JP5902246B2 - permanent magnet - Google Patents

Description

  Embodiments described herein relate generally to a permanent magnet.

  As high performance permanent magnets, rare earth magnets such as Sm-Co magnets and Nd-Fe-B magnets are known. When a permanent magnet is used for a motor of a hybrid vehicle (HEV) or an electric vehicle (EV), the permanent magnet is required to have heat resistance. For a HEV or EV motor, a permanent magnet is used in which a portion of neodymium (Nd) in an Nd—Fe—B magnet is replaced with dysprosium (Dy) to improve heat resistance. Since Dy is one of rare elements, there is a demand for a permanent magnet with improved heat resistance without using Dy. Furthermore, in order to increase the efficiency of motors and generators, improvement in coercive force and magnetic flux density of permanent magnets is required.

Since Sm—Co magnets have a high Curie temperature, it is known that they exhibit excellent heat resistance in systems that do not use Dy. Sm—Co magnets are attracting attention as permanent magnets that can realize good motor characteristics and the like at high temperatures. Among Sm-Co magnets, especially Sm ₂ Co ₁₇ type magnets are expected as permanent magnets used in motors and generators because of their high coercive force and magnetic flux density. However, when conventional Sm ₂ Co _17- type magnets are applied to motors and generators, it is becoming clear that demagnetization tends to occur on the surface of the magnets when operating at high temperatures. For this reason, an Sm ₂ Co _17- type magnet that suppresses high-temperature demagnetization of the surface portion is required.

JP2011-216716A

  The problem to be solved by the present invention is to provide a permanent magnet that can suppress high-temperature demagnetization while maintaining the high coercive force and magnetic flux density of the Sm—Co magnet.

The permanent magnet of the embodiment is an R—Co-based (R is at least one element selected from rare earth elements) permanent magnet, and includes a magnet body and a surface portion provided so as to cover the entire surface of the magnet body. It comprises. The R concentration of the surface portion is higher than the R concentration of the magnet body.

It is sectional drawing which shows the permanent magnet by embodiment. It is a figure which shows a permanent magnet motor. It is a figure which shows a variable magnetic flux motor. It is a figure which shows a generator.

Hereinafter, the permanent magnet of the embodiment will be described. FIG. 1 is a cross-sectional view showing the configuration of the permanent magnet of the embodiment. A permanent magnet 1 shown in FIG. 1 includes a magnet body 2 and a surface portion 3 provided on the surface of the magnet body 2. The magnet body 2 has a composition represented by the following composition formula 1. The surface portion 3 has a composition represented by the following composition formula 2.
Composition formula 1: R (Fe _p1 M _{q1 Cur1} Co _1-p1-q1-r1 ) _z1
(In the formula, R represents at least one element selected from rare earth elements, M represents at least one element selected from Ti, Zr, and Hf, and p1, q1, r1, and z1 are each an atomic ratio of 0.8. 25 ≦ p1 ≦ 0.45, 0.01 ≦ q1 ≦ 0.05, 0.01 ≦ r1 ≦ 0.1, 6 ≦ z1 ≦ 9)
Composition formula 2: R (Fe _p2 M _{q2 Cur2} Co _1-p2-q2-r2 ) _z2
(In the formula, R represents at least one element selected from rare earth elements, M represents at least one element selected from Ti, Zr and Hf, and p2, q2, r2 and z2 are each an atomic ratio of 0. 25 ≦ p2 ≦ 0.45, 0.01 ≦ q2 ≦ 0.05, 0.01 ≦ r2 ≦ 0.1, 0.8 ≦ z2 / z1 ≦ 0.995)

  In the composition formula (1) and the composition formula (2), as the element R, at least one element selected from rare earth elements including yttrium (Y) is used. The element R brings a large magnetic anisotropy to the magnet material and imparts a high coercive force. The element R is preferably at least one selected from samarium (Sm), cerium (Ce), neodymium (Nd), and praseodymium (Pr), and particularly preferably Sm. By setting Sm to 50 atom% or more of the element R, the performance of the permanent magnet, particularly the coercive force, can be improved with good reproducibility. Furthermore, it is desirable that 70 atomic% or more of the element R is Sm.

  Iron (Fe) is mainly responsible for the magnetization of the permanent magnet. By blending a large amount of Fe, the saturation magnetization of the permanent magnet can be increased. However, if the Fe content becomes excessive, the coercive force decreases due to precipitation of the α-Fe phase. The Fe contents p1 and p2 in the composition formula (1) and the composition formula (2) are in the range of 0.25 to 0.45, respectively. By setting the Fe content p1, p2 to 0.25 or more, the saturation magnetization of the permanent magnet can be increased. The Fe contents p1 and p2 are preferably in the range of 0.28 to 0.40, and more preferably in the range of 0.30 to 0.36.

  As the element M, at least one element selected from titanium (Ti), zirconium (Zr), and hafnium (Hf) is used. By blending the element M, a large coercive force can be expressed with a composition having a high Fe concentration. The contents q1 and q2 of the element M in the composition formula (1) and the composition formula (2) are each in the range of 0.01 to 0.05. When q1 and q2 exceed 0.05, the magnetization is remarkably reduced, and when q1 and q2 are less than 0.01, the effect of increasing the Fe concentration is small. The contents M1 and q2 of the element M are preferably in the range of 0.01 to 0.03, and more preferably in the range of 0.015 to 0.25.

  The element M may be any of Ti, Zr, and Hf, but preferably contains at least Zr. In particular, the effect of increasing the coercive force of the permanent magnet can be improved by setting 50 atomic% or more of the element M to Zr. On the other hand, since Hf is particularly expensive among the elements M, it is preferable to reduce the amount used even when Hf is used. The Hf content is preferably less than 20 atomic% of the element M.

  Copper (Cu) is an essential element for allowing the Sm—Co permanent magnet to exhibit a high coercive force. The Cu contents r1 and r2 in the composition formulas (1) and (2) are each in the range of 0.01 to 0.1. When r1 and r2 exceed 0.1, the magnetization is remarkably reduced, and when r1 and r2 are less than 0.01, it is difficult to obtain a high coercive force. The Cu contents r1 and r2 are preferably in the range of 0.03 to 0.07, and more preferably in the range of 0.04 to 0.06.

  Cobalt (Co) is an element necessary for the magnetization of the permanent magnet and the high coercive force. Further, when a large amount of Co is contained, the Curie temperature is increased, and the thermal stability of the permanent magnet can be improved. If the Co content is too small, these effects cannot be obtained sufficiently. However, if the Co content is excessive, the Fe content is relatively reduced, which may cause a decrease in magnetization. Accordingly, the content of Co is determined so that the Fe contents p1 and p2 in the composition formula (1) and the composition formula (2) satisfy the above range after taking into account the contents of the elements R, M and Cu. Is set.

  A part of Co is nickel (Ni), vanadium (V), chromium (Cr), manganese (Mn), aluminum (Al), silicon (Si), gallium (Ga), niobium (Nb), tantalum (Ta), And at least one element A selected from tungsten (W) may be substituted. The substitution of Co by the element A may be applied to one of the composition formula (1) and the composition formula (2), or may be applied to both. The substitution element A contributes to improvement of magnet characteristics, for example, coercive force. However, since excessive substitution of Co with the element A may cause a decrease in magnetization, the substitution amount with the element A is preferably in the range of 20 atomic% or less of Co. In addition, the magnet material of the embodiment is allowed to contain inevitable impurities such as oxides.

  In the composition formula (1), the atomic ratio between the element R and the other elements (Fe, M, Cu, Co) is in the range of 1: 6 to 1: 9. That is, the value (atomic ratio) of z1 in the composition formula (1) is in the range of 6-9. If the value of z1 is less than 6, in other words, if the content ratio of the element R is too large, the magnetization is remarkably lowered, and a sufficient magnetic flux density cannot be obtained. If the value of z1 exceeds 9, in other words, if the content ratio of the element R is too small, a large amount of α-Fe phase is precipitated and a sufficient coercive force cannot be obtained. The value of z1 is more preferably in the range of 7.5 to 8.5, and still more preferably in the range of 7.7 to 8.3. The atomic ratio between the element R and other elements (Fe, M, Cu, Co) in the composition formula (2) will be described in detail later.

  The permanent magnet 1 of the embodiment is used in a state of being embedded in a motor or a generator after being processed into a rectangular parallelepiped shape, for example. In such a case, when the motor or the generator is exposed to a high temperature, magnetization reversal is likely to occur from the surface portion of the permanent magnet where the demagnetizing field is concentrated. When such high-temperature demagnetization occurs, the performance of the motor or generator is significantly reduced. In particular, since Sm—Co magnets contain highly volatile Sm, Sm evaporates from the surface of the magnet in the manufacturing process of the permanent magnet, which will be described later, and the Sm concentration in the surface may be smaller than that in the magnet. There is. The Sm—Co magnet is in a disadvantageous state for high temperature demagnetization because the Sm concentration of the surface portion is lowered.

  The present inventors have found that the high temperature demagnetization of the conventional Sm—Co based magnet is caused by the decrease in the concentration of the element R such as Sm in the surface portion described above. Therefore, in the permanent magnet 1 of the embodiment, the surface portion 3 having the composition represented by the composition formula 2 is provided on the surface of the magnet main body (inside the magnet) 2 having the composition represented by the composition formula 1. The composition of the surface portion 3 is characterized by the value of z2 indicating the atomic ratio of other elements (Fe, M, Cu, Co) to the element R. The value of z2 in the composition formula 2 is set so as to satisfy 0.8 ≦ z2 / z1 ≦ 0.995. By providing the surface portion 3 having such a composition satisfying z2 on the surface of the magnet body 2, high temperature demagnetization in the surface portion of the Sm—Co permanent magnet 1 can be suppressed.

  The ratio (z2 / z1) of the z2 value of the composition formula 2 to the z1 value of the composition formula 1 is less than 1, which means that the composition formula 2 is an element other than the element R (Fe, M) compared to the composition formula 1. , Cu, Co) means that the atomic ratio is small. That is, the surface portion 3 has a composition in which the content ratio of the element R is higher than that of the magnet body (inside the magnet) 2, in other words, a composition having a high concentration of the element R. Thus, by making the concentration of the element R in the surface portion 3 higher than that in the magnet body (inside the magnet) 2, the magnetization reversal of the surface portion 3 during operation at a high temperature and further the decrease in the magnetic flux based thereon are suppressed. can do. That is, high temperature demagnetization of the permanent magnet 1 can be suppressed. Accordingly, it is possible to provide the permanent magnet 1 capable of maintaining good characteristics even when it is incorporated in a motor or a generator and operated at a high temperature.

  In order to obtain an effect obtained by making the concentration of the element R in the surface portion 3 higher than that of the magnet body 2, the value of z2 in the composition formula 2 is set so that the z2 / z1 ratio is 0.995 or less. By setting the z2 / z1 ratio to 0.995 or less, high temperature demagnetization of the permanent magnet 1 can be effectively suppressed. In order to obtain a high-temperature demagnetization suppressing effect more effectively, the z2 / z1 ratio is preferably 0.95 or less. However, if the z2 / z1 ratio is too low, the concentration of the element R in the surface portion 3 becomes too high, and the magnetization of the surface portion 3 is significantly reduced. As a result, the magnetic flux density of the permanent magnet 1 as a whole is reduced and the magnet characteristics are deteriorated. For this reason, z2 / z1 ratio shall be 0.8 or more. The z2 / z1 ratio is preferably 0.85 or more.

  Here, if only the influence of the element R such as Sm evaporating from the magnet surface in the manufacturing process of the permanent magnet or the like is removed, the surface portion of the permanent magnet is ground at the time of use to remove the portion where the concentration of the element R is low. Remove it. However, excessive grinding of the permanent magnet reduces the yield and increases the manufacturing cost of the permanent magnet. Furthermore, the element R concentration in the surface portion cannot be made higher than that in the interior only by grinding the surface portion of the permanent magnet. By providing the surface portion 3 in which the concentration of the element R is higher than the inside 2 in advance for such a point, it is possible to suppress high temperature demagnetization of the permanent magnet 1 with good reproducibility. Further, the manufacturing cost can be reduced by reducing the grinding amount of the surface portion of the permanent magnet.

  It is preferable that the surface portion 3 in which the concentration of the element R is higher than that of the magnet body 2 is further lower than that of the magnet body 2. That is, the value of q2 in the composition formula 2 is preferably set so as to satisfy 0.5 ≦ q2 / q1 ≦ 0.95. By making the concentration of the element M on the surface portion 3 lower than that of the magnet body 2, the effect of suppressing the high temperature demagnetization of the permanent magnet 1 can be further enhanced. The composition region in which the concentration of the element M is lower than that of the magnet body 2 may be provided on the entire surface portion 3 or may be provided on a part of the surface portion 3. At least a part of the surface portion 3 preferably has a composition in which the value of q2 in the composition formula 2 satisfies 0.5 ≦ q2 / q1 ≦ 0.95.

  In order to obtain an effect of suppressing high temperature demagnetization by making the concentration of the element M in the surface portion 3 lower than that of the magnet body 2, the value of q2 in the composition formula 2 is set so that the q2 / q1 ratio is 0.95 or less. It is preferable to do. By setting the q2 / q1 ratio to 0.95 or less, the effect of suppressing the high temperature demagnetization of the permanent magnet 1 can be enhanced. In order to further enhance the effect of suppressing high temperature demagnetization, the q2 / q1 ratio is more preferably 0.9 or less. However, if the q2 / q1 ratio is too low, the α-Fe phase may precipitate on the surface portion 3 and the coercive force may decrease. For this reason, it is preferable that q2 / q1 ratio is 0.5 or more, More preferably, it is 0.7 or more.

  In the permanent magnet 1 of this embodiment, the magnet body (inside the magnet) 2 and the surface portion 3 are defined as follows. First, in the central part of the longest side of the surface having the maximum area of the permanent magnet 1, the composition of the inside and the surface part of the cross section cut perpendicular to the side (in the case of a curve, perpendicular to the tangent to the central part) is measured. . In the cross section, the measurement point is the reference line 1 drawn from the position of 1/2 of each side to the end perpendicular to the side and extending to the end, and the inner angle of the corner starting from the center of each corner. And a reference line 2 drawn inward toward the end at a position of ½ of the angle of the reference line 1, and the position of 1% of the length of the reference line from the starting point of the reference lines 1, 2 is the surface portion 3, 40. The% position is defined as internal 2. When a corner has a curvature due to chamfering or the like, an intersection of extending adjacent sides is defined as an end of the side (corner center). The measurement location is not from the intersection point, but from the portion in contact with the reference line.

  By setting the measurement locations as described above, for example, when the cross section is a quadrangle, the reference lines are 4 for the reference line 1 and the reference line 2 in total, and the measurement locations are the surface portion 3 and the interior 2. There are 8 places each. In this embodiment, it is preferable that all eight locations on the surface portion 3 and the interior 2 are within the composition range described above, but at least four locations on the surface portion 3 and the interior 2 are each within the composition range described above. That's fine. In this case, the relationship between the surface portion 3 and the interior 2 at one reference line is not defined. The composition analysis is performed, for example, by SEM-EDX (energy dispersive X-ray spectroscopy).

The permanent magnet of this embodiment is a phase-separated structure formed by using a TbCu ₇ type crystal phase (crystal phase having a TbCu ₇ type structure / 1-7 phase) as a precursor and subjecting it to an aging treatment or the like. That is, a cell phase composed of a Th ₂ Zn ₁₇ type crystal phase (a crystal phase having a Th ₂ Zn ₁₇ type structure / 2-17 phase) and a shape surrounding the cell phase, and a CaCu ₅ type crystal phase. It is preferable to have a metal structure having a cell wall phase composed of (crystalline phase having CaCu ₅ type structure / 1-5 phase). The metal structure of the permanent magnet may include a crystal phase or an amorphous phase other than the cell phase composed of 2-17 phase and the cell wall phase composed of 1-5 phase.

The domain wall energy of the 1-5 phase (cell wall phase) precipitated at the grain boundary of the 2-17 phase (cell phase) is larger than the domain wall energy of the 2-17 phase, and this domain wall energy difference is a barrier for domain wall movement. It becomes. In the Sm ₂ Co ₁₇ type magnet, it is considered that the domain wall pinning type coercive force is expressed by the 1-5 phase having a large domain wall energy acting as a pinning site. Here, it is considered that the domain wall energy difference is mainly caused by the Cu concentration difference. If the Cu concentration in the cell wall phase is higher than the Cu concentration in the cell phase, it is considered that coercive force appears. For this reason, it is preferable that the cell wall phase has a Cu concentration of 1.2 times or more the Cu concentration of the cell phase. Thereby, the cell wall phase can sufficiently function as a pinning site of the domain wall, and a sufficient coercive force can be obtained.

  As a typical example of the cell wall phase existing so as to surround the cell phase, the above-described 1-5 phase can be mentioned, but it is not necessarily limited thereto. When the cell wall phase has a Cu concentration of 1.2 times or more of the Cu concentration of the cell phase, the cell wall phase can sufficiently function as a pinning site of the domain wall, thereby obtaining a high coercive force. Is possible. Therefore, the cell wall phase may be a Cu-rich phase as described above. Examples of the cell wall phase other than the 1-5 phase include a 1-7 phase that is a high-temperature phase (structure before phase separation), a 1-5 phase precursor phase that occurs in the initial stage of phase separation of the 1-7 phase, and the like. Can be mentioned.

  The form of the permanent magnet of the embodiment is not necessarily limited, but is preferably a sintered magnet. The permanent magnet of the embodiment preferably has a magnet body (inside the magnet) 2 made of a sintered body having a composition represented by the composition formula (1), and a surface portion 3 provided on the surface thereof. The surface portion 3 may be formed at the same time as the magnet body 2 made of a sintered body, or may be formed by heat treatment or the like to be described later after the magnet body 2 made of a sintered body is formed. The formation method of the surface part 3 is not specifically limited, What is necessary is just to have a difference in the density | concentration of the element R between the magnet main bodies (magnet inside) 2, and also the density | concentration of the element M.

  The permanent magnet of this embodiment is produced as follows, for example. First, an alloy powder containing a predetermined amount of element is prepared. The alloy powder is prepared by, for example, grinding an alloy ingot obtained by casting a molten metal by an arc melting method or a high frequency melting method. The alloy powder may be prepared by pulverizing after producing a flaky alloy ribbon by a strip casting method. The alloy powder or the alloy before pulverization may be homogenized by heat treatment as necessary. Flakes and ingots are pulverized using a jet mill, a ball mill or the like. The pulverization is preferably performed in an inert gas atmosphere or an organic solvent in order to prevent oxidation of the alloy powder.

  Next, an alloy powder is filled in a metal mold placed in an electromagnet or the like, and pressure forming is performed while applying a magnetic field, thereby producing a green compact with the crystal axis oriented. A dense sintered body can be obtained by sintering the green compact under appropriate conditions. The sintering temperature is preferably in the range of 1100 to 1300 ° C, and the sintering time is preferably in the range of 0.5 to 15 hours. The green compact is preferably sintered in vacuum or in an inert gas atmosphere such as argon gas in order to prevent oxidation.

  Next, a solution treatment and an aging treatment are performed on the obtained sintered body to control the crystal structure. The solution treatment is a treatment for obtaining the 1-7 phase which is a precursor of the phase separation structure, and is preferably carried out by holding at a temperature in the range of 1110 to 1200 ° C. for 0.5 to 8 hours. The aging treatment is a treatment for controlling the crystal structure and increasing the coercive force of the magnet. The aging treatment is held at a temperature of 700 to 900 ° C. for 0.5 to 80 hours, and then gradually cooled to a temperature of 400 to 650 ° C. at a cooling rate of 0.2 to 2 ° C./min, and subsequently cooled to room temperature. It is preferable to implement by. The solution treatment and aging treatment are preferably performed in vacuum or in an inert gas atmosphere such as argon gas in order to prevent oxidation.

  The permanent magnet (sintered magnet) obtained by the manufacturing method described above has a single composition as in the case of the conventional Sm-Co magnet. Next, a method for providing a concentration difference between the element R and the element M between the magnet body (inside) 2 and the surface portion 3 will be described. As a method for providing the concentration difference of the element R, the method of diffusing the element R by heat treatment after vaporizing the element R on the surface of the sintered body is effective. When Sm is used as the element R, Sm has a high vapor pressure at a high temperature. Therefore, Sm can be deposited on the surface of the sintered body by arranging a powder having a high Sm concentration around the sintered body. . Further, after applying compound powder such as fluoride or oxide containing element R to the surface of the sintered body, the element R may be diffused by heat treatment.

  The heat treatment performed after the deposition of the element R or after the application of the compound powder containing the element R is performed under such conditions that the element R is sufficiently diffused from the surface of the sintered body and a compound having a high concentration of the element R is generated. It is preferable to implement. The heat treatment is preferably performed, for example, at a temperature of 500 to 1000 ° C. for 0.1 to 10 hours. Thereby, the surface part 3 which has a composition whose z2 / z1 ratio is the range of 0.8-0.995 can be provided in the surface of the magnet main body 2 which consists of a sintered compact. If the heat treatment temperature and heat treatment time are insufficient, the diffusion and compounding of the element R cannot be sufficiently advanced, and the z2 / z1 ratio of the surface portion 3 cannot be controlled within a predetermined range.

  Examples of the method for imparting the concentration difference of the element M include a method in which a plurality of alloy powders having different concentrations of the element M are sequentially put into a mold and pressure-molded in a step of producing a green compact. For example, an alloy powder 1 having an element M content within a predetermined range and an alloy powder 2 having an element M content lower than that of the alloy powder 1 are prepared. First, the alloy powder 2 is charged into the mold, then the alloy powder 1 is charged, and finally the alloy powder 2 is charged again. By compacting in this state, a green compact in which portions having a low concentration of element M are provided on both the upper and lower surfaces is obtained. By forming such a green compact under pressure, a sintered body in which the surface portion 3 having a low concentration of the element M is provided on the surface of the magnet body 2 having a predetermined concentration of the element M can be obtained.

  A sintered body having a concentration difference of the element R and a concentration difference of the element M can be obtained by combining the methods described above. Further, by adjusting the heat treatment conditions performed after the deposition of the element R or after the application of the compound powder containing the element R, the concentration difference of the element M can be given simultaneously with the concentration difference of the element R. The method described here is an example, and by either method, a sintered body in which the concentration difference of the element R is generated between the inside and the surface portion, and further, a sintered body in which the concentration difference of the element M is generated is obtained. It only has to be done. And by giving the solution treatment and aging treatment which were mentioned above to such a sintered compact, it has the magnet main body (inside) 2 and the surface part 3 from which a composition differs, maintaining a high coercive force and magnetic flux density. The permanent magnet 1 is obtained. The solution treatment may be performed in advance before the processing for imparting a concentration difference between the element R and the element M is performed.

  The permanent magnet of this embodiment can be used for various motors and generators. Further, it can be used as a fixed magnet or a variable magnet of a variable magnetic flux motor or a variable magnetic flux generator. Various motors and generators are configured by using the permanent magnet of this embodiment. When the permanent magnet of this embodiment is applied to a variable magnetic flux motor, the technology disclosed in Japanese Patent Application Laid-Open Nos. 2008-29148 and 2008-43172 is applied to the configuration and drive system of the variable magnetic flux motor. be able to.

  Next, a motor and a generator to which the permanent magnet of the embodiment is applied will be described with reference to the drawings. FIG. 2 shows a permanent magnet motor to which the permanent magnet of the embodiment is applied. In the permanent magnet motor 11 shown in FIG. 2, a rotor (rotor) 13 is disposed in a stator (stator) 12. In the iron core 14 of the rotor 13, the permanent magnet 15 of the embodiment is disposed. Based on the characteristics and the like of the permanent magnet of the embodiment, the permanent magnet motor 11 can be made highly efficient, downsized, reduced in cost, and the like.

  FIG. 3 shows a variable magnetic flux motor to which the permanent magnet of the embodiment is applied. In the variable magnetic flux motor 21 shown in FIG. 3, a rotor (rotor) 23 is disposed in a stator (stator) 22. In the iron core 24 of the rotor 23, the permanent magnets of the embodiment are arranged as a fixed magnet 25 and a variable magnet 26. The variable magnet 26 can change the magnetic flux density (the amount of magnetic flux). Since the magnetization direction of the variable magnet 26 is perpendicular to the Q-axis direction, the variable magnet 26 can be magnetized by the D-axis current without being affected by the Q-axis current. The rotor 23 is provided with a magnetized winding (not shown). By passing a current from the magnetization circuit through the magnetization winding, the magnetic field directly acts on the variable magnet 26.

  According to the permanent magnet of the embodiment, by changing the various conditions of the manufacturing method described above, for example, a fixed magnet 25 having a coercive force exceeding 500 kA / m and a variable magnet 26 having a coercive force of 500 kA / m or less are obtained. Can do. In the variable magnetic flux motor 21 shown in FIG. 3, the permanent magnet of the embodiment can be used for both the fixed magnet 25 and the variable magnet 26, but the permanent magnet of the embodiment is used for either one of the magnets. It may be used. Since the variable magnetic flux motor 21 can output a large torque with a small device size, the variable magnetic flux motor 21 is suitable for a motor such as a hybrid vehicle or an electric vehicle that requires a high output and a small size of the motor.

  FIG. 4 shows a generator to which the permanent magnet of the embodiment is applied. A generator 31 shown in FIG. 4 includes a stator (stator) 32 using the permanent magnet of the embodiment. A rotor (rotor) 33 disposed inside the stator (stator) 32 is connected to a turbine 34 provided at one end of the generator 31 via a shaft 35. The turbine 34 is rotated by a fluid supplied from the outside, for example. Note that the shaft 35 can be rotated by transmitting dynamic rotation such as regenerative energy of the automobile instead of the turbine 34 rotated by the fluid. Various known configurations can be employed for the stator 32 and the rotor 33.

  The shaft 35 is in contact with a commutator (not shown) disposed on the side opposite to the turbine 34 with respect to the rotor 33, and an electromotive force generated by the rotation of the rotor 33 is used as an output of the generator 31 as a phase separation bus. The power is boosted to the system voltage and transmitted through a main transformer (not shown). The generator 31 may be either a normal generator or a variable magnetic flux generator. Note that the rotor 33 is charged by static electricity from the turbine 34 or shaft current accompanying power generation. For this reason, the generator 31 includes a brush 36 for discharging the charging of the rotor 33.

  Next, examples and evaluation results thereof will be described.

(Examples 1-8)
Each raw material was weighed and mixed at a predetermined ratio, and then arc-melted in an Ar gas atmosphere to produce an alloy ingot. The alloy ingot was coarsely pulverized and then finely pulverized with a jet mill to prepare an alloy powder. Next, the alloy powder is pressed into a green compact in a magnetic field, sintered at 1200 ° C. for 2 hours in an Ar gas atmosphere, and subsequently held at 1130 ° C. for 3 hours for solution treatment. Thus, a sintered body was produced.

  Next, after vapor-depositing Sm on the surface of the obtained sintered body, heat treatment is performed by holding at 700 ° C. for 1 hour in an Ar gas atmosphere, so that Sm is diffused from the surface and between the inside and the surface portion. Was given a difference in Sm concentration. The deposition of Sm on the surface of the sintered body was performed by a physical vapor deposition method in which an Sm metal powder having a particle size of 250 μm or less was heated and evaporated, and this Sm vapor was adsorbed on the surface of the sintered body. Thus, the sintered compact which provided the Sm density | concentration difference between the inside and the surface part was hold | maintained at 790 degreeC in Ar gas atmosphere for 4 hours, Then, it cooled gradually to 400 degreeC, and also cooled to room temperature. The sintered magnet thus obtained was subjected to the characteristic evaluation described later.

(Comparative Example 1)
A sintered magnet was produced in the same manner as in Example 1 except that the deposition of Sm on the surface of the sintered body and the subsequent heat treatment were not performed. The obtained sintered magnet was subjected to the characteristic evaluation described later.

(Comparative Example 2)
After depositing Sm on the surface of the sintered body, a sintered magnet was produced in the same manner as in Example 1 except that heat treatment was performed by holding at 400 ° C. for 1 hour in an Ar gas atmosphere. The obtained sintered magnet was subjected to the characteristic evaluation described later.

  The compositions of the interior and surface portions of the sintered magnets of Examples 1 to 8 and Comparative Examples 1 and 2 described above were measured by the method described above. The composition analysis was performed on the four internal parts and the four surface parts, and the average values thereof are shown in Table 1 as the internal composition and the surface part composition. Next, the magnetic properties of the sintered magnet at room temperature were evaluated with a BH tracer, and coercive force and remanent magnetization were measured. Furthermore, the sintered magnet was embedded in the IPM motor, and the demagnetization state at 150 ° C. was examined. These results are shown in Table 2. The evaluation result of the demagnetization state at 150 ° C. indicates that the demagnetization region exceeding 5% is confirmed, x indicates that the demagnetization region exceeding 5% is not confirmed, ○ ○ demagnetization region exceeding 1% Those that were not confirmed were shown as ◎.

  As can be seen from Table 2, it can be seen that all of the sintered magnets of Examples 1 to 8 are excellent in magnetic properties and the occurrence of high temperature demagnetization is suppressed. On the other hand, in the sintered magnet of Comparative Example 1, generation of a demagnetization region up to about 5% was observed at the corners. In the sintered magnet of Comparative Example 2, although the occurrence of high temperature demagnetization is suppressed, since the heat treatment conditions after the deposition of Sm are insufficient, the Sm concentration in the surface portion becomes too high, resulting in a decrease in residual magnetization. Was recognized.

(Examples 9 to 13)
Each raw material was weighed and mixed at a predetermined ratio, and then arc-melted in an Ar gas atmosphere to produce an alloy ingot. The alloy ingot was coarsely pulverized and then finely pulverized with a jet mill to prepare an alloy powder 1. Further, an alloy powder 2 having a low Zr concentration was prepared in the same manner. Alloy powder 2 was charged into the mold, then alloy powder 1 was charged, and finally, alloy powder 2 was charged again, followed by press molding in a magnetic field to obtain a green compact. The green compact was sintered in an Ar gas atmosphere by holding at 1200 ° C. for 2 hours, and subsequently held at 1130 ° C. for 3 hours to produce a sintered body.

  Next, after vapor-depositing Sm on the surface of the obtained sintered body, heat treatment is performed by holding it at 900 ° C. for 1 hour in an Ar gas atmosphere, thereby diffusing Sm from the surface so that the space between the inside and the surface portion Was given a difference in Sm concentration. The deposition of Sm on the surface of the sintered body was performed by a physical vapor deposition method in which an Sm metal powder having a particle size of 250 μm or less was heated and evaporated, and this Sm vapor was adsorbed on the surface of the sintered body. The sintered body thus imparted with the Sm concentration difference and the Zr concentration difference between the inside and the surface portion was held at 790 ° C. for 4 hours in an Ar gas atmosphere and then gradually cooled to 400 ° C. Cooled to room temperature. The sintered magnet thus obtained was subjected to characteristic evaluation.

  The composition of the inside and surface portion of the sintered magnets of Examples 9 to 13 described above was measured by the method described above. The composition analysis was performed on the four internal portions and the four surface portions, and the average values thereof are shown in Table 3 as the internal composition and the surface portion composition. Next, the magnetic properties of the sintered magnet at room temperature were evaluated with a BH tracer, and coercive force and remanent magnetization were measured. Furthermore, the sintered magnet was embedded in the IPM motor, and the demagnetization state at 150 ° C. was examined. These results are shown in Table 4. The evaluation result of the demagnetization state at 150 ° C. is based on the same evaluation criteria as in Table 1.

  In addition, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Permanent magnet, 2 ... Magnet main body (inside), 3 ... Surface part, 11 ... Permanent magnet motor, 12 ... Stator, 13 ... Rotor, 14 ... Iron core, 15 ... Permanent magnet, 21 ... Variable magnetic flux motor, 22 ... Stator , 23 ... rotor, 24 ... iron core, 25 ... fixed magnet, 26 ... variable magnet, 31 ... variable magnetic flux generator, 32 ... stator, 33 ... rotor, 34 ... turbine, 35 ... shaft.

Claims (6)

R-Co-based (R is at least one element selected from rare earth elements) permanent magnets,
Comprising a magnet body and a surface portion provided so as to cover the entire surface of the magnet body;
The R concentration of the surface portion is a permanent magnet higher than the R concentration of the magnet body. The permanent magnet according to claim 1,
A permanent magnet in which 50 atomic% or more of the element R is Sm. The permanent magnet according to claim 1,
The magnet body is
Composition formula 1: R (Fe _p1 M _{q1 Cur1} Co _1-p1-q1-r1 ) _z1
(In the formula, R is selected from rare earth elements and at least one element in which 50 atomic% or more is Sm, M represents at least one element selected from Ti, Zr and Hf, and p1, q1, r1 and z1 is an atomic ratio, and is a number satisfying 0.25 ≦ p1 ≦ 0.45, 0.01 ≦ q1 ≦ 0.05, 0.01 ≦ r1 ≦ 0.1, and 6 ≦ z1 ≦ 9)
The permanent magnet which has a composition represented by these. The permanent magnet according to claim 3,
The magnet body is a permanent magnet comprising a sintered body having a cell phase consisting of Th ₂ Zn ₁₇ crystal phase, a metal structure having a cell wall phase present so as to surround the cell phase. The permanent magnet according to claim 3 or claim 4,
A permanent magnet in which 50 atomic% of the element M in the composition formula 1 is Zr. The permanent magnet according to any one of claims 3 to 5,
A permanent magnet in which 20 atomic% or less of Co in the composition formula 1 is substituted with at least one element A selected from Ni, V, Cr, Mn, Al, Ga, Nb, Ta and W.

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