R-T-B based sintered magnet and motor

Abstract

The present invention provides an R-T-B based sintered magnet that inhibits the demagnetization rate at high temperature even when less or no heavy rare earth elements such as Dy, Tb and the like are used. The R-T-B based sintered magnet includes R.sub.2T.sub.14B crystal grains and two-grain boundary parts between the R.sub.2T.sub.14B crystal grains. Two-grain boundary parts formed by RCoCu-M-Fe phase exist, and M is at least one selected from the group consisting of Ga, Si, Sn, Ge and Bi.

Claims

1. An R-T-B based sintered magnet comprising R.sub.2T.sub.14B crystal grains and two-grain boundary parts between the R.sub.2T.sub.14B crystal grains, wherein said R-T-B based sintered magnet comprises the two-grain boundary parts formed by RCoCu-M-Fe phase and two-grain boundary parts formed by RCu-M-Fe phase, and M is at least one selected from the group consisting of Ga, Si, Sn, Ge and Bi, the content of Co relative to the total mass of the R-T-B based sintered magnet is 0.4 mass % or more and 3.0 mass % or less, and A is more than B, wherein the number of the two-grain boundary parts formed by RCoCu-M-Fe phase is represented by A and the number of the two-grain boundary parts formed by RCu-M-Fe phase is represented by B.

2. A motor comprising the R-T-B based sintered magnet according to claim 1.

3. The R-T-B based sintered magnet according to claim 1, wherein the thickness of the two-grain boundary parts formed by RCoCu-M-Fe phase is 5500 nm.

4. A motor comprising the R-T-B based sintered magnet according to claim 3.

5. The R-T-B based sintered magnet according to claim 1, wherein M is at least Ga.

6. The R-T-B based sintered magnet according to claim 1, wherein M is at least Si.

7. The R-T-B based sintered magnet according to claim 1, wherein M is at least Sn.

8. The R-T-B based sintered magnet according to claim 1, wherein M is at least Ge.

9. The R-T-B based sintered magnet according to claim 1, wherein M is at least Bi.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view schematically representing the main phase crystal grains and the two-grain boundary parts of the R-T-B based sintered magnet according to the present invention.

(2) FIG. 2 is schematic drawing describing a composition analysis point of the two-grain boundary part and the method for measuring the width of the two-grain boundary parts.

(3) FIG. 3 is a cross-sectional view briefly showing the structure of a motor according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

(4) Hereinafter, the preferred embodiments of the present invention are illustrated while making a reference to the drawings. In addition, the R-T-B based sintered magnet as mentioned in this invention refers to a sintered magnet containing R.sub.2T.sub.14B main phase crystal grains and two-grain boundary parts, and in the sintered magnet, R contains one or more rare earth elements, T contains one or more iron group elements with Fe as an essential element, B is contained, furthermore a sintered magnet added with various well-known additive elements are included.

(5) FIG. 1 is a view schematically representing the cross-section structure of the R-T-B based sintered magnet of an embodiment according to the present invention. The R-T-B based sintered magnet according to this embodiment at least contains R.sub.2T.sub.14B main phase crystal grains 1, and two-grain boundary parts 2 formed between adjacent R.sub.2T.sub.14B main phase crystal grains 1.

(6) The R-T-B based sintered magnet of the present embodiment is characterized in that the two-grain boundary parts formed by RCoCu-M-Fe phases (M is at least one selected from the group consisting of Ga, Si, Sn, Ge, and Bi) exist. In addition, the R-T-B based sintered magnet mentioned above has the two-grain boundary parts formed by the RCoCu-M-Fe phases and the two-grain boundary parts formed by RCu-M-Fe phases (M is at least one selected from the group consisting of Ga, Si, Sn, Ge, and Bi). If the number of the two-grain boundary parts formed by RCoCu-M-Fe phases is represented by A and the number of the two-grain boundary parts formed by RCu-M-Fe phases is represented by B, it is preferable that A>B. Further, the thickness of the two-grain boundary parts formed by the RCoCu-M-Fe phases (M is at least one selected from the group consisting of Ga, Si, Sn, Ge, and Bi) is preferred to be 5500 nm.

(7) FIG. 2 is schematic drawing describing the method for measuring the width and the composition of the two-grain boundary parts of the present embodiment. The two-grain boundary parts 2 and the grain boundary triple junction 3 are formed between the adjacent R.sub.2T.sub.14B main phase crystal grains. Focusing on one two-grain boundary part 2 as the measuring object, the boundaries 2a, 2b between this two-grain boundary part and the grain boundary triple junction 3 connecting thereto are determined. The vicinities of the boundaries 2a, 2b are not to be measured, and thus high accuracy is not a necessity. The interval between the boundaries 2a and 2b is quadrisected and three quadrisectors are drawn. The positions of the three quadrisectors are taken as points for determining the width of the two-grain boundary phases, yielding measured values of three points. Said determination is conducted to the 20 two-grain boundary parts arbitrarily selected to be focused on, and the thickness (width) of the total 60 measuring points is measured.

(8) Moreover, in the 20 two-grain boundary parts, the composition analysis is conducted at the midpoint 2c on the line obtained by dividing boundaries 2a, 2b in half in the width direction of the two-grain boundary part. After composition analysis is carried out, phases are categorized and then accumulated. The compositions of the grain boundary phases exist in the two-grain boundary parts are categorized according to the composition features of each phase described as follows. Firstly, the composition feature of the RCoCu-M-Fe phases is that the total content of R is 4070 atomic %, Co is contained with the content of 110 atomic %, Cu is contained with the content of 550 atomic %, M is contained with the content of 115 atomic %, and Fe is contained with the content of 140 atomic %. The composition feature of the RCu-M-Fe phases is that the total content of R is 1020 atomic %, Co is contained with the content of lower than 0.5 atomic %, Cu is contained with the content of lower than 1 atomic %, M is contained with the content of 110 atomic %, and Fe is contained with the content of 6590 atomic %.

(9) Beside the RCoCu-M-Fe phases and the RCu-M-Fe phases, R.sub.6T.sub.13M phases and R phases may be contained in the two-grain boundary parts of the present embodiment. R.sub.6T.sub.13M phases are characterized in that the total content of R is 2630 atomic %, Co is contained with the content of lower than 2 atomic %, M is contained with the content of 110 atomic %, balance amount of Fe is contained and the other elements are contained with the content of 6070 atomic %. R phases are characterized in that the total content of R is 90 atomic % or more.

(10) Even if a phase contains the elements purposefully added in the R-T-B based sintered magnet or unavoidable impurities with a small amount such as less than several % beside the above constituent element, it also can be categorized according to the features mentioned above. Despite this, the phase which is not corresponding to any one of the phases mentioned above can be treated as the other phase.

(11) In the R.sub.2T.sub.14B main phase crystal grains composing the R-T-B based sintered magnet according to this embodiment, as the rare earth R, it may be any one of a light rare-earth element, a heavy rare-earth element, or a combination of both, and Nd, Pr or the combination thereof is preferred from the viewpoint of material costs. As the iron group element T, Fe or the combination of Fe and Co is preferred, but is not limited thereto. In addition, B represents boron. In the R-T-B based sintered magnet of this embodiment, the contents of the elements relative to the total mass are shown as follows. In addition, mass % is regarded as the same unit with weight % in the present specification.

(12) R: 25 to 35 mass %;

(13) B: 0.5 to 1.5 mass %;

(14) M: 0.01 to 1.5 mass %;

(15) Cu: 0.01 to 1.5 mass %;

(16) Co: 0.3 to 3.0 mass %;

(17) Al: 0.03 to 0.6 mass %;

(18) Fe: balance, substantially; and

(19) The total content of elements other than Fe occupying the balance: 5 mass % or lower.

(20) Hereinafter, it is more preferable as follows.

(21) R: 29.5 to 33.1 mass %;

(22) B: 0.75 to 0.95 mass %;

(23) M: 0.01 to 1.0 mass %;

(24) Cu: 0.01 to 1.5 mass %;

(25) Co: 0.3 to 3.0 mass %;

(26) Al: 0.03 to 0.6 mass %;

(27) Fe: balance, substantially; and

(28) The total content of elements other than Fe occupying the balance: 5 mass % or lower.

(29) If the content of each element falls within the above range, the RCoCu-M-Fe phases are easily formed.

(30) Hereinafter, more detailed description is provided on conditions such as contents of the elements or atomic ratios.

(31) The content of R in the R-T-B based sintered magnet according to the present embodiment is 25 to 35 mass %. In the case that a heavy rare earth element is contained as R, the total content of rare earth elements including the heavy rare earth element is within said range. A heavy rare earth element refers to an element with a larger atom number among the rare earth elements, and generally, rare earth elements from 64Gd to 71Lu correspond to said heavy rare earth elements. If the content of R is within said range, it tends to get a high residual magnetic flux density and coercivity. If the content of R is lower than said range, it will be hard to form the R.sub.2T.sub.14B phase as the main phase, and it is easy to form a -Fe phase with soft magnetism, and consequently, the coercivity is decreased. In another aspect, if the content of R is larger than said range, the volume percentage of the R.sub.2T.sub.14B phase becomes lower, and the residual magnetic flux density is reduced. In addition, in the sintering step of the production process, the sintering starting temperature extremely reduces, and the grain growth becomes easier. The more preferable range of the content of R is 29.5 to 33.1 mass %.

(32) As R, either of Nd and Pr must be contained, and the ratio of Nd and Pr (calculated by a total of Nd and Pr) in R can be 80 to 100 atomic %, and it is more preferred to be 95 to 100 atomic %. If within such a range, a more favorable residual magnetic flux density and coercivity can be obtained. As set forth above, the R-T-B based sintered magnet may also contain Dy, Tb, Ho and the like heavy rare earth elements as R, and in this situation, the content of heavy rare earth elements (calculated as the total of heavy rare earth elements) in total mass of the R-T-B based sintered magnet is 1.0 mass % or less, more preferably 0.5 mass % or less, further preferably 0.1 mass % or less. If it is an R-T-B based sintered magnet of the present embodiment, even the contents of heavy rare earth elements are reduced like this, a favorable and high coercivity can still be obtained by rendering contents of other elements and the atomic ratios satisfying certain requirements.

(33) The R-T-B based sintered magnet according to the present embodiment contains B. The content of B is 0.5 mass % or more and 1.5 mass % or less, preferably 0.7 mass % or more and 1.2 mass % or less, more preferably 0.75 mass % or more and 0.95 mass % or less. If the content of B is less than 0.5 mass %, the coercivity HcJ tends to reduce. Moreover, if the content of B is over 1.5 mass %, the residual magnetic flux density Br tends to decrease. Especially, when the content of B falls within the range of 0.75 mass % or more and 0.95 mass % or less, RCoCu-M-Fe phases are easily formed.

(34) The R-T-B based sintered magnet according to the present embodiment contains Co. The content of Co is preferably 0.3 mass % or more and 3.0 mass % or less. The added Co exists in any one of the main phase crystal grains, triple junctions and the two-grain boundary parts. It reads to the increase of the Curie temperature and the improvement of the corrosion resistance of the grain boundary phases. Further, the demagnetization at high temperature can be inhibited by forming the two-grain boundary parts with the RCoCu-M-Fe phases. Co can be added during preparing the alloys, and Co also can be diffused in the sintered body alone or together with Cu, M and the like through grain boundary diffusion mentioned below and thus Co can be contained.

(35) The R-T-B based sintered magnet according to the present embodiment contains Cu. The addition amount of Cu is preferably 0.01 to 1.5 mass % in the whole magnet, more preferably 0.05 to 1.5 mass %. By making the addition amount within this range, Cu can be unevenly distributed in the triple junctions and the two-grain boundary parts. Cu which is unevenly distributed in the triple junctions and the two-grain boundary parts is helpful to form the RCoCu-M-Fe phases, and thus demagnetization at high temperature can be inhibited. Cu can be added during preparing the alloys, and Cu also can be diffused in the sintered body alone or together with Co, M and the like through grain boundary diffusion mentioned below and thus Cu can be contained.

(36) The R-T-B based sintered magnet according to the present embodiment further contains M. M represents at least one selected from the group consisting of Ga, Si, Sn, Ge and Bi. By containing M, the RCoCu-M-Fe phases of the two-grain boundary parts can be easily formed. The content of M is preferably 0.01 to 1.5 mass %. If the content of M is less than this range, the suppression of demagnetization at high temperature becomes insufficient. Even if the content is more than the range, not only demagnetization at high temperature will not be further improved, but also saturation magnetization reduces, and thus the residual magnetic flux density is insufficient. In order to achieve a high suppression of demagnetization at high temperature and a high residual magnetic flux density, the content of M is further preferably 0.1 to 1.0 mass %. M can be added during preparing the alloys, and M also can be diffused in the sintered body alone or together with Co, Cu and the like through grain boundary diffusion mentioned below and thus M can be contained. M is particularly preferably Ga.

(37) The R-T-B based sintered magnet according to the present embodiment preferably contains Al. The obtained magnet can get a high coercivity, a high corrosion resistance, and an improved temperature performance by containing Al. The content of Al is preferably 0.03 mass % or more and 0.6 mass % or less, and more preferably 0.05 mass % or more and 0.25 mass % or less.

(38) The R-T-B based sintered magnet according to the present embodiment contains Fe and the other elements beside the above mentioned elements. Fe and the other elements occupy the balance other than the total contents of the above elements in the total mass of the R-T-B based sintered magnet. However, in order to allow the R-T-B based sintered magnet functions sufficiently as a magnet, among the elements occupying the balance, the total content of elements other than Fe is preferably 5 mass % or less relative to the total mass of the R-T-B based sintered magnet.

(39) In addition, the content of C in the R-T-B based sintered magnet according to the present embodiment is 0.05 to 0.3 mass %. If the content of C is lower than said range, the residual magnetic flux density will be insufficient. And, if larger than said range, the ratio of the magnetic field value (Hk) when the magnetization is 90% of residual magnetic flux density, with respect to coercivity, i.e. the squareness ratio (Hk/HcJ) becomes insufficient. In order to obtain the coercivity and the squareness ratio better, the content of C may also be 0.1 to 0.25 mass %.

(40) In addition, the content of 0 in the R-T-B based sintered magnet according to the present embodiment is 0.05 to 0.25 mass %. If the content of O is lower than said range, the corrosion resistance of the R-T-B based sintered magnet will be insufficient. And, if it is larger than said range, a liquid phase cannot be sufficiently formed in the R-T-B based sintered magnet and the coercivity will decrease. In order to obtain the corrosion resistance and the coercivity better, the content of O is more preferably 0.05 to 0.20 mass %.

(41) In the R-T-B based sintered magnet according to the present embodiment, for example, Zr may be contained as the other element. In this situation, the content of Zr in total mass of the R-T-B based sintered magnet is preferably 0.01 to 1.5 mass %. Zr may inhibit the abnormal growth of crystal grains during the production of the R-T-B based sintered magnet, rendering the structure of the obtained sintered body (the R-T-B based sintered magnet) uniform and fine, which may improve the magnetic characteristic.

(42) Moreover, the R-T-B based sintered magnet according to the present embodiment may contain 0.001 to 0.5 mass % of inevitable impurities like Mn, Ca, Ni, Cl, S, F and the like as the constituent elements other than above.

(43) In addition, in the R-T-B based sintered magnet according to the present embodiment, the content of N is preferably 0.15 mass % or less. If the content of N is larger than said range, the coercivity tends to become insufficient.

(44) An example of the method for producing the R-T-B based sintered magnet according to the present embodiment is described. The R-T-B based sintered magnet according to this embodiment may be produced by a conventional powder metallurgic method comprising a confecting process of confecting the raw material alloys, a pulverizing process of pulverizing the raw material alloys into fine powder raw materials, a pressing process of pressing the fine powder raw materials into a green compact, a sintering process of sintering the green compact into a sintered body, and a heat treating process of subjecting the sintered body to an aging treatment.

(45) The confecting process is a process for confecting the raw material alloys that contain respective elements contained in the R-T-B based sintered magnet according to this embodiment. Firstly, the raw metals having the specified elements are prepared, and subjected to a strip casting method and the like. The raw material alloys are thus confected. As the metal raw materials, for examples, rare earth metals or rare earth alloys, pure iron, pure cobalt, ferroboron or alloys thereof can be exemplified. These metal raw materials are used to confect the raw material alloys of the R-T-B based sintered magnet having the desired composition. Alternatively, two kinds of alloys, i.e., the first alloy whose composition is close to R.sub.2T.sub.14B, and the second alloy mainly increasing R or the content of the additives, can be produced respectively, and then mixed before or after the fine pulverizing process. In addition, the alloy with R or the content of the additives increased whose composition is different from that of the second alloy is used as the third alloy, and the alloy with R or the content of the additives increased whose composition is different from those of the second alloy and the third alloy is used as the fourth alloy, and they are mixed with the first alloy before or after the fine pulverizing process. In order to promote the formation of the RCoCu-M-Fe phases in the grain boundary, eutectic alloys, such as 80% Nd-20% Co, 70Nd-30% Cu, 80% Nd-20% Ga calculated with atomic %, are used as the second alloy, the third alloy, the fourth alloy, and mixed with the first alloy.

(46) The pulverizing process is a process for pulverizing the raw material alloys obtained in the confecting process into fine powder raw materials. This process is preferably performed in two stages comprising a coarse pulverization and a fine pulverization, and may also be performed as one stage. The coarse pulverization may be performed by using, for example, a stamp mill, a jaw crusher, a braun mill, etc under an inert atmosphere. A hydrogen decrepitation in which pulverization is performed after hydrogen adsorption may also be performed. In the coarse pulverization, the raw material alloys are pulverized until the particle size is around several hundreds of micrometers to several millimeters.

(47) The fine pulverization finely pulverizes the coarse powder obtained in the coarse pulverization, and prepares the fine powder raw materials with the average particle size of several micrometers. The average particle size of the fine powder raw materials may be set under the consideration of the growth of the crystal grains after sintering. For example, the fine pulverization may be performed by a jet mill.

(48) The pressing process is a process for pressing the fine powder raw materials into a green compact in the magnetic field. Specifically, after the fine powder raw materials are filled into a press mold equipped in an electromagnet, the pressing is performed by orientating the crystallographic axis of the fine powder raw materials by applying a magnetic field via the electromagnet, while pressurizing the fine powder raw materials. The pressing may be performed in a magnetic field of 10001600 kA/m under a pressure of 30300 MPa.

(49) The sintering process is a process for sintering the green compact into a sintered body. After being pressed in the magnetic field, the green compact may be sintered in a vacuum or an inert atmosphere to obtain a sintered body. Preferably, the sintering conditions are suitably set depending on the conditions such as composition of the green compact, the pulverizing method of the fine powder raw materials, particle size, etc. For example, the sintering may be performed at 1000 C.1100 C. for 112 hours. In addition, in the case of using the eutectic alloys, such as 80% Nd-20% Co, 70Nd-30% Cu, 80% Nd-20% Ga calculated with atomic %, as the second, third, fourth alloys in the confecting process, the temperature during increasing the temperature in the sintering process is slowly increased to the temperature region of 500900 C., in which the melting point of each eutectic alloy falls, in the way that liquid phases produced from each easily eutectic alloy react with each other, and thus the formation of the RCoCu-M-Fe phases is promoted. Heating rate can be controlled with the consideration of the composition and the microstructure.

(50) The heat treating process is a process for subjecting the sintered body to an aging treatment. After this process, the width of the two-grain boundary parts formed between the adjacent R.sub.2T.sub.14B main phase crystal grains and the composition of the grain boundary phases formed in the two-grain boundary parts are determined. However, these microstructures are not controlled only in this process, but determined by considering both the conditions of the above sintering process and the situation of the fine powder raw materials. Hence, the temperature and time period for the heat treatment can be set under the consideration of the relationship between the conditions of the heat treatment and the microstructures of the sintered body. The heat treatment may be performed at a temperature of 500 C.900 C., and may also be performed in two stages comprising a heat treatment in the vicinity of 800 C. followed by a heat treatment in the vicinity of 550 C. The width of the two-grain boundary part can be controlled by setting the composition of the alloys raw materials, the sintering condition and the heat treating condition respectively. An example of heat treating process is described as the method of controlling the width of the two-grain boundary parts. The width of the two-grain boundary parts may also be controlled according to the compositional factor as recited in Table 1.

(51) In the present invention, each element, i.e., R, Co, Cu, M, Fe, used to form the RCoCu-M-Fe phases is introduced in the sintered body through the grain boundary diffusion method after the sintered body is produced. By applying the grain boundary diffusion method, Co, Cu, and M can be distributed with a high concentration in the grain boundary containing the triple junctions and the two-grain boundary parts, which is considered to be helpful to form the RCoCu-M-Fe phases. Specially, since the solid solution of Co is formed in the R.sub.2T.sub.14B main phase grains, the grain boundary diffusion method is used in which the grain boundary is taken as a channel to make elements diffuse in the sintered body, and thus solid solution in the main phase is inhibited, and the concentration of Co, Cu and Ga in the grain boundary can be enhanced.

(52) It is well known that the grain boundary diffusion method is the one in which the diffusion elements are prepared into vapor, or the powder of the solid diffusion materials are deposited onto the surface of the sintered body and then are subjected to a heat treatment. And any one of the methods mentioned above can be adopted. In the case of adopting the method of using vapor, the concentration of the vapor needs to be properly adjusted, while in the case of using the powder of the diffusion materials, the deposited amount of the diffusion powder needs to be properly adjusted. The condition of the heat treatment during diffusion is preferred to perform for about 1 to 24 hours at 5501000 C. In this temperature range, the triple junction or the grain boundary phases of the two-grain boundary parts become liquid phase and then the liquid phase will ooze to the surface of the sintered body through the grain boundary. Thus, the diffusion elements can be provided into the sintered body through the oozed liquid phase.

(53) R and Fe are rich in the sintered body, so only Co, Cu, and M can be subjected to the grain boundary diffusion. Co, Cu and M all have eutectic composition at the R-rich side, and thus their melting points are relatively low. The melted diffusion materials can effectively supply the diffusion elements to the liquid phases oozing from the sintered body. For example, the eutectic alloys of RCo, RCu and R-M have low melting point, and they can be used as the diffusion materials. In this case, the mixed powder of RCo, RCu and R-M can be used for diffusion. The heat treatment of the grain boundary diffusion can be performed to diffuse all essential elements at once, but it is preferable that the elements are diffused through different heat treatment according to the species of the element. The heat treatment during the introduction and after the introduction is very important for the formation of the two-grain boundary parts. As the same as mentioned above, the temperature and time period of the heat treatment can be set with the consideration of the relation between the conditions of the heat treatment and the microstructure of the sintered body.

(54) The R-T-B based sintered magnet according to the present embodiment can be obtained via the above methods. However, the producing method for the R-T-B based sintered magnet is not limited to the above methods and can be suitably modified.

(55) Next, the evaluation for the rate of demagnetization at high temperature of the R-T-B based sintered magnet according to this embodiment is described. The shape of the sample used for evaluation is not particularly limited. For example, in the present embodiment, a 10 mm10 mm4 mm of rectangular shaped R-T-B based sintered magnet can be used. The orientation direction of c axis of an R.sub.2T.sub.14B crystal grain is the direction perpendicular to a wide plane of 10 mm10 mm. Firstly, residual flux of the sample at a room temperature (25 C.) is measured after pulse magnetization with 5T, and then the value is taken as B0. The residual flux may be measured by for example a magnetic flux meter. Next, the sample is exposed to a high temperature of 130 C. for 2 hours, and back to the room temperature. Once the temperature of the sample returns to the room temperature, the residual flux is measured again and taken as B1. As such, the rate of demagnetization at high temperature D is evaluated by the formula below.
D=(B1B0)/B0*100(%)

(56) In this embodiment, observation is performed with a scanning transmission electron microscope (STEM), the position of the midpoint 2c of the two-grain boundary part is determined as shown in FIG. 2, and then the thickness of the two-grain boundary part is measured. Further, the content ratios of the elements in the midpoint 2c of the two-grain boundary part are calculated as the composition of the grain boundary phase exists in the two-grain boundary part by performing point analysis with the energy dispersive X-ray spectroscopy (STEM-EDS) attached in STEM.

(57) In the case that the obtained R-T-B based sintered magnet according to the present embodiment is used as a magnet for a rotary machine such as motor, the R-T-B based sintered magnet can be produced into a high reliable rotary machine with its output hardly reduced, such as motor, due that demagnetization at a high temperature hardly occur. The R-T-B based sintered magnet according to the present embodiment can be preferably used as a magnet of surface magnet type (Surface Permanent Magnet: SPM) motor wherein a magnet is attached on the surface of a rotor, an interior magnet embedded type (Interior Permanent Magnet: IPM) motor such as inner rotor type brushless motor, PRM (Permanent magnet Reluctance Motor) and the like. In concrete, the R-T-B based sintered magnet according to the present embodiment is preferably used for a spindle motor or a voice coil motor for a hard disk rotary drive of a hard disk drive, a motor for an electric vehicle or a hybrid car, an electric power steering motor for an automobile, a servo motor for a machine tool, a motor for vibrator of a cellular phone, a motor for a printer, a motor for a magnet generator and the like.

(58) <A Motor>

(59) Next, a preferable embodiment of the R-T-B based sintered magnet according to the present embodiment used as a motor will be described. Here, an example of the R-T-B based sintered magnet according to the present embodiment applied to SPM motor is described. FIG. 3 is a cross-sectional view briefly showing an embodiment of the structure of SPM motor. As shown in FIG. 3, SPM motor 10 comprises a columnar shaped rotor 12, a cylindrical shaped stator 13 and rotary shaft 14 in a housing 11. Rotary shaft 14 goes through a center of cross-section of rotor 12.

(60) Rotor 12 comprises a columnar shaped rotor core (iron core) 15 of iron material and the like, a plural number of permanent magnets 16 arranged at a predetermined interval on outer peripheral surface of rotor core 15 and a plural number of magnet insert slots 17 containing the permanent magnet 16. The R-T-B based sintered magnet according to the present embodiment is used for the permanent magnet 16. A plural number of the permanent magnets 16 are set so as to arrange N-pole and S-pole alternately in each magnet insert slot 17 along a circumferential direction of the rotor 12. Thus, adjacent permanent magnets 16 generate magnetic field lines in mutually reversed directions along radial direction of rotor 12.

(61) Stator 13 comprises a plural number of stator cores 18 and throttles 19, arranged at a predetermined interval along a circumferential direction of inner side of its cylindrical wall (peripheral wall) and along outer peripheral surface of rotor 12. Said plural number of stator cores 18 are arranged so as to be directed toward stator 13 and opposed to rotor 12. Further, coil 20 is wound around inside the each throttle 19. A permanent magnet 16 and stator core 18 are set so as to be opposed mutually.

(62) Rotor 12, together with rotary shaft 14, is turnably installed in a space in stator 13. Stator 13 provides torque to rotor 12 by an electromagnetic action, and rotor 12 rotates along circumferential direction.

(63) SPM motor 10 uses the R-T-B based sintered magnet according to the present embodiment as a permanent magnet 16. The permanent magnet 16 shows high magnetic characteristics and is hardly subjected to demagnetization at a high temperature. SPM motor 10 is thus capable of improving motor characteristics, such as a torque characteristic, and showing a high output for a long term; and that said SPM motor 10 is excellent in reliability.

(64) Next, the present invention will be described in more detail based on specific examples. However, this invention is not limited to the following examples.

EXAMPLES

(65) (Preparation of Sintered Bodies)

(66) The sintered bodies used in Examples 17 and Comparative Examples 12 were produced by two alloys method. Firstly, raw material alloys were manufactured by a strip casting method to obtain an R-T-B based sintered magnet having a magnet composition I or a magnet composition II as shown in Table 1 and Table 2. As for raw material alloys, four kinds of alloys, i.e., the first alloys A and B mainly to form main phases of a magnet, the second alloys a and b mainly to form grain boundary parts, were prepared. In addition, in Table 1 and Table 2 (also applicable to Table 3), bal. referred to the remaining amount when the total composition was deemed as 100 mass % in each alloy, and (T.RE) represented the sum of the rare earth based elements (mass %).

(67) TABLE-US-00001 TABLE 1 Composition (mass %) Nd Pr (T. RE) Co Ga Al Cu B Fe Mass ratio First alloy A 23.5 6.5 30.0 0.0 0.0 0.2 0.0 1.0 bal. 95 Second alloy a 39.0 11.0 50.0 0.0 0.0 0.2 0.0 0.0 bal. 5 Magnet composition I 24.3 6.7 31.0 0.0 0.0 0.2 0.0 0.9 bal.

(68) TABLE-US-00002 TABLE 2 Composition (mass %) Mass Nd Pr (T. RE) Co Ga Al Cu B Fe ratio First alloy B 23.5 6.5 30.0 0.0 0.0 0.2 0.0 1.0 bal. 95 Second alloy b 39.0 11.0 50.0 10.0 8.0 0.2 14.0 0.0 bal. 5 Magnet composition II 24.3 6.7 31.0 0.50 0.4 0.2 0.7 0.9 bal.

(69) Next, after hydrogen was stored to each of the alloys at room temperature, a hydrogen storage pulverization (coarse pulverization) for desorbing hydrogen was performed in Ar atmosphere at 600 C. for 1 hour.

(70) In addition, in the present example, each step, from the hydrogen storage pulverization to the sintering process, (the fine pulverization and pressing process) was done in an Ar atmosphere with the oxygen concentration therein being lower than 50 ppm (same conditions were applied in the following examples and comparative examples).

(71) Next, for each alloy, after the hydrogen storage pulverization and before the fine pulverization, 0.1 mass % of zinc stearate was added to the coarsely pulverized powder as a pulverization aid. Then, the mixture was mixed by a Nauta mixer. And then, a jet mill was used to perform the fine pulverization so as to provide a fine powder raw material having an average particle size of around 4.0 m.

(72) Subsequently, the obtained fine powder raw material of the first alloy and that of the second alloy were mixed in a mass ratio of 95:5 by using the Nauta mixer so that a mixed powder of the starting powder of the R-T-B based sintered magnet was prepared.

(73) The obtained mixed powder was filled in a press mold arranged in an electromagnet, and the powder was pressed under an applied pressure of 120 MPa in a magnetic field of 1200 kA/m. In this way, the green compact was obtained.

(74) Next, the temperature rose in a rate of 10 C./min under vacuum, and then the green compact was sintered at 1060 C. for 4 hours and then rapidly cooled to provide a sintered body (the R-T-B based sintered magnet) having the composition I or II as shown in Table 1. Next, machining was conducted by using a vertical processing machine to provide a rectangular solid with a shape of 10.1 mm10.1 mm4.2 mm. The orientation direction of c axis of the R.sub.2T.sub.14B crystal grain was the direction of 4.2 mm thickness.

(75) (Preparation of Powder of Diffusion Materials)

(76) The diffusion materials were produced in order to introduce the elements i.e., Co, Cu, and M, into the sintered body by a grain boundary diffusion method using powder of the diffusion materials. The metals were weighted with a ratio of being the composition of the diffusion materials 18 as shown in Table 3, and then melt and casted by an arc melting furnace. This operation was repeated three times to prepare an alloy. The obtained alloy was melt by high frequency induction heating, and then the molten metal was rapidly cooled by a roll to produce a quenched ribbon. The obtained quenched ribbon was coarsely pulverized in a glove box with Ar substituted, and then was put into a well-closed container together with a stainless pulverization medium. The coarsely pulverized powder was pulverized in the well-closed container to obtain a powder with an average particle size of 1020 m. In addition, the obtained powder of the diffusion materials was got in the glove box, and then subjected to a slow oxidation treatment with a safe operation in the air. A binder resin was added into the thus obtained powder of the diffusion materials to produce a coating of the diffusion materials with an alcohol as the solvent. As for the mixing ratio, in the case of taking the mass of the powder of diffusion materials as 100, the amount of the fine powder of the butyral used as the binder resin was 2, and the amount of the alcohol was 100. The mixture was added into a resin cylinder-typed container having a lid. The container was closed, and then put on the stand of a ball mill. The mixture was subject to rotation in a rate of 120 rpm to produce into a coating.

(77) TABLE-US-00003 TABLE 3 Composition (atomic %) Coating amount Nd Co Cu Ga Si Sn Ge Bi wt %/time Diffusion material 1 80.0 20.0 0.0 0.0 0.0 0.0 0.0 0.0 5.5 Diffusion material 2 70.0 0.0 30.0 0.0 0.0 0.0 0.0 0.0 4.5 Diffusion material 3 80.0 0.0 0.0 20.0 0.0 0.0 0.0 0.0 3.8 Diffusion material 4 87.5 0.0 0.0 0.0 12.5 0.0 0.0 0.0 6.2 Diffusion material 5 88.0 0.0 0.0 0.0 0.0 12.0 0.0 0.0 6.9 Diffusion material 6 90.0 0.0 0.0 0.0 0.0 0.0 10.0 0.0 8.0 Diffusion material 7 92.2 0.0 0.0 0.0 0.0 0.0 0.0 7.8 11.3 Diffusion material 8 80.0 6.7 8.7 4.5 0.0 0.0 0.0 0.0 5.5

Comparative Example 1

(78) The machined article of the sintered body with the magnet composition I was subjected to an aging treatment at 900 C. for 18 hours and then at 540 C. for 2 hours (both in Ar atmosphere), and taken as Comparative Example 1.

Comparative Example 2

(79) The machined article of the sintered body with the magnet composition I (with a shape of 10.1 mm10.1 mm4.2 mm) was coated by the diffusion material 8 of Table 3, wherein two wide surfaces of 10.1 mm10.1 mm of the machined article were evenly coated with using 5.5 wt % of the diffusion material in total. Then, a diffusion heat treatment was performed at 900 C. for 6 hours in the Ar atmosphere, and the residual diffusion material on the coated surfaces was removed with sandpaper. Again, the machined article was coated by the same amount of diffusion material 8, a diffusion heat treatment was performed at 900 C. for 6 hours in the Ar atmosphere, and the residual diffusion material on the coated surfaces was removed in the same way. Further, the machined article was coated by the same amount of diffusion material 8, and then a diffusion heat treatment was performed at 900 C. for 6 hours. In short, the steps of coating the machined article with 5.5 wt % of the diffusion material 8 and performing the heat treatment at 900 C. for 6 hours in the Ar atmosphere was repeated three times. Subsequently, the aging treatment was performed at 540 C. for 2 hours in the Ar atmosphere. The residual diffusion material on the coated surfaces were removed with sandpaper, and thus an R-T-B based sintered magnet was obtained.

Examples 1 to 5

(80) The machined articles of the sintered body with the magnet composition I (with a shape of 10.1 mm10.1 mm4.2 mm) were respectively coated by the diffusion materials 37 of Table 3, wherein two wide surfaces of 10.1 mm10.1 mm of the machined articles were evenly coated with the amount of diffusion material as respectively shown in Table 3. Then, a diffusion heat treatment was performed at 900 C. for 6 hours in the Ar atmosphere. After the heat treatment, the residual diffusion material on the coated surfaces were removed with sandpaper. Next, the two surfaces of the machined articles were coated by the diffusion material 2 of 4.5 wt % in total, and then the heat treatment was performed at 900 C. for 6 hours in the Ar atmosphere in the same way. After the heat treatment, the residual diffusion material on the coated surfaces were removed with sandpaper. Then, the two surfaces of the machined article were coated by 5.5 wt % of the diffusion material 1 in total, and the heat treatment was performed at 900 C. for 6 hours in the Ar atmosphere in the same way. Next, the aging treatment was carried out at 540 C. for 2 hours in the Ar atmosphere. The residual diffusion material on the coated surfaces were removed with sandpaper to obtain each R-T-B based sintered magnet. The different diffusion materials were used in the initial diffusion heat treatment, and the R-T-B based sintered magnet obtained by using the diffusion materials 3, 4, 5, 6, 7 were regarded as Examples 1, 2, 3, 4, 5, respectively.

Example 6

(81) The machined article of the sintered body with the magnet composition I (with a shape of 10.1 mm10.1 mm4.2 mm) was coated by the diffusion material 3 of Table 3, wherein two wide surfaces of 10.1 mm10.1 mm of the machined article were evenly coated with using 3.8 wt % of the diffusion material in total. Then, a diffusion heat treatment was performed at 800 C. for 10 hours in the Ar atmosphere. After the heat treatment, the residual diffusion material on the coated surfaces were removed with sandpaper. Next, the two surfaces of the machined article were coated by 4.5 wt % of the diffusion material 2 in total, and then the heat treatment was performed at 800 C. for 10 hours in the Ar atmosphere in the same way. After the heat treatment, the residual diffusion material on the coated surfaces were removed with sandpaper. The two surfaces of the machined article were coated by 5.5 wt % of the diffusion material 1 in total, and then the heat treatment was performed at 800 C. for 10 hours in the Ar atmosphere in the same way. Next, the aging treatment was carried out at 540 C. for 2 hours in the Ar atmosphere. The residual diffusion material on the coated surfaces were removed with sandpaper to obtain the R-T-B based sintered magnet.

Example 7

(82) The machined article of the sintered body with the magnet composition I (with a shape of 10.1 mm10.1 mm4.2 mm) was coated by the diffusion material 1 of Table 3, wherein two wide surfaces of 10.1 mm10.1 mm of the machined article were evenly coated with using 5.5 wt % of the diffusion material in total. Then, a diffusion heat treatment was performed at 900 C. for 6 hours in the Ar atmosphere. After the heat treatment, the residual diffusion material on the coated surfaces were removed with sandpaper. Next, the two surfaces of the machined article were coated by 4.5 wt % of the diffusion material 2 in total, and then the heat treatment was performed at 900 C. for 6 hours in the Ar atmosphere in the same way. After the heat treatment, the residual diffusion material on the coating surfaces were removed with sandpaper. The two surfaces of the machined article were coated by 5.4 wt % of the diffusion material 3 in total, and then the heat treatment was performed at 900 C. for 10 hours in the Ar atmosphere in the same way. Next, the aging treatment was carried out at 540 C. for 2 hours in the Ar atmosphere. The residual diffusion material on the diffusion material coating surfaces were removed with sandpaper to obtain the R-T-B based sintered magnet.

(83) In the obtained comparative examples and examples, coating the diffusion material, heat treatment and the surface machining with the sandpaper was repeated, so in order to ensure smoothness and parallelism of the surfaces, grinding was performed in Comparative Examples 1 to 2 and Examples 1 to 7, and all the R-T-B based sintered magnets in Comparative Examples 1 to 2 and Examples 1 to 7 were produced into a rectangular solid with a shape of 10.0 mm10.0 mm4.0 mm.

(84) The results of the composition analysis by means of X-ray fluorescence analysis and ICP were shown in Table 4. The compositions in Comparative Examples 1 to 2 and Examples 1, 6, 7 were almost the same one. Further, in Examples 1 to 5, the kinds of contained M (Ga, Si, Sn, Ge, Bi) and its amount were different, while the other compositions were the same.

(85) It could be found out in the samples using the grain boundary diffusion method that the amounts of Co, Cu, and M were increased, and the increased amount of Nd was little although it occupies seven or more out of ten in the composition of the each diffusion materials based on the atomic ratio. The reason was considered that the concentration of Nd in the grain boundary comprising the grain boundary triple junction and the two-grain boundary part contained in the sintered body was high, and thus the sufficient concentration gradient could not be achieved to diffuse into the sintered body. That is, it could be known that the properties were not improved by increasing the amount of R in the present invention.

(86) TABLE-US-00004 TABLE 4 Species of Diffusion time Diffusion Magnet diffusion material period (hr) temperature composition First Second Third First Second Third ( C.) Comparative II 900 Example 1 Comparative I 8 8 8 6 6 6 900 Example 2 Example 1 I 3 2 1 6 6 6 900 Example 2 I 4 2 1 6 6 6 900 Example 3 I 5 2 1 6 6 6 900 Example 4 I 6 2 1 6 6 6 900 Example 5 I 7 2 1 6 6 6 900 Example 6 I 3 2 1 10 10 10 800 Example 7 I 1 2 3 6 6 6 900 Composition (mass %) Nd Pr (T. RE) Co Cu Ga Si Sn Ge Bi Al B Fe Comparative 24.3 6.7 31.0 0.5 0.7 0.4 0.0 0.0 0.0 0.0 0.2 0.9 bal. Example 1 Comparative 24.3 6.7 31.0 0.5 0.7 0.4 0.0 0.0 0.0 0.0 0.2 0.9 bal. Example 2 Example 1 24.7 6.7 31.4 0.5 0.7 0.4 0.0 0.0 0.0 0.0 0.2 0.9 bal. Example 2 24.8 6.7 31.5 0.4 0.7 0.0 0.2 0.0 0.0 0.0 0.2 0.9 bal. Example 3 24.7 6.7 31.4 0.4 0.7 0.0 0.0 0.7 0.0 0.0 0.2 0.9 bal. Example 4 24.7 6.7 31.4 0.5 0.7 0.0 0.0 0.0 0.4 0.0 0.2 0.9 bal. Example 5 24.8 6.7 31.5 0.5 0.7 0.0 0.0 0.0 0.0 0.8 0.2 0.9 bal. Example 6 24.8 6.7 31.5 0.5 0.7 0.4 0.0 0.0 0.0 0.0 0.2 0.9 bal. Example 7 24.7 6.7 31.4 0.5 0.7 0.4 0.0 0.0 0.0 0.0 0.2 0.9 bal.

(87) The composition analysis at the point 2c on the grain boundary of each sample was measured and the thickness of the two-grain boundary part was measured by the means of TEM-EDS with the same method as mentioned above. The results obtained by classifying the grain boundary phase exist in the two-grain boundary part according to the values of composition analysis were shown in Table 5, together with the results of the residual magnetic flux density Br, the coercivity Hcj and demagnetization rate at a high temperature. In Comparative Examples 1 and 2, the RCoCu-M-Fe phase did not exist while the number of the RCu-M-Fe phase was high. On the other hand, in Examples 1 to 5, the RCoCu-M-Fe phase existed, and the relation of the number (A) of the RCoCu-M-Fe phase and that (B) of the RCu-M-Fe phase became A>B. As for the number (C) of the R.sub.6F.sub.13M phase and the number (D) of the R phase, no significant difference was found in Comparative Examples and Examples. The Hcj and the demagnetization rate at a high temperature were highly improved in Examples 1 to 5 in which RCoCu-M-Fe phases existed, and further the decrease of Br was inhibited.

(88) In Example 6, the same diffusion materials were used in the same order as those in Example 1, but due to the difference of the time period in the heat treatment, the number (A) of the RCoCu-M-Fe phase and the number (B) of the RCu-M-Fe phase changed. Though A in Example 6 was equal to or higher than that in Examples 1 to 5, B in Example 6 was 0. And as for the magnetic properties, Hcj and demagnetization rate at a high temperature had little change, while Br reduced.

(89) In Example 7, the diffusion material with the same composition as that in Example 1 was used. However, the number (A) of the RCoCu-M-Fe phase and the number (B) of the RCu-M-Fe phase changed based on the difference of the use order. A is more than B in Examples 1 to 5 while A is less than B in Example 7. The magnetic properties for Example 7 were improved in comparison with those of Comparative Examples. However, Hcj and demagnetization rate at a high temperature were inferior to those for Examples 1 to 5.

(90) TABLE-US-00005 TABLE 5 Demagnetization Formation number of two-grain boundary part of each phase rate at a high RCoCuMFe RCuMFe R.sub.6T.sub.13M R Other Br Hcj temperature A B C D E mT kA/m % Comparative 0 11 5 4 0 1380 1329 18.0 Example 1 Comparative 0 10 4 6 0 1378 1334 16.8 Example 2 Example 1 12 2 4 2 0 1370 1672 0.2 Example 2 10 4 3 3 0 1372 1666 0.4 Example 3 8 6 3 3 0 1369 1670 0.2 Example 4 14 2 2 2 0 1365 1665 0.3 Example 5 9 6 4 1 0 1370 1650 0.8 Example 6 13 0 3 4 0 1345 1675 0.1 Example 7 4 10 2 2 0 1375 1520 5.5

(91) The measurement results of the thickness of the two-grain boundary part were shown in Table 6. The thickness of the two-grain boundary parts formed by RCoCu-M-Fe phases fell into the range of 5 to 500 nm, and thus the thickness was very thick. On the other hand, the thickness of the two-grain boundary parts formed by RCu-M-Fe phases was as thin as 2 to 15 nm, and thus it could be considered the decrease of the volume ratio of the main phases could be inhibited. The thick two-grain boundary part could be formed by R.sub.6T.sub.13M phases or R phases, but it could be seen from Table 5 that the number was low. Thus, it could be thought of that the formation of two-grain boundary parts by RCoCu-M-Fe phases made a contribution to the improvement of demagnetization rate at a high temperature.

(92) TABLE-US-00006 TABLE 6 RCoCuMFe RCuMFe R.sub.6T.sub.13M R nm nm nm nm Comparative Example 1 Average 7 180 22 Maximum 15 250 31 Minimum 4 110 12 Comparative Example 2 Average 8 212 41 Maximum 12 370 125 Minimum 3 30 8 Example 1 Average 225 9 143 155 Maximum 498 12 200 235 Minimum 25 6 66 120 Example 2 Average 148 6 98 152 Maximum 198 13 188 288 Minimum 25 3 60 15 Example 3 Average 231 4 167 176 Maximum 433 6 183 199 Minimum 19 2 113 153 Example 4 Average 98 7 131 84 Maximum 225 11 229 155 Minimum 32 3 32 12 Example 5 Average 215 7 158 98 Maximum 320 8 430 98 Minimum 5 5 8 98 Example 6 Average 215 6 187 146 Maximum 320 8 253 203 Minimum 22 5 12 11 Example 7 Average 111 9 271 99 Maximum 155 10 300 187 Minimum 40 7 55 34

(93) The compositions of the RCoCu-M-Fe phase confirmed in Example 1 were shown in Table 7. The content of Fe was all 35.7 atomic % or less, and it was very low. It could be considered that magnetization significantly reduced compared to that of the well-known grain boundary phase in the prior art. Moreover, that the concentration of Cu was very high was also a feature. M was Ga in Example 1. In Examples 2 to 7 using the other M, the compositions of RCoCu-M-Fe phase were the same, and they could be classified by the above classification method.

(94) TABLE-US-00007 TABLE 7 Analysis Composition of RCoCuGaFe phase (atomic %) point Pr Nd Cu Ga Fe Co 1 15.3 46.0 15.3 8.5 7.2 7.7 2 17.6 48.7 21.0 3.3 2.7 6.7 3 9.4 32.8 47.3 5.5 2.5 2.5 4 17.3 49.3 17.8 3.8 4.9 7.0 5 15.0 43.6 15.9 2.6 18.1 4.9 6 13.7 39.7 13.5 2.4 24.8 5.9 7 9.3 36.8 40.7 5.5 4.8 2.9 8 12.8 32.2 12.5 2.5 35.6 4.4 9 17.3 47.5 7.8 2.1 22.1 3.2 10 16.8 47.5 19.8 3.6 7.2 5.1 11 18.8 38.4 12.6 11.3 10.9 8.0 12 9.6 34.7 39.2 5.1 8.7 2.7

(95) The demagnetization rate at a high temperature was attempted to improve by the steps different from those in Examples 8 to 11. The raw material alloys were prepared to produce the sintered body having the magnet composition III to VI in Table 8 to 11. The compositions of Examples 8, 9, 10, 11 were magnet compositions III, IV, V, VI, respectively. Each the first alloy of Tables 8 to 11 was produced by the strip casting method. On the other hand, the compositions of the second, third and fourth alloys were the same as those of diffusion materials 1, 2 and 3. The quenched ribbon was produced by rapidly cooling by the similar manufacturing method of diffusion materials, and then pulverized into 40 m. After 0.1 wt % of zinc stearate was added without a slow oxidation treatment, a jet mill was used to perform the fine pulverization so as to provide a fine powder raw material having an average particle size of 4.0 m. Subsequently, the fine powder raw materials of the first to fourth alloys were produced into a mixed powder with a ratio as shown in the table by using the Nauta mixer. The obtained mixed powder was filled in a press mold arranged in an electromagnet, and the powder was pressed under an applied pressure of 120 MPa in a magnetic field of 1200 kA/m. In this way, the green compact was obtained. The green compact was sintered under vacuum. At this time, the temperature range of 500900 C. in the heating part of the sintering temperature pattern was raised in a rate of 0.5 C./min, the temperature range except the above was raised in a rate of 10 C./min until the temperature reached at 1060 C. The temperature was kept at 1060 C. for 4 hours to perform the sintering step, and then the sintered body was rapidly cooled, subjected to an aging treatment at 900 C. for 18 hours and then at 540 C. for 2 hours (both in Ar atmosphere). The obtained R-T-B based sintered magnet was machined to produce into a rectangular solid with a shape of 10.0 mm10.0 mm4.0 mm. The orientation direction of c axis in the R.sub.2T.sub.14B crystal grain was the thickness one of 4.0 mm.

(96) TABLE-US-00008 TABLE 8 Composition (mass %) Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe raito First alloy 21.46 5.94 0.00 27.40 1.40 0.00 0.03 0.00 1.60 1.01 bal. 94 Second alloy 90.73 0.00 0.00 90.73 9.27 0.00 0.00 0.00 0.00 0.00 0.00 2 Third alloy 84.12 0.00 0.00 84.12 0.00 0.0 0.00 15.88 0.00 0.00 0.00 2 Fourth alloy 89.22 0.00 0.00 89.22 0.00 10.78 0.00 0.00 0.00 0.00 0.00 2 Magnet composition III 25.46 5.58 0.00 31.04 1.50 0.22 0.03 0.32 1.50 0.95 bal.

(97) TABLE-US-00009 TABLE 9 Composition (mass %) Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe ratio First alloy 21.15 5.85 0.00 27.00 3.13 0.63 0.11 0.95 0.00 0.83 bal. 90 Second alloy 90.73 0.00 0.00 90.73 9.27 0.00 0.00 0.00 0.00 0.00 0.00 2 Third alloy 84.12 0.00 0.00 84.12 0.00 0.0 0.00 15.88 0.00 0.00 0.00 4 Fourth alloy 89.22 0.00 0.00 89.22 0.00 10.78 0.00 0.00 0.00 0.00 0.00 4 Magnet composition IV 27.78 5.26 0.00 33.05 3.00 1.00 0.10 1.49 0.00 0.75 bal.

(98) TABLE-US-00010 TABLE 10 Composition (mass %) Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe ratio First alloy 20.99 5.81 0.20 27.00 0.00 0.00 0.63 0.00 0.11 0.97 bal. 95 Second alloy 90.73 0.00 0.00 90.73 9.27 0.00 0.00 0.00 0.00 0.00 0.00 3 Third alloy 84.12 0.00 0.00 84.12 0.00 0.0 0.00 15.88 0.00 0.00 0.00 1 Fourth alloy 89.22 0.00 0.00 89.22 0.00 10.78 0.00 0.00 0.00 0.00 0.00 1 Magnet composition V 24.40 5.52 0.19 30.11 0.28 0.11 0.60 0.16 0.10 0.92 bal.

(99) TABLE-US-00011 TABLE 11 Composition (mass %) Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe ratio First alloy 21.31 5.89 0.00 27.20 0.70 0.50 0.25 0.00 0.42 0.91 bal. 92 Second alloy 90.73 0.00 0.00 90.73 9.27 0.00 0.00 0.00 0.00 0.00 0.00 4 Third alloy 84.12 0.00 0.00 84.12 0.00 0.0 0.00 15.88 0.00 0.00 0.00 2 Fourth alloy 89.22 0.00 0.00 89.22 0.00 10.78 0.00 0.00 0.00 0.00 0.00 2 Magnet composition VI 26.70 5.42 0.00 32.12 1.01 0.68 0.23 0.32 0.39 0.84 bal.

(100) In Comparative Examples 3 to 6, the sintered bodies with the same magnet compositions IIIVI as those in Examples 8 to 11 were prepared. The first and the second alloys produced by the strip casting method were used as the raw material alloy of these comparative examples. The compositions in Comparative Examples 3, 4, 5, and 6 were respectively magnet compositions III, IV, V, and VI in this order. The alloy composition used to produce each sintered body with the magnet composition of Comparative Examples 3 to 6 was shown in Tables 1215. The production process in Comparative Examples 3 to 6 was the same as that in Comparative Example 1. The obtained R-T-B based sintered magnet was subjected to grinding to provide a rectangular solid with a shape of 10.0 mm10.0 mm4.0 mm. The orientation direction of c axis in the R.sub.2T.sub.14B crystal grain was the thickness one of 4.0 mm.

(101) TABLE-US-00012 TABLE 12 Composition mass % Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe ratio Fist alloy 24.74 5.30 0.00 30.04 0.00 0.00 0.03 0.00 1.58 1.00 bal. 95 Second alloy 39.00 11.00 0.00 50.00 30.03 4.31 0.00 6.35 0.00 0.00 bal. 5 Magnet composition III 25.46 5.58 0.00 31.04 1.50 0.22 0.03 0.32 1.50 0.95 bal.

(102) TABLE-US-00013 TABLE 13 Composition (mass %) Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe ratio Fist alloy 27.19 4.96 0.00 31.17 1.50 0.00 0.11 0.00 0.00 0.83 bal. 90 Second alloy 39.00 11.00 0.00 50.00 16.50 10.00 0.00 14.90 0.00 0.00 bal. 10 Magnet composition IV 27.78 5.26 0.00 33.05 3.00 1.00 0.10 1.49 0.00 0.75 bal.

(103) TABLE-US-00014 TABLE 14 Composition (mass %) Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe ratio Fist alloy 23.63 5.23 0.20 29.06 0.00 0.00 0.63 0.00 0.11 0.97 bal. 95 Second alloy 39.00 11.00 0.00 50.00 5.56 2.16 0.00 3.18 0.00 0.00 bal. 5 Magnet composition V 24.40 5.52 0.19 30.11 0.28 0.11 0.60 0.16 0.10 0.92 bal.

(104) TABLE-US-00015 TABLE 15 Composition (mass %) Mass Nd Pr Dy (T. RE) Co Ga Al Cu Zr B Fe ratio Fist alloy 26.05 5.13 0.00 31.18 0.00 0.00 0.24 0.00 0.41 0.88 bal. 95 Second alloy 39.00 11.00 0.00 50.00 20.30 13.51 0.00 6.35 0.00 0.00 bal. 5 Magnet composition VI 26.70 5.42 0.00 32.12 1.01 0.68 0.23 0.32 0.39 0.84 bal.

(105) As for Examples 811 and Comparative Examples 36, the composition at the point 2c in the two-grain boundary part of each sample was analyzed and the thickness of the two-grain boundary part was measured by the means of TEM-EDS. The results obtained by classifying the grain boundary phase exist in the two-grain boundary part according to the values of composition analysis were shown in Table 16, together with the results of the residual magnetic flux density Br, the coercivity Hcj and demagnetization rate at a high temperature. In each comparative example, no RCoCu-M-Fe phase had been found while the RCu-M-Fe phase was formed in each example. In the examples and comparative examples, if compared among the ones with the same magnet composition, demagnetization rate at a high temperature was improved in examples. The formation process of RCoCu-M-Fe phase was not clear. It could be considered that since the second alloy had a liquid phase forming temperature of 625 C., the third alloy had a liquid phase forming temperature of 520 C., and the fourth alloy had a liquid phase forming temperature of 651 C., liquid phases of the second, third and fourth alloys easily reacted with each other as raising temperature to the range of 500900 C. with a rate of 0.5 C./min, which could help to form RCoCu-M-Fe phases.

(106) TABLE-US-00016 TABLE 16 Formation number of two-grain boundary part of Demagnetization each phase rate at high Magnet RCoCuMFe RCuMFe R.sub.6T.sub.13M R Other Br Hcj temperature composition A B C D E mT kA/m % Example 8 III 10 2 3 5 0 1326 1479 8.0 Example 9 IV 9 1 5 5 0 1286 1750 2.1 Example 10 V 6 10 2 2 0 1408 1271 19.1 Example 11 VI 11 3 2 4 0 1347 1739 1.9 Comparative III 0 4 12 4 0 1336 1318 17.2 Example 3 Comparative IV 0 1 13 6 0 1317 1437 10.0 Example 4 Comparative V 0 5 10 5 0 1410 1190 24.6 Example 5 Comparative VI 0 2 11 7 0 1360 1585 3.5 Example 6

(107) The measurement results of the thickness of the two-grain boundary part were shown in Table 17. Like Examples 17, it could be confirmed that the two-grain boundary parts formed by RCoCu-M-Fe phases were thick as 8444 nm.

(108) TABLE-US-00017 TABLE 17 RCoCuMFe RCuMFe R.sub.6T.sub.13M R nm nm nm nm Example 8 Average 230 9 223 20 Maximum 444 12 404 31 Minimum 27 6 30 12 Example 9 Average 144 7 247 51 Maximum 270 10 436 125 Minimum 22 6 46 8 Example 10 Average 122 7 182 178 Maximum 208 8 284 235 Minimum 36 6 79 120 Example 11 Average 115 7 118 200 Maximum 225 6 194 288 Minimum 8 7 42 116 Comparative Example 3 Average 11 132 171 Maximum 13 222 199 Minimum 6 48 153 Comparative Example 4 Average 9 231 133 Maximum 13 373 254 Minimum 6 80 24 Comparative Example 5 Average 9 181 111 Maximum 10 274 191 Minimum 7 82 28 Comparative Example 6 Average 7 189 124 Maximum 7 349 203 Minimum 6 92 31

(109) In addition, the compositions of RCoCu-M-Fe phase confirmed in Examples 811 at three points per one sample were shown in Table 18. The content of Fe had been confirmed to be very low and it was 27.4 atomic % or less, while the concentration of Cu had been found out to be very high. Thus, the same results as those in Table 7 were obtained.

(110) TABLE-US-00018 TABLE 18 Compostion of RCoCuGaFe Analysis phase (atomic %) point Pr Nd Dy Cu Ga Fe Co Example 8 1 14.2 33.2 0.0 35.0 9.3 6.0 2.3 2 16.0 41.2 0.0 22.3 2.9 10.1 7.5 3 12.3 31.6 0.0 17.7 8.5 20.6 9.3 Example 9 1 9.7 39.0 0.0 21.4 8.6 11.5 9.8 2 14.3 45.1 0.0 24.7 3.3 7.8 4.8 3 14.8 34.4 0.0 11.4 9.3 23.8 6.3 Example 10 1 9.0 26.8 0.1 29.8 9.6 16.5 8.3 2 11.8 31.6 0.5 12.6 10.5 27.4 5.6 3 9.9 31.7 0.1 34.7 3.5 15.2 4.9 Example 11 1 13.8 41.3 0.0 8.7 4.3 23.6 8.4 2 10.7 35.4 0.0 31.2 1.1 13.3 8.0 3 11.4 27.8 0.0 46.9 1.7 9.7 2.5

(111) It could be known from the above that the two-grain boundary parts formed by RCoCu-M-Fe phase existed in the R-T-B based sintered magnet of examples. The thickness of the two-grain boundary parts formed by RCoCu-M-Fe phase was 5500 nm. The coercivity had been increased and the demagnetization rate at a high temperature had been improved in examples. Further, the two-grain boundary parts formed by RCu-M-Fe phase also existed and was thin, and it would not decrease the volume ratio of the main phase, so it had the effect of inhibiting the decrease of the residual magnetic flux density. By obtaining the balance between the amount of two-grain boundary parts formed by RCu-M-Fe phase and that of two-grain boundary parts formed by RCoCu-M-Fe phase, both a high residual magnetic flux density and a good demagnetization rate at high temperature could be achieved.

(112) Hereinabove, the present invention is described based on the embodiments. The embodiments are illustrative, which can be subjected to various variation and modification within the scope of the claims of this invention as for those skilled in the art. Thus, the description of the present specification and the drawings should be deemed as illustrative but not limiting.

(113) According to the present invention, an R-T-B based sintered magnet that may be used even at a high temperature environment can be provided.

DESCRIPTION OF REFERENCE NUMERALS

(114) 1 main phase crystal grains 2 two-grain boundary part 2a, 2b boundary 2c the midpoint of the two-grain boundary phase 3 a triple junction 100 an R-T-B based sintered magnet 10 a SPM motor 11 a casing 12 a rotor 13 a stator 14 a rotating axis 15 a rotor core (iron core) 16 a permanent magnet 17 a magnet inserting slot 18 a stator core 19 a throttle 20 a coil