JP5012942B2 - Rare earth sintered magnet, manufacturing method thereof, and rotating machine - Google Patents

Description

  The present invention relates to a rare earth sintered magnet, a manufacturing method thereof, and a rotating machine including the rare earth sintered magnet.

  Rare earth sintered magnets mainly composed of R-Fe-B alloys having rare earth elements as constituent elements have good magnetic properties and are used in various fields as permanent magnets. Such a rare earth sintered magnet has the property of being easily oxidized because it contains a rare earth element.

  Therefore, in order to suppress corrosion due to oxidation of the rare earth sintered magnet, an attempt has been made to improve the corrosion resistance by providing a coating layer on the surface. For example, in Patent Document 1 below, it is proposed to improve corrosion resistance by laminating layers made of various metals on the surface of a rare earth sintered magnet.

JP 2001-196215 A

  However, according to the study by the present inventors, particularly when used under severe conditions under high temperature and high humidity, a coating layer is formed by laminating layers made of metal or alloy as in Patent Document 1 described above. Even so, it has been found that it is difficult to sufficiently suppress corrosion due to oxidation.

  This invention is made | formed in view of the said situation, and it aims at providing the rare earth sintered magnet excellent in corrosion resistance. Moreover, it aims at providing the rotary machine which can maintain the performance which was excellent over a long period of time by providing the rare earth sintered magnet excellent in corrosion resistance as mentioned above.

  The present invention includes a magnet body including an R-T-B alloy, and a coating layer on the magnet body, the coating layer including a first phase and a first phase. A second phase dispersed in a filler form, wherein the first phase includes an R-based alloy different from the R-T-B based alloy, and the second phase includes an R-Cu based alloy. A rare earth sintered magnet having a higher Cu content than the first phase is provided. Here, R represents a rare earth element, T represents a transition element, B represents a boron element, and Cu represents a copper element.

  The rare earth sintered magnet of the present invention has a coating layer including two phases having different Cu (copper element) contents on a magnet body including an R-T-B alloy. Among these phases, the first phase containing an R-based alloy and having a low Cu content is excellent in adhesion to the magnet body, and thus contributes to improvement in adhesion between the coating layer and the magnet body. . On the other hand, the second phase containing an R—Cu-based alloy and having a higher Cu content than the first phase has an action of suppressing the entry of hydrogen atoms and the like that cause corrosion of the rare earth sintered magnet. In addition, since such a second phase is dispersed in the first phase in the form of a filler, it is possible to lengthen the diffusion path of hydrogen atoms and other substances that cause corrosion. Since the coating layer having such characteristics is provided on the surface of the magnet body, the rare earth sintered magnet of the present invention has excellent corrosion resistance.

  In the rare earth sintered magnet of the present invention, the volume ratio of the second phase to the first phase is preferably 20 to 80% by volume. By containing the first phase and the second phase in such a volume ratio, it becomes possible to achieve both higher adhesion and corrosion resistance between the magnet body and the coating layer.

  In the rare earth sintered magnet of the present invention, the difference between the Cu content in the first phase and the Cu content in the second phase is preferably 30 to 60 atomic%. By having such a coating layer, diffusion of hydrogen atoms and the like in the coating layer is further suppressed, and a rare earth sintered magnet having further excellent corrosion resistance can be obtained.

  The present invention is also a method of manufacturing a rare earth sintered magnet comprising a magnet body including an R-T-B alloy and a coating layer on the magnet body, and including Cu on the magnet body. A first step of forming a layer; a second step of heating the magnet body and the layer to diffuse R from the magnet body into the layer; and quenching the heated magnet body and the layer; A first phase including an R-based alloy different from the R-T-B based alloy on the magnet element body, dispersed in a filler form in the first phase, including the R-Cu based alloy and the first phase And a third step of forming a coating layer having a second phase having a Cu content higher than that of the first phase. A method for producing a rare earth sintered magnet is provided.

  In the rare earth sintered magnet obtained by the above-described manufacturing method, a coating layer including two phases having different Cu (copper element) contents is formed on a magnet body including an RTB-based alloy. Yes. Among these phases, the first phase containing an R-based alloy and having a low Cu content contributes to improving the adhesion between the coating layer and the magnet body because it has excellent adhesion to the magnet body. On the other hand, the second phase containing the R—Cu-based alloy and having a higher Cu content than the first phase has an action of suppressing entry of hydrogen atoms that cause corrosion of the rare earth sintered magnet. Further, since such a second phase is dispersed in the first phase in the form of a filler, the diffusion paths of hydrogen atoms and other substances that cause corrosion are also lengthened. Since the coating layer having such characteristics is formed on the surface of the magnet body, the rare earth sintered magnet obtained by the production method of the present invention has excellent corrosion resistance.

  Moreover, in this invention, a rotary machine provided with the above-mentioned rare earth sintered magnet is provided. Since such a rotating machine includes the rare earth sintered magnet having the above-described characteristics, excellent performance can be maintained over a long period of time even when used in a harsh environment.

  ADVANTAGE OF THE INVENTION According to this invention, the rare earth sintered magnet excellent in corrosion resistance can be provided. In addition, by providing a rare earth sintered magnet having excellent corrosion resistance, a rotating machine capable of maintaining excellent performance over a long period of time can be provided.

It is a perspective view which shows typically suitable embodiment of the rare earth sintered magnet of this invention. It is the II-II sectional view taken on the line of the rare earth sintered magnet shown in FIG. It is an electron micrograph which expands and shows the cross section in suitable embodiment of the rare earth sintered magnet of this invention. It is a schematic cross section which expands and shows the cross section of the coating layer in suitable embodiment of the rare earth sintered magnet of this invention. It is a figure which shows the result of the elemental analysis by EDS (energy dispersive X-ray spectroscopy) of the coating layer in suitable embodiment of the rare earth sintered magnet of this invention. It is a perspective view showing a suitable embodiment of a rotating machine of the present invention typically.

  In the following, preferred embodiments of the present invention will be described with reference to the drawings as the case may be. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a perspective view schematically showing a rare earth sintered magnet of the present embodiment.

  FIG. 2 is a schematic cross-sectional view when the rare earth sintered magnet 100 shown in FIG. 1 is cut along the line II-II. The rare earth sintered magnet 100 has a magnet body 20 inside the rare earth sintered magnet 100 and a coating layer 40 provided so as to surround the magnet body 20.

  The magnet body 20 contains an RTB-based alloy as a main component. Here, R represents a rare earth element, T represents a transition element, and B represents a boron element. The RTB-based alloy includes one or more elements selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids belonging to Group 3 of the long-period periodic table as rare earth elements. Here, the lanthanoid is lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy). , Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

  In the R-T-B alloy, as R, at least one element selected from Nd, Pr, Ho and Tb, or La, Sm, Ce, Gd, Er, Eu, Tm, Yb, among those described above, is used. And at least one element selected from Y is preferred. In addition, the R-T-B alloy preferably contains at least one of iron element (Fe) and cobalt element (Co) as T, and more preferably contains Fe. Thereby, it can be set as the rare earth sintered magnet which is comparatively low cost and excellent in a magnetic characteristic.

As a suitable RTB-based alloy, an Nd-Fe-B-based alloy represented by Nd ₂ Fe ₁₄ B can be given. The rare earth sintered magnet 100 may contain a non-magnetic R-rich phase or B-rich phase other than Nd ₂ Fe ₁₄ B, a compound containing no rare earth element, or an alloy containing no rare earth element. The R-rich phase is a phase in which the element having the highest concentration among the elements constituting the phase is R, and the B-rich phase is a phase in which the element concentration of B is higher than that of the Nd ₂ Fe ₁₄ B phase. .

  The content ratio of the rare earth element in the magnet body 20 is preferably 8 to 40% by mass, and more preferably 15 to 35% by mass. If the content of the rare earth element is less than 8% by mass, the rare earth sintered magnet 100 having a high coercive force tends to be difficult to obtain. On the other hand, when the content of the rare earth element exceeds 40% by mass, the nonmagnetic R-rich phase increases, and the residual magnetic flux density (Br) of the rare earth sintered magnet 100 tends to decrease. The R-rich phase is a phase in which the element having the highest concentration among the elements constituting the phase is R.

  The content ratio of T in the magnet body 20 is preferably 42 to 90% by mass, and more preferably 60 to 80% by mass. When the content ratio of T is less than 42% by mass, the residual magnetic flux density of the rare earth sintered magnet 100 tends to decrease, and when it exceeds 90% by mass, the coercive force of the rare earth sintered magnet 100 tends to decrease.

  The proportion of Fe in T contained in the magnet body 20 is preferably 80 atomic% or more, more preferably 90 atomic% or more, and further preferably 100 atomic%. As a result, the rare earth sintered magnet 100 having low manufacturing cost and excellent magnetic properties can be obtained.

  The content ratio of B in the magnet body 20 is preferably 0.5 to 5% by mass. When the content ratio of B is less than 0.5% by mass, the coercive force of the rare earth sintered magnet 100 tends to decrease. On the other hand, when the B content exceeds 5% by mass, the B-rich nonmagnetic phase increases, so the Br of the rare earth sintered magnet 100 tends to decrease. A part of B may be substituted with one or more elements selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu). Thereby, the productivity of the rare earth sintered magnet 100 can be improved, and the production cost can be reduced.

  From the viewpoint of improving the coercive force of the rare earth sintered magnet 100, improving the productivity, and reducing the cost, the magnet body 20 is made of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese. (Mn), bismuth (Bi), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel It may contain at least one element selected from (Ni), silicon (Si), gallium (Ga), copper (Cu), hafnium (Hf), and the like.

  The magnet body 20 may contain at least one element selected from oxygen (O), nitrogen (N), carbon (C), calcium (Ca), and the like as an unavoidable impurity.

  FIG. 3 is an electron micrograph showing an enlarged cross section of the rare earth sintered magnet 100. The covering layer 40 provided so as to cover the surface of the magnet body 20 includes a first phase 42 and a second phase having a composition different from that of the first phase 42 dispersed in the first phase 42. 44. The magnet body 20 and the first phase 42 and the second phase 44 have different compositions. At the interface between the magnet body 20 and the coating layer 40, for example, a region in which crystal particles include an Nd—Fe—B alloy is used as the magnet body 20, and a region that does not substantially contain an Nd—Fe—B alloy is covered. It can be determined as layer 40.

  The first phase 42 contains an R-based alloy different from the RTB-based alloy as a main component. Here, R in the R-based alloy has the same meaning as R in the RTB-based alloy included in the magnet body 20 described above. The R alloy may be a rare earth alloy having a plurality of rare earth elements, or may be an R-Fe alloy. Specific examples of R alloys include Nd-Fe alloys, Nd-Pr alloys, Nd-Dy alloys, Nd-Pr-Dy alloys, Pr-Fe alloys, Nd-Dy-Fe alloys, Nd-Pr-Fe alloys. And Nd—Fe—Co alloy. Note that a smaller amount of Cu than the content of Cu in the second phase 44 may be dissolved in the R-based alloy in the first phase 42.

  On the other hand, the second phase 44 is a phase having a composition different from that of the first phase 42, and contains an R—Cu based alloy as a main component. Here, R is synonymous with R in the RTB-based alloy included in the magnet body 20 described above. Specific examples of R-Cu alloys include Nd-Cu alloys such as NdCu, Nd-Pr-Cu alloys, Nd-Dy-Cu alloys, Nd-Co-Cu alloys, and Nd-Fe-Cu alloys. It is done. Other elements such as Fe may be dissolved in the R—Cu alloy in the second phase 44.

  FIG. 4 is a schematic cross-sectional view showing a further enlarged cross section of the coating layer 40. The second phase 44 has a filler-like shape and is arranged in the first phase 42 in substantially the same direction. That is, the second phase 44 having a filler-like shape is dispersed in a striped manner with its longitudinal direction aligned in substantially the same direction. Thus, when the coating layer 40 has a striped structure, it is possible to further suppress diffusion of a substance that causes corrosion of the magnet body 20 from the surface of the coating layer 40 to the magnet body 20.

  FIG. 5 is a diagram illustrating an example of a result of elemental analysis of the coating layer 40 by EDS (energy dispersive X-ray spectroscopy). FIG. 5A is a diagram showing the result of elemental analysis of the first phase 42, and FIG. 5B is a diagram showing the result of elemental analysis of the second phase 44.

  The first phase 42 contains R (Nd, Pr), Fe, and Cu as shown in the elemental analysis result of FIG. The second phase 44 contains R (Nd, Pr), Fe, and Cu as shown in the elemental analysis result of FIG. The second phase 44 has a higher elemental ratio of Cu than the first phase 42. On the other hand, the element ratio of R is higher in the first phase 42 than in the second phase 44.

  Since the second phase 44 contains an alloy having Cu as a constituent element and the Cu content is higher than that of the first phase 42, the substance that causes corrosion of the magnet body 20 is rare earth sintered. It has the effect | action which suppresses entering from the exterior of the magnet 100. FIG. On the other hand, the first phase 42 has more R than the second phase 44. For this reason, the first phase 42 contributes to improving the adhesion between the magnet body 20 and the coating layer 40. To do.

  The content of Cu in the first phase 42 is preferably 0 to 4 atom%, more preferably 0 to 2 atom%, from the viewpoint of sufficiently increasing the adhesion between the magnet body 20 and the coating layer 40. It is. The content of Cu in the second phase 44 is preferably 30 to 60 atom%, more preferably 35 to 55 atom%, from the viewpoint of the rare earth sintered magnet 100 having further excellent corrosion resistance. Content of Cu (copper element) in the 1st phase 42 and the 2nd phase 44 is content when all the copper components (copper and copper alloy) contained in each phase are converted into a copper element. The Cu content in each phase can be determined by analyzing the EDS analysis result using a calibration curve. Further, the content of R in the first phase 42 obtained in the same manner is preferably 50 atom% or more from the viewpoint of the rare earth sintered magnet 100 having excellent adhesion to the magnet body 20.

  The EDS analysis can be performed using, for example, an EDS apparatus of a transmission electron microscope (TEM, manufactured by JEOL Ltd., trade name: JEM-2200FS). In addition, the striped structure of the coating layer 40 can be confirmed by using either a commercially available transmission electron microscope (TEM) or a scanning electron microscope (SEM). From these electron microscope images, the volume ratio of the first phase 42 and the second phase 44 in the coating layer 40 can be obtained.

  The difference between the Cu content in the first phase 42 and the Cu content in the second phase 44 is preferably 30 to 60 atom%, more preferably 35 to 55 atom%. By having the first phase 42 and the second phase 44 in which the difference in Cu content is in the above range, the adhesion and corrosion resistance of the magnet body 20 and the coating layer 40 can be made compatible at a higher level. .

  In the coating layer 40, the volume ratio of the second phase 44 to the first phase 42 is preferably 20 to 80% by volume, more preferably 30 to 70% by volume. By providing the coating layer 40 having the first phase 42 and the second phase 44 at such a volume ratio, the rare earth sintered magnet 100 having further excellent corrosion resistance can be obtained.

  The second phase 44 has a filler-like shape, and is preferably an average of 2 to 1000, more preferably 5 to 500, in an image showing a cross section of the coating layer 40 enlarged with a scanning electron microscope. It has an aspect ratio. By containing the filler-like second phase 44 having such an average aspect ratio, it is possible to sufficiently suppress the diffusion of substances that cause corrosion from the surface of the coating layer 40 toward the magnet body 20. can do.

  The average aspect ratio in the present specification is obtained as follows. In an image showing a cross section perpendicular to the interface between the magnet body 20 and the coating layer 40 enlarged with a scanning electron microscope, 500 first phases 42 are randomly extracted. Then, a straight line having the maximum length (referred to as L1) is obtained from straight lines connecting two different points on the contour of each first phase 42. Further, a length (referred to as L2) between two intersections between a straight line orthogonal to the straight line and the outline of the first phase 42 is obtained. The ratio of L1 and L2 (L1 / L2) obtained in each first phase 42 is the aspect ratio. If the number average value of the aspect ratios thus obtained is calculated, the average aspect ratio can be obtained.

  The thickness of the coating layer 40 is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, from the viewpoint of achieving both excellent magnetic properties and excellent corrosion resistance at a higher level.

  The magnet body 20 is a sintered body and has a plurality of crystal grains. Here, the crystal grains are made of an R-T-B alloy, but the grain boundary phase between the crystal grains often includes, for example, a nonmagnetic R-rich phase. Since the R-rich phase has low corrosion resistance, the corrosion of the magnet body 20 usually proceeds along the grain boundary phase containing the R-rich phase having low corrosion resistance. Therefore, the thickness of the coating layer 40 above the grain boundary phase exposed on the surface of the magnet body 20 is preferably larger than the thickness above the crystal grains. Thereby, the corrosion resistance can be further improved.

  Next, a preferred embodiment of the method for producing a rare earth sintered magnet of the present invention will be described. The manufacturing method of the present embodiment includes a preparation process for manufacturing a magnet body including an RTB-based alloy, a covering process for forming a layer containing Cu on the magnet body, a magnet body and a layer, A diffusion step of diffusing R from the magnet body into the layer, and quenching the heated magnet body and the layer to form an R-based alloy different from the RTB-based alloy from the layer. A coating layer comprising: a first phase including: a second phase containing an R-Cu-based alloy and having a Cu content higher than that of the first phase, dispersed in a filler form in the first phase Forming a cooling step. Details of each step will be described below.

  In the preparation step, the magnet body 20 is manufactured by a sintering method described below. First, a composition containing R, T and B in a predetermined ratio is cast to obtain an ingot. The obtained ingot is roughly pulverized to a particle size of about 10 to 100 μm using a stamp mill or the like, and then finely pulverized to a particle size of about 0.5 to 5 μm using a ball mill or the like to obtain a magnetic powder.

  Next, the obtained magnetic powder is preferably molded in a magnetic field to prepare a molded body. In this case, the applied magnetic field strength is preferably 800 kA / m or more, and the molding pressure is preferably about 100 to 500 MPa. Next, the prepared molded body is sintered at 1000 to 1200 ° C. for about 0.5 to 5 hours and rapidly cooled. In this way, a sintered body (magnet body) can be obtained. The sintering atmosphere is preferably an inert gas atmosphere such as argon gas.

  If necessary, the obtained sintered body may be processed into a predetermined shape. Examples of the processing method include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing. Such processing is not necessarily performed.

  In the covering step, a layer containing Cu is formed on the magnet body 20. Examples of the layer include a plated layer containing copper or a copper alloy formed by electroplating, a binder layer obtained by applying a paint containing a binder and copper or a copper alloy dispersed in the binder, and the like. . Among these layers, a copper plating layer is preferable from the viewpoint of efficiently forming a copper alloy on the coating layer 40. The content of Cu contained in the layer is preferably 50 atomic% or more, more preferably 70 atomic% or more, and further preferably 80 atomic% or more.

  When the layer containing copper is formed by electroplating, it is preferable to perform a pretreatment of the magnet body 20 before electroplating. Examples of the pretreatment include alkali degreasing treatment, acid washing treatment, and ultrasonic washing. By performing such pretreatment, the deposits on the surface of the magnet body are removed, and a layer with less thickness variation and defects can be formed.

  In the diffusion step, the magnet element body 20 having a copper-containing layer formed on the surface is heated to diffuse R and Fe from the magnet element body 20 into the layer. At this time, Cu contained in the layer may diffuse from the layer into the magnet body 20. From the viewpoint of sufficiently promoting the diffusion, the heating temperature is preferably 400 to 700 ° C., and the heating time is preferably 0.1 to 10 hours. When the heating temperature exceeds 700 ° C., the reaction between the magnet body 20 and the layer proceeds so much that the magnetic properties of the obtained rare earth sintered magnet tend to deteriorate. On the other hand, when the heating temperature is less than 400 ° C., the diffusion of each element tends to be difficult to proceed sufficiently.

  In the cooling step, the magnet body 20 and the layer heated to the above heating temperature are rapidly cooled. The cooling step may be rapid cooling from the heating temperature to room temperature (about 20 ° C.), or may be rapidly cooled at the beginning of cooling and gradually cooled after the temperature of the magnet body 20 and the layer is lowered to about 300 ° C., for example. Good. By rapid cooling, phase separation occurs in the layer, and a first phase containing an R-based alloy different from the R-T-B based alloy, and R-Cu dispersed in a filler form in the first phase. A coating layer 40 having a two-phase structure is formed, which includes a second phase containing a base alloy and having a Cu content higher than that of the first phase. The cooling rate during quenching is preferably 20 ° C./min or more, more preferably 30 ° C./min or more. If the cooling rate at the time of rapid cooling is too low, phase separation is difficult to occur, and it tends to be difficult to form the coating layer 40 having a two-phase structure. In addition, although there is no upper limit in particular in a cooling rate, about 300 degreeC / min may become an upper limit from the restrictions on an installation, etc. In addition, the cooling rate here means the average temperature-fall rate until it cools to 300 degreeC from the heating temperature in a diffusion process.

  The rare earth sintered magnet 100 having the magnet body 20 and the coating layer 40 covering the magnet body 20 can be obtained by the manufacturing method described above. Since the rare earth sintered magnet 100 includes the coating layer 40 having a two-phase structure with different Cu contents, the corrosion resistance is excellent. Such a rare earth sintered magnet 100 can maintain excellent magnetic properties over a long period of time even when used in an environment where a corrosive substance exists. The rare earth sintered magnet 100 of this embodiment having such characteristics is suitably used as a permanent magnet for a rotating machine that is required to have excellent corrosion resistance, for example.

  FIG. 6 is an explanatory diagram showing the internal structure of the rotating machine (permanent magnet rotating machine) of the present embodiment. The rotating machine 200 of this embodiment is a permanent magnet synchronous rotating machine (SPM rotating machine), and includes a cylindrical rotor 50 and a stator 30 disposed inside the rotor 50. The rotor 50 is provided with a plurality of rare earth sintered magnets 100 such that the north pole and the south pole are alternately arranged along the inner peripheral surface of the cylindrical core 52 and the cylindrical core 52. The stator 30 has a plurality of coils 32 provided along the inner peripheral surface. The coil 32 and the rare earth sintered magnet 100 are arranged to face each other.

  The rotating machine 200 includes the rare earth sintered magnet 100 according to the above embodiment in the rotor 50. Since the rare earth sintered magnet 100 is excellent in corrosion resistance, it is possible to sufficiently suppress the deterioration of magnetic characteristics over time. Therefore, the rotating machine 200 can maintain excellent performance for a long time. The rotating machine 200 can be manufactured by a normal method using normal rotating machine parts for parts other than the rare earth sintered magnet 100.

  The rotating machine 200 may be an electric motor (motor) that converts electrical energy into mechanical energy by the interaction between the field generated by the electromagnet generated by energizing the coil 32 and the field generated by the rare earth sintered magnet 100. Good. The rotating machine 200 may be a generator that converts mechanical energy to electrical energy by electromagnetic induction interaction between the field magnet of the rare earth sintered magnet 100 and the coil 32.

  Examples of the rotating machine 200 that functions as an electric motor (motor) include a permanent magnet DC motor, a linear synchronous motor, a permanent magnet synchronous motor (SPM motor), and a permanent magnet synchronous motor (IPM motor). The electric motor (motor) may be, for example, a reciprocating motor such as a voice coil motor or a vibration motor. Examples of the rotating machine 200 that functions as a generator include a permanent magnet synchronous generator, a permanent magnet commutator generator, and a permanent magnet AC generator.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments. For example, the rare earth sintered magnet of the present invention may further have a surface layer different from the coating layer 40 containing copper or other components on the coating layer.

  The contents of the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.

<Preparation of rare earth sintered magnet>
Example 1
An ingot made of an Nd—Pr—Dy—Co—Al—Cu—B—Fe alloy having the following composition was prepared by powder metallurgy. In addition, the following composition shows content on the mass basis of each element.

Nd: 22.5% by mass
Pr: 5.2 mass%
Dy: 2.7% by mass
Co: 0.5% by mass
Al: 0.3% by mass
Cu: 0.07 mass%
B: 1.0 mass%
Fe: balance

  After roughly pulverizing the ingot, jet milling with an inert gas was performed to obtain a powder having an average particle size of about 3.5 μm. The obtained powder was filled in a mold and press-molded in a magnetic field to produce a molded body. Next, the compact was sintered under vacuum at a holding temperature of 1100 ° C. and a holding time of 3 hours, and then heat treated to obtain a sintered body. The obtained sintered body was cut into a size of 10 mm × 8 mm × 1 mm and processed to obtain a rectangular parallelepiped magnet element.

  After barrel-polishing the obtained magnet body, it was immersed in an aqueous nitric acid solution (nitric acid concentration: 2 mass%) for 2 minutes and washed with ultrasonic water. A 1 μm copper film was formed by electroplating on the surface of the magnet body thus acid-washed. The magnet body on which the copper film was formed was subjected to a heat treatment of heating at 540 ° C. for 1 hour in an argon gas atmosphere. Then, the magnet body on which the copper film was formed was cooled to 300 ° C. at an average cooling rate of 50 ° C./min, and then allowed to cool to room temperature. Thus, the rare earth sintered magnet of Example 1 was obtained.

(Example 2)
In the same manner as in Example 1, a copper film was formed on the surface of the magnet body. A rare earth sintered magnet was produced in the same manner as in Example 1 except that the magnet body on which the copper film was formed was subjected to a heat treatment of heating at 550 ° C. for 10 minutes in an argon gas atmosphere. This was used as the rare earth sintered magnet of Example 2.

(Comparative Example 1)
After obtaining a magnet body in the same manner as in Example 1, barrel polishing, immersion in an aqueous nitric acid solution, and ultrasonic water washing were performed in the same manner as in Example 1. This was used as the rare earth sintered magnet of Comparative Example 1.

(Comparative Example 2)
After obtaining a magnet body in the same manner as in Example 1, barrel polishing, immersion in an aqueous nitric acid solution, and ultrasonic water washing were performed in the same manner as in Example 1. In the same manner as in Example 1, a 1 μm copper film was formed by electroplating. This was used as the rare earth sintered magnet of Comparative Example 2.

(Comparative Example 3)
In the same manner as in Example 1, a copper film was formed on the surface of the magnet body and subjected to heat treatment. Thereafter, a rare earth sintered magnet was produced in the same manner as in Example 1 except that the material was cooled to room temperature at a cooling rate of 1 ° C./min. This was used as the rare earth sintered magnet of Comparative Example 3.

<Structure and composition analysis of rare earth sintered magnet>
The rare earth sintered magnets of each example and each comparative example were cut and the cut surface was polished with a cross section polisher. When the polished surface was observed with a scanning electron microscope, in the rare earth sintered magnet of Example 1, the coating layer having a thickness of 100 nm to 2 μm on the surface of the magnet body containing the R—T—B system alloy as a main component. It was confirmed that was formed.

  When elemental analysis of the coating layer was performed using an EDS (energy dispersive X-ray fluorescence spectrometer), it was confirmed that the coating layer contained Nd, Fe, and Cu. Further, the coating layer contains Nd, Pr and Fe, a portion having a high Cu content (second phase), Nd, Pr and Fe, and the Cu content is lower than that of the second phase. Part (first phase).

  From the image by a scanning electron microscope, it was confirmed that the coating layer has a striped structure in which the filler-like second phase is dispersed in the first phase. The volume ratio of the first phase in the coating layer was 51%, and the volume ratio of the second phase was 49%.

  Similarly to Example 1, the rare earth sintered magnet of Example 2 contains Nd, Pr, and Fe on the surface of the magnet body containing the R-T-B alloy as a main component, and contains Cu. Is provided with a coating layer having a high part (second phase) and a part (first phase) containing Nd, Pr and Fe and having a lower Cu content than the second phase. It was. Further, the coating layer of Example 2 also had a striped structure in which the filler-like second phase was dispersed in the first phase. The rare earth sintered magnet of Example 2 had a copper plating film on the coating layer.

  On the other hand, the rare earth sintered magnet of Comparative Example 1 did not have a coating layer, and the coating layer of the rare earth sintered magnet of Comparative Example 2 was made of a copper plating film. Moreover, the coating layer of the rare earth sintered magnet of Comparative Example 3 did not have the striped structure as in Example 1.

<Corrosion resistance evaluation>
The pressure cooker test (PCT) which hold | maintains the rare earth sintered magnet of each Example and each comparative example for 500 hours at the temperature of 120 degreeC in the atmosphere where saturated steam exists. The mass of the rare earth sintered magnet before and after PCT was measured, and the difference in mass between the two was used as the mass reduction amount of the rare earth sintered magnet. The mass reduction rate was calculated by dividing the mass reduction amount by the mass before PCT. The results are shown in Table 1.

  As shown in Table 1, the rare earth sintered magnet of Example 1 did not lose its mass even after 500 hours had passed since the start of PCT. On the other hand, it was confirmed that the rare earth sintered magnet of Comparative Example 1 had a reduced mass at the time when 100 hours had passed after starting the PCT. And after 500 hours progress, the mass reduction | decrease rate was 2.7%. In addition, it was confirmed that the rare earth sintered magnet of Comparative Example 2 had a reduced mass when 140 hours had passed after starting the PCT. And after 500 hours progress, the mass reduction | decrease rate was 9.7%.

  It was confirmed that the rare earth sintered magnet of Comparative Example 3 in which the cooling rate after the heat treatment was slowed was inferior to Examples 1 and 2. This is because, in the rare earth sintered magnet obtained by slow cooling after the heat treatment, a coating layer having a striped structure in which two types of phases having different copper element contents are dispersed is not formed. Yes.

  ADVANTAGE OF THE INVENTION According to this invention, the rare earth sintered magnet excellent in corrosion resistance can be provided. In addition, it is possible to provide a rotating machine capable of maintaining excellent performance over a long period of time.

  DESCRIPTION OF SYMBOLS 20 ... Magnet body, 30 ... Stator, 32 ... Coil, 40 ... Covering layer, 42 ... First phase, 44 ... Second phase, 50 ... Rotor, 52 ... Core, 100 ... Rare earth sintered magnet, 200 ... Rotating machine.

Claims (5)

A magnet body including an R-T-B alloy, and a coating layer on the magnet body;
The coating layer has a first phase and a second phase dispersed in a filler form in the first phase,
The first phase includes an R-based alloy different from the RTB-based alloy, the second phase includes an R-Cu-based alloy, and has a Cu content higher than that of the first phase. High rare earth sintered magnet.
(However, R represents a rare earth element, T represents a transition element, B represents a boron element, and Cu represents a copper element.)   The rare earth sintered magnet according to claim 1, wherein a volume ratio of the second phase to the first phase is 20 to 80% by volume.   3. The rare earth sintered magnet according to claim 1, wherein the difference between the Cu content in the first phase and the Cu content in the second phase is 30 to 60 atomic%. A method for producing a rare earth sintered magnet comprising a magnet body including an R-T-B alloy and a coating layer on the magnet body,
A first step of forming a layer containing Cu on the magnet body;
A second step of heating the magnet body and the layer to diffuse R from the magnet body into the layer;
The heated magnet body and the layer are quenched, and a first phase containing an R-based alloy different from the RTB-based alloy on the magnet body, and the first phase A third step of forming the coating layer having a second phase that is dispersed in a filler form and includes an R-Cu-based alloy and has a Cu content higher than that of the first phase. And manufacturing method of rare earth sintered magnet.
(However, R represents a rare earth element, T represents a transition element, B represents a boron element, and Cu represents a copper element.)   A rotating machine comprising the rare earth sintered magnet according to any one of claims 1 to 3.