at a temperature that avoids coarsening of the main phase. From this viewpoint, s is preferably 0.10 or higher, and more preferably 0.15 or higher. On the other hand, if s is 0.40 or lower, after the modifier has diffused into the interior of the sintered body (the rare earth magnet of this disclosure when the modifier is not diffused into it), M remains in the grain boundary phase of the rare earth magnet of this disclosure. 2By suppressing the content of [substance name], it contributes to suppressing the decrease in remanent magnetization. From this viewpoint, s may be 0.35 or less, 0.30 or less, 0.25 or less, 0.20 or less, or 0.18 or less.

[0067] <Molar ratio of elements derived from the sintered body to elements derived from the modifier> As described above, when the modifier is diffused and permeated, the overall composition of the rare earth magnet of this disclosure is given by formula (R 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v ·(R 2 (1-s) M 2 s ) t It is expressed as follows: In this formula, the first part (R 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v This represents the composition derived from the sintered body (rare earth magnet precursor) before the modifier diffuses and permeates, and the latter part (R 2 (1-s) M 2 s ) t This represents the composition derived from the modifier.

[0068] In the above equation, the ratio of the modifier to 100 moles of sintered body is t moles. That is, when t moles of the modifier are diffused into 100 moles of sintered body, 100 moles + t moles of the rare earth magnet of the present disclosure are obtained. In other words, for a 100 mol% (100 atomic%) sintered body, the rare earth magnet of the present disclosure is (100+t) mol% ((100+t) atomic%).

[0069] A value of 0 for t means that the modifier has not diffused or permeated in the rare earth magnet of this disclosure. If the modifier has diffused or permeated, a value of 0.1 or greater can substantially be recognized as having the effect of magnetically separating the main phase and improving coercivity. From this viewpoint, t may be 0.5 or greater, 1.0 or greater, 2.0 or greater, 3.0 or greater, 4.0 or greater, 5.0 or greater, or 0.6 or greater. On the other hand, if t is 20.0 or less, M remains in the grain boundary phase of the rare earth magnet of this disclosure. 2 The content of is suppressed to suppress the decrease in remanent magnetization. From this viewpoint, t may be 18.0 or less, 16.0 or less, 14.0 or less, 13.0 or less, 12.0 or less, 11.0 or less, 10.0 or less, or 9.0 or less, 8.0 or less, or 7.0 or less.

[0070] To summarize the explanation so far, the overall composition of the rare earth magnets in this disclosure in terms of molar ratio is given by formula (R 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v ·(R 2 (1-s) M 2 s ) t It is expressed as follows: However, R 1 and R 2 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho, and M 1 This is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, as well as unavoidable impurity elements, M 2 R 2 These are metallic elements other than rare earth elements that alloy with the metal, and unavoidable impurity elements. Furthermore, they satisfy the following conditions: 0.01≦x1≦0.99, 0.01≦x2≦0.99, 0.02≦x1+x2≦1, 12.0≦y≦20.0, 0.20≦z≦0.25, 5.0≦w≦20.0, 0≦v≦2.0, 0.05≦s≦0.40, and 0≦t≦20.0.

[0071] 《Manufacturing method》 Next, the method for manufacturing the rare earth magnets of this disclosure will be described.

[0072] The method for manufacturing rare earth magnets according to this disclosure includes the steps of preparing molten metal, cooling the molten metal, and sintering. The resulting sintered body may be used as the rare earth magnet according to this disclosure, or a modifying agent may be diffused and impregnated into the sintered body to form the rare earth magnet according to this disclosure. Optionally, a step for imparting anisotropy may also be included. Each of these steps will be described below.

[0073] <Preparing the molten metal> Formula in molar ratio (R 1 (1-x1-x2) La x1 Ce x2 ) y (Fe (1-z) Co z ) (100-y-w-v) B w M 1 v Prepare a molten metal having the composition represented by the formula. In this formula, R 1 La, Ce, Fe, Co, B, and M 1 As for x1, x2, y, z, w, and v, they are as explained in "Rare Earth Magnets". For elements that may be depleted in subsequent processes, this depletion may be taken into consideration.

[0074] <Molten metal cooling> The molten metal having the above composition is rapidly cooled or rapidly cooled. In this specification, unless otherwise specified, rapidly cooled means 5 × 10 5 °C / second or higher, 1 × 10 6 °C / second or higher, or 5 × 10 6 °C / second or higher, and 5 × 10 7 °C / second or less or 1 × 10⁻⁶ 7 This means cooling at a rate of 1°C / second or less. When a molten metal having the above composition is rapidly cooled, a magnetic ribbon or magnetic flake having a nanocrystalline main phase is obtained. Rapid cooling means 1 × 10⁻⁶ 0 °C / second or higher, 5 × 10 0 °C / sec or higher, 1 × 10 °C / sec or higher, 5 × 10 °C / sec or higher, or 1 × 10 2°C / second or higher, and 1 × 10⁻⁶ 4 ℃ / sec or less, 5×10 3 ℃ / sec or less, 1×10 3 °C / second or less, or 5°C × 10 2 This means cooling at a rate of °C / second or less. When molten metal having the above composition is rapidly cooled, a magnetic ribbon or magnetic flake having a main phase with an average particle size of 1 to 10 μm is obtained.

[0075] The method of ultra-rapid or rapid cooling of the molten metal at the aforementioned rates is not particularly limited, but typically, the liquid quenching method is applied for ultra-rapid cooling, and the strip casting method is applied for rapid cooling. Ultra-rapid cooling can be achieved by rotating the cooling rolls in the strip casting method at a higher speed than in the rapid cooling method. The liquid quenching method and the strip casting method will be briefly explained with reference to the drawings.

[0076] Figure 2 is a schematic diagram illustrating a cooling device used in the liquid rapid cooling method.

[0077] The liquid quenching device 50 includes an injection nozzle 51, a heater 52, and a cooling roll 53. The injection nozzle 51 is installed facing the outer surface of the cooling roll 53. Molten metal is injected from the injection nozzle 51 onto the outer surface of the cooling roll 53, which rotates at high speed, and the molten metal is cooled to obtain a magnetic strip 54. Depending on the rotation speed of the cooling roll and / or the injection conditions, a magnetic flake 55 can be obtained. Compared to the strip casting device described later, the liquid quenching device 50 can ultra-rapidly cool the molten metal because it is injected directly from the injection nozzle 51 onto the outer surface of the cooling roll 53.

[0078] Molten metal may be supplied to the injection nozzle 51, or raw materials for the molten metal may be charged into the injection nozzle 51 and melted by the heater 52.

[0079] The cooling roll 53 is made of a material with high thermal conductivity, such as copper or chromium, and its surface is plated with chromium or the like to prevent erosion from high-temperature molten metal. The cooling roll 53 can be rotated in the direction of the arrow at a predetermined rotational speed by a drive device (not shown).

[0080] To rapidly cool the molten metal at the above-mentioned rate, the peripheral speed of the cooling roll 53 may be, for example, 15 to 30 m / second. When rapidly cooling the molten metal using the liquid quenching method, an inert gas atmosphere is preferred to prevent oxidation of the molten metal, etc. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0081] The temperature of the molten metal when it is sprayed from the injection nozzle 51 onto the outer surface of the cooling roll 53 may be, for example, 1350°C or higher, 1400°C or higher, or 1450°C or higher, and may be 1600°C or lower, 1550°C or lower, or 1500°C or lower.

[0082] Figure 3 is a schematic diagram illustrating a cooling device used in the strip casting method.

[0083] The strip casting apparatus 70 comprises a melting furnace 71, a tundish 73, and a cooling roll 74. In the melting furnace 71, the raw materials are melted to prepare molten metal 72 having the above-described composition. The molten metal 72 is supplied to the tundish 73 at a constant rate. The molten metal 72 supplied to the tundish 73 is then supplied to the cooling roll 74 by its own weight from the end of the tundish 73.

[0084] The tundish 73 is made of ceramics or the like and can temporarily store the molten metal 72 that is continuously supplied from the melting furnace 71 at a predetermined flow rate, and can straighten the flow of the molten metal 72 to the cooling roll 74. The tundish 73 also has the function of adjusting the temperature of the molten metal 72 just before it reaches the cooling roll 74.

[0085] The cooling roll 74 is made of a highly thermally conductive material such as copper or chromium, and its surface is plated with chromium or the like to prevent erosion from high-temperature molten metal. The cooling roll 74 can be rotated at a predetermined rotational speed in the direction of the arrow by a drive device (not shown).

[0086] The peripheral speed of the cooling roll 74 may be, for example, 0.5 to 3.0 m / s when rapidly cooling the molten metal, and for example, 20 to 40 m / s when extremely rapidly cooling the molten metal.

[0087] The temperature of the molten metal supplied from the end of the tundish 73 to the cooling roll 74 may be, for example, 1350°C or higher, 1400°C or higher, or 1450°C or higher, and may be 1600°C or lower, 1550°C or lower, or 1500°C or lower.

[0088] The molten metal 72, cooled and solidified on the outer circumference of the cooling roll 74, becomes a magnetic alloy 75, which detaches from the cooling roll 74 and is recovered by a recovery device (not shown). The magnetic alloy 75 typically takes the form of a thin strip or thin flake. When cooling the molten metal using the strip casting method, an inert gas atmosphere is preferred to prevent oxidation of the molten metal, etc. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0089] <Sintering> A sintered body is obtained by sintering a magnetic strip or magnetic flake. Known methods and conditions can be applied to the sintering. Sintering can be broadly classified into pressure sintering and non-pressure sintering. Compared to non-pressure sintering, pressure sintering allows for sintering of magnetic strips or flakes at relatively low temperatures and in a short time by applying pressure. Therefore, pressure sintering is typically applied to sintering magnetic strips or flakes having a nanocrystalline main phase. This allows for obtaining a sintered body without coarsening the nanocrystalline main phase. Non-pressure sintering requires sintering the magnetic strip or flake at high temperatures for a long time. Therefore, non-pressure sintering is typically applied to sintering magnetic strips or flakes having a main phase with an average grain size of 1 to 10 μm. Compared to magnetic strips or flakes with a nanocrystalline main phase, magnetic strips or flakes with a main phase having an average grain size of 1 to 10 μm often have harmful phases in the grain boundary phase that negatively affect magnetism because the molten metal is cooled at a slow rate. By sintering a magnetic ribbon or magnetic flake at a high temperature for a long period of time, such harmful phases can be favorably dispersed in the grain boundary phase.

[0090] The sintering conditions should be determined appropriately so that the main phase does not coarseen and a good sintered body density is obtained. The sintering conditions are described below separately for pressurized sintering and non-pressurized sintering.

[0091] The pressurized sintering temperature may be, for example, 470°C or higher, 500°C or higher, 550°C or higher, or 600°C or higher, and may be 750°C or lower, 700°C or lower, 670°C or lower, or 650°C or lower. The pressurized sintering pressure may be, for example, 50 MPa or higher, 100 MPa or higher, 150 MPa or higher, 200 MPa or higher, or 350 MPa or higher, and may be 600 MPa or lower, 500 MPa or lower, 450 MPa or lower, or 400 MPa or lower. The pressurized sintering time may be, for example, 0.5 minutes or more, 1 minute or more, 5 minutes or more, 10 minutes or more, 15 minutes or more, 30 minutes or more, or 60 minutes or more, and may be 150 minutes or less, 120 minutes or less, or 90 minutes or less. After the pressurized sintering is completed, it is preferable to remove the sintered body from the sintering mold and cool the sintered body quickly. This can suppress the formation of phases other than the desired phase. The cooling rate may be, for example, 10°C / min or more, 30°C / min or more, or 50°C / min or more, and may be 1000°C / min or less, 800°C / min or less, 600°C / min or less, 400°C / min or less, 200°C / min or less, 100°C / min or less, 80°C / min or less, or 70°C / min or less. In order to suppress oxidation of the magnetic strip or magnetic flake during pressurized sintering, an inert gas atmosphere is preferred for the pressurized sintering atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0092] Magnetic strips or flakes having a nanocrystalline main phase are obtained by ultra-rapid cooling of molten metal. Because the magnetic strips or flakes obtained by ultra-rapid cooling are very thin, they are crushed when charged into a pressure sintering mold and / or during the pressure sintering operation. However, the magnetic strips or flakes may be crushed beforehand before pressure sintering. For crushing, for example, pin mills, cutter mills, ball mills, and jet mills can be used. These may be used in combination. Alternatively, the magnetic strips or flakes, or the magnetic powder obtained by crushing them, may be pre-compressed and molded to form a compact before pressure sintering, and this compact may be pressure sintered.

[0093] The no-pressure sintering temperature may be, for example, 900°C or higher, 950°C or higher, or 1000°C or higher, and may be 1100°C or lower, 1050°C or lower, or 1040°C or lower. The no-pressure sintering time may be, for example, 1 hour or more, 2 hours or more, 3 hours or more, or 4 hours or more, and may be 24 hours or less, 18 hours or less, 12 hours or less, or 6 hours or less.

[0094] Magnetic strips or flakes having a main phase with an average particle size of 1 to 10 μm are obtained by rapidly cooling molten metal. Compared to magnetic strips or flakes obtained by ultra-rapid cooling, those obtained by rapid cooling are relatively thicker. Therefore, it is typical to form a compact by compressing a magnetic powder obtained by pre-grinding magnetic strips or flakes, and then sintering this compact under no pressure. For grinding, for example, pin mills, cutter mills, ball mills, and jet mills can be used. These may also be used in combination. To suppress oxidation of the compact during unpressurized sintering, an inert gas atmosphere is preferred for the unpressurized sintering atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0095] <Anisotropy> To improve residual magnetization, it is preferable to optionally include a process to impart anisotropy. Well-known methods can be applied to impart anisotropy. When the main phase is nanocrystalline, it is typical to hot-form the sintered body. When the average particle size of the main phase is 1 to 10 μm, it is typical to obtain a compact by compressing a magnetic powder, which is obtained by pre-pulverizing magnetic strips or magnetic flakes, in a magnetic field (hereinafter sometimes referred to as "magnetic field forming"). Hot-formation and magnetic field forming will be described below.

[0096] <Hot plastic working> The sintered body obtained by pressure sintering is subjected to hot plastic deformation. This makes it possible to impart anisotropy to the rare earth magnet of this disclosure. The conditions for hot plastic deformation can be appropriately determined so as to impart anisotropy to the sintered body while avoiding coarsening of the main phase.

[0097] The hot plastic working temperature may be, for example, 750°C or higher, 770°C or higher, or 790°C or higher, and may be 850°C or lower, 830°C or lower, or 800°C or lower. The hot plastic working pressure may be, for example, 30 MPa or higher, 50 MPa or higher, 100 MPa, 200 MPa or higher, 500 MPa or higher, 700 MPa or higher, or 900 MPa or higher, and may be 3000 MPa or lower, 2500 MPa or lower, 2000 MPa or lower, 1500 MPa or lower, or 1000 MPa or lower. The reduction ratio may be 10% or higher, 30% or higher, 50% or higher, or 60% or higher, and may be 80% or lower, 75% or lower, 70% or lower, or 65% or lower. The strain rate during hot plastic deformation may be 0.01 / s or more, 0.1 / s or more, 1.0 / s or more, or 3.0 / s or more, and may be 15.0 / s or less, 10.0 / s or less, or 5.0 / s or less.

[0098] After the completion of hot plastic deformation, it is preferable to cool the sintered body rapidly. This helps to avoid coarsening of the main phase and suppress the formation of harmful phases that adversely affect magnetism. The cooling rate may be, for example, 10°C / min or more, 30°C / min or more, or 50°C / min or more, and may be 1000°C / min or less, 800°C / min or less, 600°C / min or less, 400°C / min or less, 300°C / min or less, 200°C / min or less, 100°C / min or less, or 70°C / min or less. To suppress oxidation of the sintered body during hot plastic deformation, an inert gas atmosphere is preferred for the hot plastic deformation atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0099] <Magnetic field forming> A magnetic strip or magnetic flake, preferably a magnetic powder obtained by crushing these, is compressed and molded in a magnetic field to obtain a compacted body. This imparts anisotropy to the rare earth magnet of this disclosure and also contributes to improving the density of the sintered body. The magnetic field molding pressure may be, for example, 50 MPa or more, 100 MPa or more, 200 MPa or more, or 300 MPa or more, and may be 1000 MPa or less, 800 MPa or less, or 600 MPa or less. In order to impart anisotropy to the sintered body, the magnetic powder may be compacted while a magnetic field is applied. The applied magnetic field may be 0.1 T or more, 0.5 T or more, 1.0 T or more, 1.5 T or more, or 2.0 T or more, and may be 10.0 T or less, 8.0 T or less, 6.0 T or less, or 4.0 T or less.

[0100] <Diffusion and Penetration> The sintered body obtained by pressure sintering or non-pressure sintering may optionally be diffused and impregnated with a modifying agent. This can advantageously improve the coercivity of the rare earth magnet of this disclosure, particularly its coercivity at high temperatures.

[0101] The diffusion and penetration of the modifier involves preparing the modifier and then diffusing and penetrating it into the sintered body. When the overall composition of the rare earth magnet of this disclosure is expressed by the above formula, the formula R in molar ratio is expressed by 2 (1-s) M 2 s Prepare a modifier having the composition represented by . In the formula representing the composition of the modifier, R 2 and M 2 As for s, it is as explained in "Rare Earth Magnets".

[0102] Methods for preparing the modifier include, for example, obtaining thin strips and / or flakes from molten metal having the composition of the modifier using a liquid quenching method or a strip casting method. In these methods, the molten metal is ultra-rapidly cooled or rapidly cooled, resulting in less segregation in the modifier, which is preferable. Other methods for preparing the modifier include, for example, casting molten metal having the composition of the modifier into a mold such as a book mold. This method allows for the relatively simple acquisition of a large amount of modifier. To reduce segregation of the modifier, it is preferable that the book mold be made of a material with high thermal conductivity. It is also preferable to homogenize the cast material through heat treatment to suppress segregation. Furthermore, another method for preparing the modifier involves charging the raw materials of the modifier into a container, arc melting the raw materials in the container, and cooling the molten material to obtain an ingot. In this method, the modifier can be obtained relatively easily even when the melting point of the raw materials is high. From the viewpoint of reducing segregation of the modifier, it is preferable to homogenize the ingot through heat treatment.

[0103] The prepared modifying agent is diffused and permeated into the sintered body. When the sintered body is hot-plasticly formed, typically the modifying agent is diffused and permeated into the sintered body after the hot-plastic formation. That is, the modifying agent may be diffused and permeated into the sintered body before hot-plastic formation, or it may be diffused and permeated into the sintered body after hot-plastic formation. In the following explanation of the diffusion and permeation of the modifying agent, "sintered body" includes the sintered body after hot-plastic formation.

[0104] A typical method of diffusion penetration involves bringing a modifying material into contact with a sintered body to obtain a contact body, and then heating this contact body to diffuse and penetrate the molten modifying material into the interior of the sintered body. The molten modifying material diffuses and penetrates through the grain boundary phase 20 shown in Figure 1. The molten modifying material then solidifies in the grain boundary phase 20, magnetically separating the main phases 10, which advantageously improves the coercivity, especially the coercivity at high temperatures.

[0105] The form of the contacting body is not particularly limited as long as the modifying material is in contact with the sintered body. Examples of the form of the contacting body include a form in which a thin strip and / or flake of the modifying material obtained by liquid quenching and / or strip casting is brought into contact with the sintered body. Other examples of the form of the contacting body include a form in which a powder of the modifying material obtained by crushing a thin strip and / or flake, book mold material, or arc melting and solidification material obtained by liquid quenching and / or strip casting is brought into contact with the sintered body.

[0106] The diffusion and penetration conditions are not particularly limited, as long as they allow the modifying agent to diffuse and penetrate into the interior of the sintered body without causing the main phase to coarseen and suppressing the formation of harmful phases that adversely affect magnetism.

[0107] The diffusion and penetration temperature may be, for example, 550°C or higher, 600°C or higher, or 650°C or higher, and may be 750°C or lower, 740°C or lower, 730°C or lower, 720°C or lower, 710°C or lower, or 700°C or lower. The diffusion and penetration time may be 30 minutes or more, 60 minutes or more, 90 minutes or more, or 120 minutes or more, and may be 300 minutes or less, 240 minutes or less, 210 minutes or less, 180 minutes or less, 165 minutes or less, or 150 minutes or less. After the diffusion and penetration of the modifier, it is preferable to cool the sintered body rapidly. This can suppress the generation of harmful phases that adversely affect magnetism. The cooling rate may be, for example, 1°C / min or more, 10°C / min or more, 30°C / min or more, or 50°C / min or more, and may be 1000°C / min or less, 800°C / min or less, 600°C / min or less, 400°C / min or less, 300°C / min or less, 200°C / min or less, 100°C / min or less, or 70°C / min or less. To suppress oxidation of the sintered body during diffusion and penetration, an inert gas atmosphere is preferred for the diffusion and penetration atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0108] When the overall composition of the rare earth magnet of this disclosure is expressed by the above formula, during the diffusion and penetration of the modifier, t moles of the modifier are brought into contact with 100 moles of the sintered body. The value of t is as explained in "Rare Earth Magnets".

[0109] Since the modifying agent is diffused and permeated under conditions that do not coarseen the main phase of the sintered body, the average particle size of the main phase before the diffusion and permeation of the modifying agent is substantially within the same size range as the average particle size of the main phase after the diffusion and permeation of the modifying agent. The average particle size and crystal structure of the main phase are as explained in "Rare Earth Magnets".

[0110] During the diffusion and penetration of the modifier, an inert gas atmosphere is preferred in order to suppress oxidation of the sintered body and the modifier. An inert gas atmosphere includes a nitrogen gas atmosphere.

[0111] <Transformation> In addition to what has been described above, the rare earth magnets of this disclosure can be modified in various ways within the scope of the claims. [Examples]

[0112] The rare earth magnets of this disclosure will be described in more detail below with reference to examples and comparative examples. However, the rare earth magnets of this disclosure are not limited to the conditions used in the following examples.

[0113] Sample preparation The samples for Examples 1-2 and Comparative Examples 1-7 were prepared using the following procedure.

[0114] <Preparation of samples for Examples 1-2 and Comparative Examples 3-7> Liquid quenching material (magnetic tape) with the composition shown in Table 1-1 was prepared. A liquid quenching apparatus 50 shown in Figure 2 was used for the preparation. The peripheral speed of the cooling roll 53 was 30 m / sec, and the cooling rate of the molten metal was 10 6 The temperature was °C / second. After coarsely grinding this liquid quenching material, it was pressure-sintered. The temperature during pressure-sintering was 600 °C, the pressure was 400 MPa, and the pressure-sintering time was 5 minutes. Table 1-1 also shows x1, x2, and z when the overall composition of the rare-earth magnet of this disclosure is expressed by the above formula. In Table 1-1, "bal" means the remainder.

[0115] After pressure sintering, the material was cooled to 400°C at a rate of 100°C / min to obtain a sintered body. This sintered body was then subjected to hot plastic deformation. The hot plastic deformation temperature was 750°C, the hot plastic deformation pressure was a maximum of 50 MPa, the strain rate was 0.1 / s, the reduction ratio was 75%, and the cooling rate after hot plastic deformation was 300°C / min.

[0116] As a modifier, Nd 0.7 Cu 0.3 Using an alloy having the composition (molar ratio), the modifying agent was diffused into the sintered body at 700°C for 165 minutes to obtain samples for Examples 1-2 and Comparative Examples 2-7. The cooling rate after diffusion was 1°C / min up to 500°C.

[0117] <Comparative Example 1> Strip cast material (magnetic tape) with the composition shown in Table 1-1 was prepared. A strip casting apparatus 70 shown in Figure 3 was used for preparation. The peripheral speed of the cooling roll 74 was 1 m / sec, and the cooling rate of the molten metal was 1000°C / sec. This strip cast material was crushed to obtain magnetic powder. This magnetic powder was compressed and molded in a magnetic field of 1 T at a pressure of 400 MPa to obtain a compact. This compact was then sintered without pressure. The temperature during pressureless sintering was 1070°C, and the pressureless sintering time was 1 hour. The sample for Comparative Example 1 was obtained by not diffusing and penetrating the modifying material into the sintered body obtained in this way.

[0118] <Comparative Example 2> The sample for Comparative Example 1 was prepared in the same manner as in Example 1, except that the composition of the liquid quenching material (magnetic thin strip) was as shown in Table 1, and the modifying material was not diffused into the sintered body.

[0119] "evaluation" The magnetic properties of each sample were measured using a PPMS (registered trademark) physical property measurement system manufactured by Quantum Design Co., Ltd. PPMS (registered trademark) is an abbreviation for Physical Property Measurement System. For the measurement, each sample was processed into a 2 mm square. The measurements were then performed at 27°C and 180°C. Unless otherwise specified, the decrease in coercivity with increasing temperature was evaluated using the temperature coefficient α. The method for calculating α is as described above.

[0120] The results are shown in Tables 1-1 and 1-2. In Table 1-2, "1-2 phase" refers to "a phase having an RFe2 type crystal structure." Furthermore, the relationship between temperature and coercivity for the samples in Examples 1-2, Comparative Example 4, and Comparative Example 7 is shown in Figure 4.

[0121] [Table 1-1]

[0122] [Table 1-2]

[0123] From Tables 1-1 to 1-2 and Figure 4, it was confirmed that in the samples of Examples 1 and 2, at least Ce and La were selected, and a portion of Fe was substituted with a predetermined proportion of Co, resulting in a small decrease in coercivity with increasing temperature and excellent desorption magnetism at room temperature. On the other hand, in the samples of Comparative Examples 1 to 7, Ce and La were not selected, or a portion of Fe was not substituted with a predetermined proportion of Co, resulting in a large decrease in coercivity with increasing temperature, an increase in coercivity at room temperature, and poor desorption magnetism at room temperature.

[0124] Based on these results, the effectiveness of the rare earth magnets disclosed herein was confirmed. [Explanation of symbols]

[0125] 10 Main phase 20 Grain boundary phase 50 Liquid quenching device 51 Spray nozzle 52 Heater 53 Cooling Roll 54 Magnetic Thin Band 55 Magnetic flakes 70 Strip Casting Machine 71 Melting furnace 72 Molten metal 73 Tan Dish 74 Cooling Rolls 75 Magnetic Alloy 100 Rare Earth Magnets Disclosed

Claims

[Claim 1] R ２ Fe １４ It comprises a main phase having a type B crystal structure (where R is a rare earth element) and a grain boundary phase surrounding the main phase. As R, at least Ce and La have been selected. The molar ratio of Ce in R is 0.20 or more and 0.45 or less, the molar ratio of La in R is 0.45 or more and 0.75 or less, and the total molar ratio of Ce and La in R is 0.65 or more and 1 or less. Some of the Fe is replaced with Co. The molar ratio of Co to the total of Fe and Co is 0.20 to 0.25, and The average particle size of the main phase is 0.05 μm or more and less than 1 μm. Rare earth magnets.

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