WO2015020182A1 - R-t-b系焼結磁石、および、モータ - Google Patents
R-t-b系焼結磁石、および、モータ Download PDFInfo
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- WO2015020182A1 WO2015020182A1 PCT/JP2014/070970 JP2014070970W WO2015020182A1 WO 2015020182 A1 WO2015020182 A1 WO 2015020182A1 JP 2014070970 W JP2014070970 W JP 2014070970W WO 2015020182 A1 WO2015020182 A1 WO 2015020182A1
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- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/0551—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 in the form of particles, e.g. rapid quenched powders or ribbon flakes
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- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
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- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
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- C—CHEMISTRY; METALLURGY
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- C22C2202/00—Physical properties
- C22C2202/02—Magnetic
Definitions
- the present invention relates to an RTB-based sintered magnet, and more particularly to an RTB-based sintered magnet in which the microstructure of the RTB-based sintered magnet is controlled, and a motor.
- RTB-based sintered magnet represented by Nd—Fe—B sintered magnet (R is a rare earth element, T is one or more iron group elements having Fe as an essential element, and B is boron) Since it has a high saturation magnetic flux density, it is advantageous for miniaturization and high efficiency of equipment used, and is used for a voice coil motor of a hard disk drive. In recent years, it is being applied to various industrial motors and drive motors for hybrid vehicles, and further spread in these fields is desired from the viewpoint of energy conservation and the like. By the way, in the application of an RTB-based sintered magnet to a hybrid vehicle or the like, since the magnet is exposed to a relatively high temperature, it is important to suppress high temperature demagnetization due to heat. It is well known that a technique of sufficiently increasing the coercive force (Hcj) at room temperature of an RTB-based sintered magnet is effective for suppressing this high temperature demagnetization.
- Hcj coercive force
- a technique for increasing the coercive force of a Nd—Fe—B sintered magnet at room temperature a technique is known in which a part of Nd of the Nd 2 Fe 14 B compound as a main phase is replaced with a heavy rare earth element such as Dy or Tb.
- a heavy rare earth element such as Dy or Tb.
- the magnetocrystalline anisotropy is increased, and as a result, the coercive force of the Nd—Fe—B sintered magnet at room temperature can be sufficiently increased.
- addition of Cu element or the like is said to be effective in improving coercivity at room temperature (Patent Document 1).
- the Cu element forms, for example, an Nd—Cu liquid phase at the grain boundary during the manufacturing process, thereby smoothing the grain boundary and suppressing the occurrence of reverse magnetic domains. .
- Patent Documents 2 and 3 disclose techniques for improving the coercive force by controlling the grain boundary phase, which is the microstructure of the RTB-based sintered magnet. From the drawings in these patent documents, it is understood that the grain boundary phase referred to here is a grain boundary surrounded by three or more main phase crystal grains, that is, a grain boundary phase existing at a triple boundary of grain boundaries.
- Patent Document 2 discloses a technique for forming two types of grain boundary phases having different Dy concentrations. That is, it is disclosed that a high resistance to magnetic domain inversion can be provided by forming a grain boundary phase having a high partial Dy concentration at the grain boundary triple point without increasing the overall Dy concentration. ing.
- Patent Document 3 three types of grain boundary phases having different total atomic concentrations of the first, second, and third rare earth elements are formed at the grain boundary triple points, and the atomic concentration of the rare earth elements in the third grain boundary phase is disclosed. Is disclosed in which the concentration of Fe element in the third grain boundary phase is made higher than the concentration in the other two types of grain boundary phases. . By carrying out like this, the 3rd grain boundary phase which contains Fe in high concentration in a grain boundary is formed, and it is supposed that this brings about the effect which improves a coercive force.
- JP 2002-327255 A JP2012-15168A JP2012-15169A
- the coercive force at room temperature is one of the effective indicators, but it is actually exposed to a high temperature environment.
- the composition in which a part of R in the R2T14B compound as the main phase is substituted with a heavy rare earth element such as Tb or Dy greatly improves the coercive force, and is a simple technique for increasing the coercive force, but the composition such as Dy and Tb is heavy. Since rare earth elements are limited in production area and production, they have resource problems.
- the grain boundary has a so-called two-grain grain boundary formed between two adjacent main phase crystal grains and a so-called grain boundary triple point surrounded by three or more main phase crystal grains. .
- the two-grain grain boundary portion formed between the two conventional R2T14B main phase crystal grains is as thin as 2 to 3 nm, and does not produce a sufficient magnetic coupling breaking effect. If the two-grain grain boundary is made extremely thick, it is considered that a sufficient magnetic coupling breaking effect can be obtained.
- the coercive force improves as the R ratio increases, if the R ratio is increased too much, the main phase crystal grains grow during sintering and the coercive force decreases. Therefore, the effect is limited only by increasing the R amount.
- the present invention has been made in view of the above, and it has been improved by suppressing the high-temperature demagnetization rate by controlling the two-particle grain boundary part, which is the microstructure of the RTB-based sintered magnet.
- An object is to provide a B-based sintered magnet and a motor including the same.
- the inventors of the present application have intensively studied a two-particle grain boundary part that can markedly improve the suppression of the high temperature demagnetization rate, and as a result, have completed the following invention.
- the RTB-based sintered magnet according to the present invention has R2T14B crystal grains and a two-grain boundary between the R2T14B crystal grains, and has an R—Co—Cu—M—Fe phase (M: Ga, Si). , Sn, Ge, Bi) is formed, and there is a two-grain grain boundary portion formed. .
- the RTB-based sintered magnet includes a two-particle grain boundary formed by an R—Co—Cu—M—Fe phase and an R—Cu—M—Fe phase (M: Ga, Si, Sn, At least one selected from Ge and Bi), and the number of two-grain grain boundaries formed by the R—Co—Cu—M—Fe phase is A, R—Cu— When the number of two-particle grain boundaries formed by the M—Fe phase is represented by B, it is preferable that A> B.
- the thickness of the two-grain grain boundary formed by the R—Co—Cu—M—Fe phase (M: at least one selected from Ga, Si, Sn, Ge, Bi) is 5 to 500 nm. preferable.
- the width of the two-grain grain boundary formed between the R2T14B crystal grains is made wider than that conventionally observed, and the two-grain grain boundary is formed. It is characterized in that the effect of breaking the magnetic coupling between the R2T14B crystal grains is remarkably enhanced by being made of a nonmagnetic or extremely weak material.
- the two-grain grain boundary part is a part formed by a grain boundary phase between two adjacent R2T14B crystal grains.
- the -M-Fe phase can form a thick two-grain boundary between 5 and 500 nm. Further, although the R—Co—Cu—M—Fe phase contains Fe and Co, the total amount of Fe and Co is extremely low at 40 atomic% or less, and it is considered that the magnetization is extremely small. Therefore, since the magnetic coupling between the R2T14B crystal grains is effectively divided, the coercive force is improved and high temperature demagnetization is suppressed.
- the R—Cu—M—Fe phase is substantially free of Co, contains 65 to 90 atomic% of Fe, and contains about 1% of Cu in terms of composition. Unlike the —Cu—M—Fe phase, it has the property of forming a thin two-grain grain boundary of the order of several nm. When the number of two-grain grain boundaries formed by the R—Co—Cu—M—Fe phase increases, the coercive force tends to improve and high temperature demagnetization tends to be suppressed. However, even if it exists in excess, it will not improve any more, but it will lead to a decrease in residual magnetic flux density Br due to a decrease in the main phase ratio.
- the present invention further provides a motor provided with the RTB-based sintered magnet of the present invention. Since the motor of the present invention includes the above-described RTB-based sintered magnet of the present invention, the RTB-based sintered magnet undergoes high temperature demagnetization even when used under severe conditions at high temperatures. Therefore, it is possible to obtain a highly reliable motor in which the output is not easily lowered.
- an RTB-based sintered magnet having a low high temperature demagnetization rate can be provided, and an RTB-based sintered magnet applicable to a motor or the like used in a high-temperature environment can be provided.
- FIG. 3 is a cross-sectional view schematically showing main phase crystal grains and two-grain grain boundaries of an RTB-based sintered magnet according to the present invention. It is a schematic diagram explaining the measuring method of the composition analysis point and width
- FIG. 3 is a cross-sectional view schematically showing the configuration of an embodiment of the motor.
- the RTB-based sintered magnet referred to in the present invention is a sintered magnet including R2T14B main phase crystal particles and a two-particle grain boundary, where R includes one or more rare earth elements, and T is It includes one or more iron group elements containing Fe as an essential element, includes B, and further includes elements to which various known additive elements are added.
- FIG. 1 is a diagram schematically showing a cross-sectional structure of an RTB-based sintered magnet according to an embodiment of the present invention.
- the RTB-based sintered magnet according to the present embodiment includes at least the R2T14B main phase crystal particles 1 and the two-grain grain boundary portion 2 formed between the adjacent R2T14B main phase crystal particles 1.
- the RTB-based sintered magnet of this embodiment is a two-particle formed by an R—Co—Cu—M—Fe phase (M: at least one selected from Ga, Si, Sn, Ge, Bi). It is characterized by the presence of grain boundaries.
- the RTB-based sintered magnet includes a two-particle grain boundary formed by an R—Co—Cu—M—Fe phase and an R—Cu—M—Fe phase (M: Ga, Si, Sn, At least one selected from Ge and Bi), and the number of two-grain grain boundaries formed by the R—Co—Cu—M—Fe phase is A, R—Cu— When the number of two-particle grain boundaries formed by the M—Fe phase is represented by B, it is preferable that A> B. Further, the thickness of the two-grain grain boundary formed by the R—Co—Cu—M—Fe phase (M: at least one selected from Ga, Si, Sn, Ge, Bi) is 5 to 500 nm. preferable.
- FIG. 2 is a schematic diagram specifically showing a method for measuring the width and composition of the two-particle grain boundary in the present embodiment.
- a two-grain grain boundary part 2 and a grain boundary triple point 3 are formed between the adjacent R2T14B main phase crystal grains 1, a two-grain grain boundary part 2 and a grain boundary triple point 3 are formed. Focusing on the two-grain grain boundary part 2 to be measured, the boundaries 2a and 2b between the two-grain grain boundary part and the grain boundary triple point 3 connected thereto are determined. The boundaries 2a and 2b do not need to be so accurate since the vicinity thereof is not measured. Divide this into four equal parts and draw three equal lines. The positions of these three bisectors are taken as the measurement points of the two-particle grain boundary width, and three measurement values are obtained. This measurement is performed on 20 arbitrarily selected two-grain grain boundaries, and the thickness (width) of a total of 60 measurement points is measured.
- composition analysis is performed at the midpoint 2c in the width direction of the two-grain grain boundary part on a line that bisects the boundaries 2a and 2b.
- phase is classified and tabulated.
- the classification of the composition of the grain boundary phase present in the two-grain grain boundary is performed according to the compositional characteristics of each phase described below.
- the compositional characteristics of the R—Co—Cu—M—Fe phase are as follows: the total R is 40 to 70 atomic%, Co is 1 to 10 atomic%, Cu is 5 to 50 atomic%, and M is 1 to 15 atoms. %, And Fe is contained in an amount of 1 to 40 atomic%.
- compositional characteristics of the R—Cu—M—Fe phase include a total of 10 to 20 atomic% of R, Co of less than 0.5 atomic%, Cu of less than 1 atomic%, and M of 1 to 10 atomic%. Fe is contained in an amount of 65 to 90 atomic%.
- the R6T13M phase and the R phase are included in addition to the R—Co—Cu—M—Fe phase and the R—Cu—M—Fe phase.
- the R6T13M phase is characterized in that the total of R is 26 to 30 atomic%, Co is less than 2 atomic%, M is 1 to 10 atomic%, and the balance is Fe and other elements 60 to 70 atomic%.
- the characteristic of the R phase is that the total of R is 90 atomic% or more.
- elements intentionally added to the RTB-based sintered magnet or inevitable impurities may be classified according to the above characteristics even if a small amount, for example, less than several percent, is detected. Anything that does not fall under any of these may be treated as other phases.
- the rare earth element R may be any of a light rare earth element, a heavy rare earth element, or a combination of both. From the viewpoint of material cost, Nd, Pr, or a combination of both is preferable.
- the iron group element T is preferably Fe or a combination of Fe and Co, but is not limited thereto.
- B represents boron.
- the content of each element with respect to the total mass is as follows. In this specification, mass% is regarded as the same unit as weight%.
- R 25 to 35% by mass
- B 0.5 to 1.5% by mass
- M 0.01 to 1.5% by mass
- Cu 0.01 to 1.5% by mass
- Co 0.3 to 3.0% by mass
- Al 0.03 to 0.6% by mass
- Fe substantially the balance
- the total content of elements other than Fe among the elements occupying the balance More preferably 5% by mass or less, R: 29.5-33.1% by mass, B: 0.75 to 0.95% by mass, M: 0.01 to 1.0% by mass, Cu: 0.01 to 1.5% by mass, Co: 0.3 to 3.0% by mass, Al: 0.03 to 0.6% by mass, Fe: substantially the balance, and
- the total content of elements other than Fe among the elements occupying the balance is 5% by mass or less, and within this composition range, the R—Co—Cu—M—Fe phase is easily formed.
- the R content of the RTB-based sintered magnet according to this embodiment is 25 to 35% by mass.
- the heavy rare earth element refers to a rare earth element having a large atomic number, and generally corresponds to a rare earth element from 64 Gd to 71 Lu.
- the content of R is within this range, high residual magnetic flux density and coercive force tend to be obtained. If the R content is less than this, the R2T14B phase, which is the main phase, becomes difficult to form, and an ⁇ -Fe phase having soft magnetism is likely to be formed, resulting in a decrease in coercive force.
- the content of R is larger than this, the volume ratio of the R2T14B phase is lowered, and the residual magnetic flux density is lowered.
- the sintering temperature start temperature is extremely lowered and grain growth is facilitated.
- a more preferable range of the R content is 29.5 to 33.1% by mass.
- R necessarily contains either Nd or Pr, but the ratio of Nd and Pr in R is 80 to 100 atomic% in total of Nd and Pr, and more preferably 95 to 100 atomic%. . Within such a range, better residual magnetic flux density and coercive force can be obtained.
- the RTB-based sintered magnet may contain heavy rare earth elements such as Dy, Tb, and Ho as R. In this case, the entire RTB-based sintered magnet The content of heavy rare earth elements in the mass is 1.0% by mass or less in total of the heavy rare earth elements, preferably 0.5% by mass or less, and more preferably 0.1% by mass or less. According to the RTB-based sintered magnet of the present embodiment, even if the content of heavy rare earth elements is reduced in this way, the content and atomic ratio of other elements satisfy a specific condition, Good high coercive force can be obtained.
- the RTB-based sintered magnet according to this embodiment includes B.
- the content of B is 0.5% by mass or more and 1.5% by mass or less, preferably 0.7% by mass or more and 1.2% by mass or less, more preferably 0.75% by mass or more and 0.95% by mass. It is as follows. When the content of B is less than 0.5% by mass, the coercive force HcJ tends to decrease. On the other hand, if the B content exceeds 1.5% by mass, the residual magnetic flux density Br tends to decrease. In particular, when the B content is in the range of 0.75 mass% to 0.95 mass%, the R—Co—Cu—M—Fe phase is easily formed.
- the RTB-based sintered magnet according to this embodiment includes Co.
- the Co content is preferably 0.3% by mass or more and 3.0% by mass or less.
- the added Co is present in any of the main phase crystal grains, the grain boundary triple points, and the two-grain grain boundary part, and the Curie temperature is improved and the corrosion resistance of the grain boundary phase is improved. Furthermore, high temperature demagnetization can be suppressed by forming a two-grain grain boundary portion in the R—Co—Cu—M—Fe phase. Co may be added at the time of producing the alloy, or may be contained together with Cu, M, or the like by diffusion at the grain boundaries described later or by being diffused alone in the sintered body.
- the RTB-based sintered magnet according to this embodiment includes Cu.
- the amount of Cu added is preferably 0.01 to 1.5% by mass, more preferably 0.05 to 1.5% by mass. By setting the addition amount within this range, Cu can be unevenly distributed almost only at the grain boundary triple point and the two grain boundary part. High-temperature demagnetization can be suppressed by Cu unevenly distributed in the grain boundary triple point and the two-grain grain boundary part forming the R—Co—Cu—M—Fe phase.
- Cu may be added at the time of alloy preparation, or may be contained together with Co, M, etc. by grain boundary diffusion described later or by being diffused alone in the sintered body.
- the RTB-based sintered magnet according to this embodiment further includes M.
- M represents at least one selected from Ga, Si, Sn, Ge, and Bi.
- a preferable content of M is 0.01 to 1.5% by mass. If the M content is less than this range, the suppression of high temperature demagnetization is insufficient, and if it is more than this range, the high temperature demagnetization will not be further improved, and the saturation magnetization will be lowered, resulting in an insufficient residual magnetic flux density. It will be enough.
- the M content is more preferably 0.1 to 1.0% by mass.
- M may be added at the time of producing the alloy, or may be contained by being diffused into the sintered body together with Co, Cu or the like alone by grain boundary diffusion described later. Among M, Ga is particularly preferable.
- the RTB based sintered magnet of this embodiment preferably contains Al.
- Al By containing Al, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained magnet.
- the Al content is preferably 0.03% by mass or more and 0.6% by mass or less, and more preferably 0.05% by mass or more and 0.25% by mass or less.
- the RTB-based sintered magnet according to this embodiment includes Fe and other elements in addition to the above-described elements, and Fe and other elements are included in the total mass of the RTB-based sintered magnet. The remainder accounts for the content excluding the total content of the above elements. However, in order for the RTB-based sintered magnet to sufficiently function as a magnet, the total content of elements other than Fe among the elements occupying the balance is the total content of the RTB-based sintered magnet. It is preferable that it is 5 mass% or less with respect to mass.
- the content of C in the RTB-based sintered magnet according to the present embodiment is 0.05 to 0.3% by mass.
- the C content is less than this range, the residual magnetic flux density is insufficient.
- the C content is more than this range, the ratio of the magnetic field value (Hk) to the coercive force when the magnetization is 90% of the residual magnetic flux density.
- the so-called squareness ratio (Hk / coercive force) becomes insufficient.
- the C content is preferably 0.1 to 0.25% by mass.
- the content of O in the RTB-based sintered magnet according to this embodiment is preferably 0.05 to 0.25% by mass. If the O content is less than this range, the corrosion resistance of the RTB-based sintered magnet will be insufficient, and if it exceeds this range, the liquid phase will be sufficient in the RTB-based sintered magnet. And the coercive force decreases. In order to obtain better corrosion resistance and coercive force, the O content is more preferably 0.05 to 0.20% by mass.
- the RTB-based sintered magnet according to the present embodiment can contain, for example, Zr as another element.
- the Zr content is preferably 0.01 to 1.5% by mass or less based on the total mass of the RTB-based sintered magnet.
- Zr can suppress abnormal growth of crystal grains in the manufacturing process of the RTB-based sintered magnet, and the structure of the obtained sintered body (RTB-based sintered magnet) is uniform and It is possible to improve the magnetic characteristics by reducing the size.
- the RTB-based sintered magnet according to the present embodiment contains 0.001 to 0.5 mass of inevitable impurities such as Mn, Ca, Ni, Cl, S, and F as constituent elements other than those described above. % May be included.
- the N content of the RTB-based sintered magnet according to this embodiment is preferably 0.15% by mass or less. If the N content is more than this range, the coercive force tends to be insufficient.
- the RTB-based sintered magnet according to the present embodiment can be manufactured by an ordinary powder metallurgy method.
- This powder metallurgy method includes a preparation step for preparing a raw material alloy, a raw material alloy by pulverizing the raw material alloy There are a pulverizing step, a forming step of forming a raw material powder to form a molded body, a sintering step of sintering the molded body to obtain a sintered body, and a heat treatment step of subjecting the sintered body to an aging treatment.
- the preparation step is a step of preparing a raw material alloy having each element included in the RTB-based sintered magnet according to the present embodiment.
- a raw metal having a predetermined element is prepared, and a strip casting method or the like is performed using these.
- a raw material alloy can be prepared.
- the raw metal include rare earth metals, rare earth alloys, pure iron, pure cobalt, pure copper, ferroboron, and alloys thereof.
- a raw material alloy is prepared so that an RTB-based sintered magnet having a desired composition can be obtained.
- the 1st alloy with a composition close to R2T14B, and the 2nd alloy which mainly increased the amount of R or an additive and you may mix before or after the below-mentioned pulverization process.
- R having a different composition from the second alloy and an alloy having an increased amount of additive are referred to as a third alloy
- an alloy having an additional R and the composition having a different composition from those of the second and third alloys are referred to as a fourth alloy.
- the pulverization step is a step of pulverizing the raw material alloy obtained in the preparation step to obtain a raw material fine powder. This process is preferably performed in two stages, a coarse pulverization process and a fine pulverization process, but may be performed in one stage.
- the coarse pulverization step can be performed in an inert gas atmosphere using, for example, a stamp mill, a jaw crusher, a brown mill, or the like. It is also possible to perform hydrogen occlusion and pulverization in which hydrogen is occluded and then pulverized.
- the raw material alloy is pulverized until the particle size becomes several hundred ⁇ m to several mm.
- the coarse powder obtained in the coarse pulverization step is finely pulverized to prepare a raw material fine powder having an average particle size of about several ⁇ m.
- the average particle size of the raw material fine powder may be set in consideration of the degree of crystal grain growth after sintering.
- the fine pulverization can be performed using, for example, a jet mill.
- the forming step is a step of forming a compact by forming the raw material fine powder in a magnetic field. Specifically, after forming the raw material fine powder into a mold arranged in an electromagnet, molding is performed by applying a magnetic field with an electromagnet and pressing the raw material fine powder while orienting the crystal axis of the raw material fine powder. I do.
- the molding in the magnetic field may be performed at a pressure of about 30 to 300 MPa in a magnetic field of 1000 to 1600 kA / m, for example.
- the sintering step is a step of obtaining a sintered body by sintering the formed body. After molding in a magnetic field, the compact can be sintered in a vacuum or an inert gas atmosphere to obtain a sintered compact.
- the sintering conditions are preferably set as appropriate according to conditions such as the composition of the molded body, the method of pulverizing the raw material fine powder, and the particle size, but may be performed at 1000 ° C. to 1100 ° C. for about 1 to 12 hours, for example. Also, eutectic alloys such as 80% Nd-20% Co, 70% Nd-30% Cu, 80% Nd-20% Ga, etc. are used as the second alloy, the third alloy, and the fourth alloy in the adjusting step.
- the temperature in the temperature range of 500 to 900 ° C., where the melting point of each eutectic alloy is, is increased in the temperature rising process in the sintering process so that the liquid phases generated from each eutectic alloy easily react. Slowly promotes the formation of the R—Co—Cu—M—Fe phase.
- the temperature elevation rate may be controlled taking into consideration the composition and the fine structure.
- the heat treatment step is a step of aging the sintered body. After this step, the width of the two-grain grain boundary portion formed between adjacent R2T14B main phase crystal grains and the composition of the grain boundary phase formed at the two-grain grain boundary portion are determined. However, these microstructures are not controlled only by this process, but are determined by a balance between the above-described various conditions of the sintering process and the state of the raw material fine powder. Therefore, the heat treatment temperature and time may be set in consideration of the relationship between the heat treatment conditions and the microstructure of the sintered body.
- the heat treatment may be performed in a temperature range of 500 ° C. to 900 ° C. However, the heat treatment may be performed in two stages, such as a heat treatment near 800 ° C.
- the width of the two-grain boundary can be controlled.
- an example of the heat treatment process has been described as a method for controlling the width of the two-grain grain boundary part.
- the width of the two-grain grain boundary part can also be controlled by a composition factor as described in Table 1. .
- each element of R, Co, Cu, M, and Fe forming the R—Co—Cu—M—Fe phase is introduced into the sintered body after producing the sintered body by the grain boundary diffusion method. Also good.
- Co, Cu, and M can be distributed at a high concentration in the grain boundary including the grain boundary triple point and the two-grain grain boundary, and the R—Co—Cu—M—Fe phase It is considered advantageous for formation.
- Co dissolves in the R2T14B main phase particles
- a grain boundary diffusion method in which elements are diffused into the sintered body using the grain boundaries as a path, solid solution in the main phase is suppressed, and Co in the grain boundaries is reduced.
- the concentration of Cu and Ga can be increased.
- the grain boundary diffusion method there is known a method of heat-treating a diffusion element as a vapor or attaching a solid diffusion material powder to the surface of a sintered body, and any method may be used.
- the diffusion heat treatment is preferably performed at 550 ° C. to 1000 ° C. for about 1 to 24 hours. In this temperature range, the grain boundary triple point and the grain boundary phase of the two grain boundary part become a liquid phase and ooze out to the surface of the sintered body.
- the diffusing element is supplied into the sintered body through the exuded liquid phase.
- Co, Cu, and M may be diffused at grain boundaries.
- Co, Cu, and M all have a eutectic composition on the R-rich side, and all have a relatively low melting point.
- the melted diffusing material can efficiently supply the diffusing element to the liquid phase exuded from the sintered body.
- an eutectic alloy of R—Co, R—Cu, and RM has a low melting point, and these may be used as a diffusion material. In that case, diffusion may be performed using a mixed powder of R—Co, R—Cu, and RM.
- the grain boundary diffusion heat treatment all necessary elements may be diffused at one time, but it is preferable that the grain boundary diffusion heat treatment is divided into a plurality of times depending on the element and diffused by separate heat treatments.
- the heat treatment during and after the introduction is particularly important for the formation of the two-grain grain boundary, but as in the previous paragraph, the heat treatment temperature and the heat treatment temperature and the microstructure of the sintered body are taken into consideration, as in the previous paragraph. Set the time.
- the RTB system sintered magnet according to this embodiment can be obtained by the above method, but the manufacturing method of the RTB system sintered magnet is not limited to the above, and may be changed as appropriate.
- the sample shape for evaluation is not particularly limited, in this embodiment, an RTB-based sintered magnet having a rectangular parallelepiped shape of 10 mm ⁇ 10 mm ⁇ 4 mm is used as an example.
- the c-axis orientation direction of the R2T14B crystal grains is a direction perpendicular to a wide surface of 10 mm ⁇ 10 mm.
- the high temperature demagnetization factor D (B1-B0) / B0 ⁇ 100 (%) It is evaluated.
- observation using a scanning transmission electron microscope is performed to identify the position of the midpoint 2c of the two-grain boundary in FIG. 2, and the thickness of the two-grain boundary is measured. Furthermore, the content ratio of each element at the midpoint 2c of the two-grain boundary is calculated by point analysis using an energy dispersive X-ray spectrometer (STEM-EDS) attached to the STEM, The composition of the existing grain boundary phase.
- STEM scanning transmission electron microscope
- the RTB-based sintered magnet according to the present embodiment obtained in this manner is less likely to cause a decrease in output because high-temperature demagnetization is unlikely to occur when used in a magnet for a rotating machine such as a motor.
- a rotating machine such as a high motor can be manufactured.
- the RTB-based sintered magnet according to the present embodiment includes an embedded internal magnet such as a surface permanent magnet (SPM) motor having a magnet attached to the rotor surface and an inner rotor type brushless motor. It is suitably used as a magnet of a type (Interior Permanent Magnet: IPM) motor, PRM (Permanent Magnet Reluctance Motor), or the like.
- SPM surface permanent magnet
- IPM Interior Permanent Magnet
- PRM Permanent Magnet Reluctance Motor
- the RTB-based sintered magnet according to the present embodiment includes a spindle motor and a voice coil motor for driving a hard disk in a hard disk drive, a motor for an electric vehicle and a hybrid car, and a motor for an electric power steering of the automobile. It is suitably used as a servomotor for machine tools, a vibrator motor for mobile phones, a printer motor, a generator motor, and the like.
- FIG. 3 is a cross-sectional view schematically showing a configuration of an embodiment of the SPM motor.
- the SPM motor 10 includes a columnar rotor 12 and a cylindrical stator 13 in a housing 11. And a rotating shaft 14. The rotating shaft 14 passes through the center of the cross section of the rotor 12.
- the rotor 12 includes a columnar rotor core (iron core) 15 made of an iron material, a plurality of permanent magnets 16 provided on the outer peripheral surface of the rotor core 15 at a predetermined interval, and a plurality of magnet insertion slots for housing the permanent magnets 16. 17.
- the permanent magnet 16 the RTB-based sintered magnet according to this embodiment is used.
- a plurality of permanent magnets 16 are provided in the magnet insertion slots 17 along the circumferential direction of the rotor 12 so that N poles and S poles are alternately arranged. Thereby, the permanent magnets 16 adjacent along the circumferential direction generate magnetic lines of force in opposite directions along the radial direction of the rotor 12.
- the stator 13 has a plurality of stator cores 18 and throttles 19 provided at predetermined intervals along the outer peripheral surface of the rotor 12 in the circumferential direction inside the cylindrical wall (peripheral wall).
- the plurality of stator cores 18 are provided to face the rotor 12 toward the center of the stator 13.
- a coil 20 is wound around each throttle 19.
- the permanent magnet 16 and the stator core 18 are provided so as to face each other.
- the rotor 12 is provided so as to be rotatable in a space in the stator 13 together with the rotating shaft 14.
- the stator 13 applies torque to the rotor 12 by electromagnetic action, and the rotor 12 rotates in the circumferential direction.
- the SPM motor 10 uses the RTB system sintered magnet according to the present embodiment as the permanent magnet 16. Since the permanent magnet 16 has high magnetic characteristics and is difficult to demagnetize at high temperatures, the SPM motor 10 can improve motor performance such as motor torque characteristics, maintain high output, Excellent in properties.
- the sintered bodies used in Examples 1 to 7 and Comparative Examples 1 and 2 were produced by the two alloy method.
- a raw material alloy was prepared by a strip casting method so that RTB-based sintered magnets having magnet compositions I and II shown in Tables 1 and 2 were obtained.
- As the raw material alloys four types of first alloys A and B that mainly form the main phase of the magnet and second alloys a and b that mainly form the grain boundary phase were prepared and prepared.
- bal. Indicates the remainder when the total composition of each alloy is 100% by mass
- (T.RE) indicates the total mass% of the rare earth.
- each process (fine pulverization and molding) from the hydrogen pulverization treatment to sintering was performed in an Ar atmosphere having an oxygen concentration of less than 50 ppm (the same applies to the following examples and comparative examples).
- the raw material powder of the first alloy and the raw material powder of the second alloy are mixed at a mass ratio of 95: 5, and the mixed powder that is the raw material powder of the RTB-based sintered magnet is obtained. Prepared.
- the obtained mixed powder was filled in a mold placed in an electromagnet, and molded in a magnetic field in which a pressure of 120 MPa was applied while applying a magnetic field of 1200 kA / m to obtain a molded body.
- the obtained molded body was heated at 10 ° C./min in vacuum, held at 1060 ° C. for 4 hours and sintered, and then rapidly cooled to obtain the magnet composition I and magnet composition II shown in Table 1.
- a sintered body (RTB-based sintered magnet) was obtained. Then, it grind-processed with the vertical processing machine, and was set as the rectangular parallelepiped of 10.1 mm x 10.1 mm x 4.2 mm. The orientation direction of the c-axis of the R2T14B crystal grains was set to be 4.2 mm thick.
- a diffusion material for introducing Co, Cu, and M elements into the sintered body was produced by a grain boundary diffusion method using a diffusion material powder.
- a single metal was weighed so as to have a diffusing material composition of 1 to 8 shown in Table 3, and melting and casting were repeated three times in an arc melting furnace to produce an alloy.
- the obtained alloy was melted by high frequency induction heating, and the molten metal was quenched and rolled to form a quenched ribbon.
- the obtained quenched ribbon was coarsely pulverized in an Ar-substituted glove box and placed in an Ar-substituted airtight container together with a stainless steel pulverizing medium.
- the coarsely pulverized powder was pulverized in an airtight container to obtain a powder having an average particle size of 10 to 20 ⁇ m.
- the obtained diffusing material powder was collected in a glove box and subjected to a gradual oxidation treatment so that it could be handled safely in the air.
- a binder resin was added to the diffusing material powder thus obtained, and a coating material for the diffusing material was prepared using alcohol as a solvent.
- alcohol As for the mixing ratio, when the mass of the diffusing material powder is 100, butyral fine powder as a binder resin is 2, and alcohol is 100.
- the mixture was put in a resin-made cylindrical lidded container in an Ar atmosphere, the lid was closed, and the mixture was placed on a ball mill frame and rotated at 120 rpm for 24 hours to form a paint.
- Comparative Example 1 A sintered compact processed product of magnet composition II was subjected to an aging treatment at 900 ° C. for 18 hours and then at 540 ° C. for 2 hours (both in an Ar atmosphere). This was designated as Comparative Example 1.
- the diffusing material 8 shown in Table 3 was applied to a sintered compact processed product (10.1 mm ⁇ 10.1 mm ⁇ 4.2 mm) having a magnet composition I.
- the coating was uniformly applied to two wide surfaces of 10.1 mm ⁇ 10.1 mm, and the total of the two surfaces was 5.5 wt%.
- a diffusion heat treatment at 900 ° C. for 6 h was performed in an Ar atmosphere, and the diffusion material residue on the coated surface was removed with sandpaper.
- the same amount of the diffusing material 8 was applied again, and diffusion heat treatment was performed at 900 ° C. for 6 hours in the same Ar atmosphere, and the diffusing material residue on the coated surface was similarly removed.
- diffusion heat treatment was performed at 900 ° C. for 6 hours. That is, the application of 5.5 wt% diffusion material 8 and the heat treatment at 900 ° C. for 6 hours in Ar were repeated three times.
- an aging treatment was performed at 540 ° C. for 2 hours in an Ar atmosphere. The residue of the diffusing material on the surface coated with the diffusing material was removed with sandpaper to obtain an RTB-based sintered magnet.
- Examples 1 to 5 The sintered body processed product of the magnet composition I (10.1 mm ⁇ 10.1 mm ⁇ 4.2 mm) and the diffusion materials 3 to 7 in Table 3 in the amount shown in Table 3 in the total amount of two surfaces are 10.1 mm ⁇ 10
- the film was evenly applied to two wide surfaces of 1 mm and subjected to diffusion heat treatment at 900 ° C. for 6 hours in an Ar atmosphere. After the heat treatment, the diffusing material residue on the diffusing material application surface was removed with sandpaper. Next, the diffusion material 2 was applied in a total of 4.5 wt% on the two surfaces, and similarly heat treated at 900 ° C. for 6 hours in an Ar atmosphere.
- the diffusing material residue on the coated surface was dropped with sandpaper, and the diffusing material 1 was applied in a total of 5.5 wt% on the two surfaces, and similarly heat treated at 900 ° C. for 6 hours in an Ar atmosphere.
- an aging treatment was performed at 540 ° C. for 2 hours in an Ar atmosphere.
- the residue of the diffusing material on the diffusing material application surface was removed with sandpaper to obtain an RTB-based sintered magnet.
- the diffusing material type was changed in the initial diffusion heat treatment, the cases where the diffusing materials 3, 4, 5, 6, and 7 were used were referred to as Examples 1, 2, 3, 4, and 5, respectively.
- Example 6 The sintered body processed product of magnet composition I (10.1 mm ⁇ 10.1 mm ⁇ 4.2 mm) and the diffusing material 3 of Table 3 are equally distributed over two surfaces of 10.1 mm ⁇ 10.1 mm in a total of 3.8 wt. %, And a diffusion heat treatment was performed at 800 ° C. for 10 hours in an Ar atmosphere. After the heat treatment, the residue on the diffusing material application surface was removed with sandpaper, then 4.5 wt% of the diffusing material 2 was applied, and similarly heat treatment was performed at 800 ° C. for 10 hours in an Ar atmosphere.
- the diffusing material residue on the coated surface was dropped with sandpaper, and the diffusing material 1 was applied by 5.5 wt%, and similarly, heat treatment was performed at 800 ° C. for 10 hours in an Ar atmosphere. Next, an aging treatment was performed at 540 ° C. for 2 hours in an Ar atmosphere. The residue of the diffusing material on the diffusing material application surface was removed with sandpaper to obtain an RTB-based sintered magnet.
- Example 7 The sintered body processed product of the magnet composition I (10.1 mm ⁇ 10.1 mm ⁇ 4.2 mm) and the diffusion material 1 of Table 3 are evenly distributed on two surfaces of 10.1 mm ⁇ 10.1 mm and 5.5 wt. %, And a diffusion heat treatment was performed at 900 ° C. for 6 hours in an Ar atmosphere. After the heat treatment, the residue on the diffusion material application surface was removed with sandpaper, and then 4.4 wt% of the diffusion material 2 was applied and similarly heat treatment was performed at 900 ° C. for 6 hours in an Ar atmosphere.
- the diffusing material residue on the coated surface was dropped with sandpaper, 5.4 wt% of the diffusing material 3 was applied, and similarly, heat treatment was performed at 900 ° C. for 10 hours in an Ar atmosphere. Next, an aging treatment was performed at 540 ° C. for 2 hours in an Ar atmosphere. The residue of the diffusing material on the diffusing material application surface was removed with sandpaper to obtain an RTB-based sintered magnet.
- the comparative examples 1, 2 and examples 1 to 7 were collectively ground and processed into a rectangular parallelepiped of 10.0 mm ⁇ 10.0 mm ⁇ 4.0 mm.
- Table 4 shows the results of the composition analysis by fluorescent X-ray and ICP. Comparative Examples 1 and 2 and Examples 1, 6, and 7 had almost the same composition. In Examples 1 to 5, the types and amounts of M (Ga, Si, Sn, Ge, Bi) contained were different, but the other compositions were the same. In the sample using the grain boundary diffusion method, an increase in Co, Cu, and M is observed, but an increase in Nd that accounts for 70% or more in the atomic ratio of the coating component is slight. This is thought to be because the Nd concentration at the grain boundaries including the grain boundary triple points and the two-grain grain boundaries contained in the sintered body is high, and the concentration gradient necessary for diffusion inside the sintered body cannot be obtained sufficiently. It is done. That is, from this, the present invention does not improve the characteristics by increasing the R amount.
- M Ga, Si, Sn, Ge, Bi
- composition analysis at point 2c on the grain boundary of each sample by TEM-EDS and the thickness of the two-grain grain boundary part were measured by the above-described method.
- Table 5 shows the result of classifying the grain boundary phase existing in the two-grain grain boundary portion by the composition analysis value as described above together with the residual magnetic flux density Br, the coercive force Hcj, and the high temperature demagnetization factor.
- the R—Co—Cu—M—Fe phase does not exist, and the number of R—Cu—M—Fe phases is large.
- Examples 1 to 5 there are R—Co—Cu—M—Fe phases, and the number of R—Co—Cu—M—Fe phases (A) and the number of R—Cu—M—Fe phases (B ) Is A> B. Regarding the number of R6Fe13M phases (C) and the number of R phases (D), there was no significant difference between the comparative example and the example. Hcj and the high temperature demagnetization rate are greatly improved in Examples 1 to 5 in which the R—Co—Cu—M—Fe phase is present, and the decrease in Br is also suppressed.
- Example 6 the same combination of diffusing materials as in Example 1 is used, but the number of R—Co—Cu—M—Fe phases (A) and R—Cu—M— are different depending on the heat treatment time.
- the number of Fe phases (B) changed.
- A was equal to or greater, but B was 0.
- Hcj and high temperature demagnetization rate are hardly changed, but Br is lowered.
- Example 7 the same combination of diffusing materials as in Example 1 was used, but the number of R—Co—Cu—M—Fe phases (A) and R—Cu— The number (B) of M-Fe phases changed.
- A> B but in Example 7, A ⁇ B.
- the Br is high but the Hcj and the high temperature demagnetization factor are inferior compared with the examples 1 to 5.
- Table 6 shows the measurement results of the thickness of the two-particle grain boundary.
- the two-grain grain boundary formed by the R—Co—Cu—M—Fe phase is obviously thick in the range of 5 to 500 nm.
- the two-grain grain boundary formed by the R—Cu—M—Fe phase is as thin as 2 to 15 nm, and it is considered that the decrease in the volume ratio of the main phase can be suppressed.
- the R6T13M phase and the R phase also form thick two-grain grain boundaries, but the number is small from Table 5. From this, it is considered that the formation of the two-grain grain boundary portion by the R—Co—Cu—M—Fe phase contributes to the improvement of the high temperature demagnetization rate.
- Table 7 shows the composition of the R—Co—Cu—M—Fe phase confirmed in Example 1.
- the Fe content is very low at 35.7 atomic% or less, and the magnetization is considered to be significantly lower than that of the conventionally known grain boundary phase. It is also characteristic that the concentration of Cu is very high.
- M is Ga, but in Examples 2 to 7 using other M elements, the composition of the R—Co—Cu—M—Fe phase is the same and can be classified by the above classification method. It was.
- Examples 8 to 11 attempted to improve the high temperature demagnetization rate by different processes.
- Raw material alloys for producing sintered bodies having the magnet compositions III to VI shown in Tables 8 to 11 were produced.
- the compositions of Examples 8, 9, 10, and 11 are magnet compositions III, IV, V, and VI, respectively.
- Each first alloy in Tables 8 to 11 was produced by a strip casting method.
- the compositions of the second, third, and fourth alloys were the same as the compositions of the diffusing materials 1, 2, and 3, and the roll quenched ribbon was pulverized to 40 ⁇ m or less following the above-described method for producing the diffusing material.
- 0.1 wt% of zinc stearate was added without performing gradual oxidation treatment, and further pulverized to an average particle size of 4 ⁇ m by a jet mill. Thereafter, using a Nauta mixer, mixed powders of the raw material fine powders of the first to fourth alloys in the proportions shown in the table were prepared. The obtained mixed powder was filled in a mold placed in an electromagnet, and molded in a magnetic field in which a pressure of 120 MPa was applied while applying a magnetic field of 1200 kA / m, to obtain a molded body. The obtained molded body was sintered in vacuum. At that time, the temperature range of 500 to 900 ° C.
- the temperature increasing portion of the sintering temperature pattern was increased at 0.5 ° C./min, and the temperature range other than that was increased to 1060 ° C. at 10 ° C./min. After being held at 1060 ° C. for 4 hours to sinter, it was quenched. Thereafter, an aging treatment was performed at 900 ° C. for 18 hours and then at 540 ° C. for 2 hours (both in an Ar atmosphere).
- the obtained RTB-based sintered magnet was ground to obtain a rectangular parallelepiped of 10.0 mm ⁇ 10.0 mm ⁇ 4.0 mm.
- the orientation direction of the c-axis of the R2T14B crystal grains was set to be 4.0 mm thick.
- Comparative Examples 3 to 6 sintered bodies having the same magnet compositions III to VI as in Examples 8 to 11 were produced.
- the raw material alloys of these comparative examples the first alloy and the second alloy produced by the strip casting method were used.
- the compositions of Comparative Examples 3, 4, 5, and 6 are magnet compositions III, IV, V, and VI, respectively, in this order.
- Tables 12 to 15 show the alloy compositions used to produce the sintered bodies of the respective magnet compositions of Comparative Examples 3 to 6.
- the manufacturing process of Comparative Examples 3 to 6 is the same as that of Comparative Example 1.
- the obtained RTB-based sintered magnet was ground to obtain a rectangular parallelepiped of 10.0 mm ⁇ 10.0 mm ⁇ 4.0 mm.
- the orientation direction of the c-axis of the R2T14B crystal grains was set to be 4.0 mm thick.
- the formation process of the R—Co—Cu—M—Fe phase is not clear, but the second alloy has a liquid phase formation temperature of 625 ° C., the third alloy has 520 ° C., and the fourth alloy has a liquid phase formation temperature of 651 ° C.
- the liquid phases of the second, third, and fourth alloys can easily react with each other, and R It is considered that the formation of the —Co—Cu—M—Fe phase is promoted.
- Table 17 shows the measurement results of the thickness of the two-particle grain boundary. As in Examples 1 to 7, it was confirmed that the two-grain grain boundary formed by the R—Co—Cu—M—Fe phase was as thick as 8 to 444 nm.
- Table 18 shows the composition of the R—Co—Cu—M—Fe phase confirmed in Examples 8 to 11 for each sample. In both cases, the Fe content was very low at 27.4 atomic% or less, and it was also confirmed that the Cu concentration was very high, which was the same as the results in Table 7 above.
- the RTB-based sintered magnet of the example has a two-particle grain boundary formed by the R—Co—Cu—M—Fe phase.
- the thickness of the two-grain grain boundary formed by the R—Co—Cu—M—Fe phase was 5 to 500 nm.
- the coercive force was improved and the high temperature demagnetization rate was improved.
- the two-grain grain boundary formed by the simultaneously present R—Cu—M—Fe phase is thin and does not reduce the volume ratio of the main phase, which is effective in suppressing the decrease in residual magnetic flux density.
- the presence of the two-grain grain boundary portion formed by the R-Cu-M-Fe phase and the balance with the amount of the two-grain grain boundary portion formed by the R-Co-Cu-M-Fe phase are excellent. Both high temperature demagnetization rate and high residual magnetic flux density can be achieved.
- an RTB-based sintered magnet that can be used even in a high-temperature environment can be provided.
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Abstract
Description
R:25~35質量%、
B:0.5~1.5質量%、
M:0.01~1.5質量%、
Cu:0.01~1.5質量%、
Co:0.3~3.0質量%、
Al:0.03~0.6質量%、
Fe:実質的に残部、及び、
残部を占める元素のうちのFe以外の元素の合計含有量:5質量%以下
より好ましくは、
R:29.5~33.1質量%、
B:0.75~0.95質量%、
M:0.01~1.0質量%、
Cu:0.01~1.5質量%、
Co:0.3~3.0質量%、
Al:0.03~0.6質量%、
Fe:実質的に残部、及び、
残部を占める元素のうちのFe以外の元素の合計含有量:5質量%以下
であり、この組成範囲であると、R-Co-Cu-M-Fe相が形成されやすい。
D=(B1-B0)/B0×100(%)
と、評価される。
次に、本実施形態に係るR-T-B系焼結磁石をモータに用いた好適な実施形態について説明する。ここでは、本実施形態に係るR-T-B系焼結磁石をSPMモータに適用した一例について説明する。図3は、SPMモータの一実施形態の構成を簡略に示す断面図であり、図3に示すように、SPMモータ10は、ハウジング11内に、円柱状のロータ12と、円筒状のステータ13と、回転軸14とを有する。回転軸14はロータ12の横断面の中心を貫通している。
実施例1~7、比較例1、2に用いる焼結体の作製を2合金法で行った。まず、表1および表2に示す磁石組成IおよびIIを有するR-T-B系焼結磁石が得られるように、ストリップキャスティング法により原料合金を準備した。原料合金としては、主に磁石の主相を形成する第1合金AおよびBと、主に粒界相を形成する第2合金aおよびbの計4種類を作製して準備した。なお、表1および表2(後述する表3も同様)では、bal.は、各合金の全体組成を100質量%とした場合の残りを示し、(T.RE)は、希土類の合計質量%を示す。
拡散材粉末を用いた粒界拡散法により焼結体内にCo、Cu、M元素を導入するための拡散材を作製した。表3に示す1~8の拡散材組成となるように単体金属を秤量してアーク溶解炉で溶解・鋳造を3回繰り返して合金を作製した。得られた合金を高周波誘導加熱で熔解し、熔湯をロール急冷することにより急冷薄帯とした。得られた急冷薄帯をAr置換されたグローブボックス中で粗粉砕し、ステンレス製の粉砕メディアとともにAr置換された密閉容器に入れた。粗粉砕粉を密閉容器内で粉砕して平均粒径10~20μmの粉末を得た。なお、得られた拡散材粉末は、グローブボックス中で回収し、大気中で安全に扱えるように徐酸化処理を施した。そのようにして得られた拡散材粉末にバインダー樹脂を添加し、アルコールを溶媒として拡散材の塗料を作製した。混合の比率は拡散材粉末の質量を100とした場合、バインダー樹脂としてのブチラール微粉末を2、アルコールを100とした。Ar雰囲気中で樹脂製の円筒形フタ付き容器に前記混合物を入れてフタを閉め、ボールミル架台に置き24時間120rpmで回転させて塗料化した。
磁石組成IIの焼結体加工品を、900℃で18時間、次いで、540℃で2時間(ともにAr雰囲気下)の時効処理を施した。これを比較例1とした。
磁石組成Iの焼結体加工品(10.1mm×10.1mm×4.2mm)に表3の拡散材8を塗布した。10.1mm×10.1mmの広い2面に均等に塗布し、2面の合計で5.5wt%とした。Ar雰囲気中で900℃6hの拡散熱処理を行い、塗布面の拡散材残渣をサンドペーパーで除去した。再度同じ量の拡散材8を塗布して同じくAr雰囲気中で900℃6時間の拡散熱処理を行い、塗布面の拡散材残渣を同様に除去した。さらに同量の拡散材8を塗布して900℃6時間の拡散熱処理を行った。すなわち、5.5wt%の拡散材8の塗布とAr中900℃6hの熱処理を3回繰り返した。次いでAr雰囲気中で540℃2時間の時効処理を行った。拡散材を塗布した面の拡散材の残渣をサンドペーパーで除去し、R-T-B系焼結磁石を得た。
磁石組成Iの焼結体加工品(10.1mm×10.1mm×4.2mm)に表3の3~7の拡散材を2面の合計で表3に示した量だけ10.1mm×10.1mmの広い2面に均等に塗布し、Ar雰囲気中で900℃6hの拡散熱処理を行った。熱処理後、拡散材塗布面の拡散材残渣をサンドペーパーで除去した。次いで拡散材2を2面の合計で4.5wt%塗布し同様にAr雰囲気中で900℃6hの熱処理を行った。熱処理後、サンドペーパーで塗布面の拡散材残渣を落とし、拡散材1を2面の合計で5.5wt%塗布して同様にAr雰囲気中で900℃6hの熱処理を行った。次いでAr雰囲気中で540℃2時間の時効処理を行った。拡散材塗布面の拡散材の残渣をサンドペーパーで除去し、R-T-B系焼結磁石を得た。最初の拡散熱処理で拡散材種を変えているが、拡散材3、4、5、6、7を用いた場合をそれぞれ実施例1、2、3、4、5とした。
磁石組成Iの焼結体加工品(10.1mm×10.1mm×4.2mm)に表3の拡散材3を10.1mm×10.1mmの2面に均等に両面の合計で3.8wt%塗布し、Ar雰囲気中で800℃10hの拡散熱処理を行った。熱処理後、拡散材塗布面の残渣をサンドペーパーで除去し、次いで拡散材2を4.5wt%塗布し同様にAr雰囲気中で800℃10hの熱処理を行った。熱処理後、サンドペーパーで塗布面の拡散材残渣を落とし、拡散材1を5.5wt%塗布して同様にAr雰囲気中で800℃10hの熱処理を行った。次いでAr雰囲気中で540℃2時間の時効処理を行った。拡散材塗布面の拡散材の残渣をサンドペーパーで除去し、R-T-B系焼結磁石を得た。
磁石組成Iの焼結体加工品(10.1mm×10.1mm×4.2mm)に表3の拡散材1を10.1mm×10.1mmの2面に均等に両面の合計で5.5wt%塗布し、Ar雰囲気中で900℃6hの拡散熱処理を行った。熱処理後、拡散材塗布面の残渣をサンドペーパーで除去し、次いで拡散材2を4.4wt%塗布し同様にAr雰囲気中で900℃6hの熱処理を行った。熱処理後、サンドペーパーで塗布面の拡散材残渣を落とし、拡散材3を5.4wt%塗布して同様にAr雰囲気中で900℃10hの熱処理を行った。次いでAr雰囲気中で540℃2時間の時効処理を行った。拡散材塗布面の拡散材の残渣をサンドペーパーで除去し、R-T-B系焼結磁石を得た。
粒界拡散法を用いた試料においては、Co、Cu、Mの増量が認められるが、塗布成分の原子比で7割以上を占めるNdの増加分はわずかである。これは焼結体内に含まれる粒界三重点および二粒子粒界部を含めた粒界のNd濃度が高く、焼結体内部に拡散するのに必要な濃度勾配が十分得られないためと考えられる。すなわち、このことから本発明はR量の増加によって特性を改善するものではない。
2 二粒子粒界部
2a、2b 境界
2c 二粒子粒界部の中点
3 粒界三重点
100 R-T-B系焼結磁石
10 SPMモータ
11 ハウジング
12 ロータ
13 ステータ
14 回転軸
15 ロータコア(鉄芯)
16 永久磁石
17 磁石挿入スロット
18 ステータコア
19 スロットル
20 コイル
Claims (4)
- R2T14B結晶粒とR2T14B結晶粒間の二粒子粒界部とを有するR-T-B系焼結磁石であって、R-Co-Cu-M-Fe相(M:Ga,Si,Sn,Ge,Biから選ばれる少なくとも1種)が形成する二粒子粒界部が存在することを特徴とするR-T-B系焼結磁石。
- 前記R-T-B系焼結磁石は、R-Co-Cu-M-Fe相が形成する二粒子粒界部とR-Cu-M-Fe相(M:Ga,Si,Sn,Ge,Biから選ばれる少なくとも1種)が形成する二粒子粒界部とを有し、R-Co-Cu-M-Fe相が形成する二粒子粒界部の数をA、R-Cu-M-Fe相が形成する二粒子粒界部の数をBで表すと、A>Bであることを特徴とする請求項1に記載のR-T-B系焼結磁石。
- 前記R-Co-Cu-M-Fe相(M:Ga,Si,Sn,Ge,Biから選ばれる少なくとも1種)が形成する二粒子粒界部の厚みが5~500nmであることを特徴とする請求項1または2に記載のR-T-B系焼結磁石。
- 請求項1~3のいずれかに記載されたR-T-B系焼結磁石を用いたモータ。
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