JP2018093109A - Rare earth cobalt-based permanent magnet and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare earth cobalt-based permanent magnet which can be manufactured easily, and has a good mechanical strength.SOLUTION: A rare earth cobalt-based permanent magnet (10) contains R:23-27%, Cu:3-6% (excepting 6%), Fe:10-25%, Zr:1.5-4.0%, and the reminder consisting of Co and inevitable impurities, where the element R is a rare earth element including at least Sm. The rare earth cobalt-based permanent magnet (10) has a base layer (1) including a first cell phase, and a surface oxide layer (2) covering the base layer (1).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a rare earth cobalt permanent magnet and a method for producing the same.

  Patent Document 1 discloses a method for producing a plated samarium cobalt magnet. Specifically, a samarium-cobalt magnet alloy powder is molded under pressure to obtain a green compact, and then the green compact is sintered at a predetermined temperature in an atmosphere of argon gas. Subsequently, nickel plating of a predetermined thickness is performed by the steps of alkali degreasing, water washing, neutralization, water washing, activation, water washing, nickel (Ni) plating, water washing, and a predetermined heat treatment is performed in an atmosphere of argon gas. . The samarium cobalt magnet described above is manufactured through these steps. Such a samarium cobalt magnet has good mechanical strength.

Japanese Patent Laid-Open No. 08-181016

  Such a method for producing a samarium cobalt magnet requires heating in an atmosphere in an inert gas such as nickel plating or argon gas, and there is room for improvement in ease of production.

  The present invention provides a rare earth cobalt-based permanent magnet that can be easily manufactured and has good mechanical strength.

Rare earth cobalt permanent magnet according to the present invention,
When the element R is a rare earth element containing at least Sm,
In mass%, R: 23-27%, Cu: 3-6% (excluding 6%), Fe: 10-25%, Zr: 1.5-4.0%, the balance being Co And a rare earth cobalt-based permanent magnet comprising inevitable impurities,
A base layer comprising a first cell phase;
A surface oxide layer covering the base layer.
Such a configuration can be manufactured by heating in an atmosphere containing oxygen. Therefore, it can manufacture easily, without requiring a plating process or the heating process in inert gas atmosphere. In addition, an oxide layer can be formed on the surface, the progress of fracture starting from microcracks can be suppressed, and good mechanical strength is achieved.
Furthermore, the Fe content in the surface oxide layer may be higher than the Fe content in the base layer. The surface oxide layer may have a thickness in the range of 50 to 500 nm.
In addition, the base layer includes a striped layer in contact with the surface oxide layer, and the striped layer extends along the interface with the surface oxide layer. May be included. Further, the Fe content in the linear portion may be higher than the Fe content in the base layer.
In addition, a crack may be generated in the base layer, and the base layer may further include an internal oxide layer that covers the crack. Furthermore, the inner oxide layer may fill the crack.
The base layer includes a transition layer in contact with the striped layer, and the transition layer includes a plurality of second linear portions extending along an interface with the striped layer, and a second layer The cell phase may be provided.

On the other hand, the method for producing a rare earth cobalt-based permanent magnet according to the present invention is as follows.
When the element R is a rare earth element containing at least Sm,
In mass%, R: 23-27%, Cu: 3-6% (excluding 6%), Fe: 10-25%, Zr: 1.5-4.0%, the balance being Co And a method for producing a rare earth cobalt based permanent magnet using a permanent magnet body made of inevitable impurities,
A step of forming a surface oxide layer on the permanent magnet body by heating and holding the permanent magnet body at a heat treatment temperature of 200 to 600 ° C. in an atmosphere having an oxygen partial pressure of 1 to 100%.
According to such a configuration, a rare earth cobalt permanent magnet having good mechanical strength can be manufactured by heating in an atmosphere having an oxygen partial pressure of 1% or more. Therefore, it can manufacture easily, without requiring a plating process and the heating process in inert gas atmosphere.
Furthermore, in the step of forming the surface oxide layer on the permanent magnet body, the permanent magnet body may be heated and held in an air atmosphere. In the step of forming the surface oxide layer on the permanent magnet body, the heat treatment temperature may be 300 to 510 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, while being easy to manufacture, the rare earth cobalt permanent magnet which has favorable mechanical strength can be provided.

FIG. 3 is a schematic diagram showing a cross section near the surface of the rare earth cobalt-based permanent magnet according to the first embodiment. It is a schematic diagram which shows the cross section of the surface vicinity of the example of a change of the rare earth cobalt permanent magnet concerning Embodiment 1. FIG. It is a schematic diagram which shows the cross section of the surface vicinity of the example of a change of the rare earth cobalt permanent magnet concerning Embodiment 1. FIG. It is a schematic diagram which shows the cross section of the surface vicinity of the example of a change of the rare earth cobalt permanent magnet concerning Embodiment 1. FIG. 3 is a flowchart of a method for manufacturing the rare earth cobalt-based permanent magnet according to the first embodiment. 2 is a photograph showing a microstructure of a cross section near the surface of the permanent magnet of Example 1. FIG. 4 is a photograph showing a microstructure of a cross section near the surface of a permanent magnet of Example 2. FIG. 6 is a photograph showing a microstructure of a cross section in the vicinity of the surface of the permanent magnet of Example 3. It is an image by the DF-STEM of the permanent magnet of Example 3. It is the image by the elemental mapping of the surface of the permanent magnet of Example 3. It is the image by the elemental mapping of the surface of the permanent magnet of Example 3. It is the image by the elemental mapping of the surface of the permanent magnet of Example 3. It is the image by the elemental mapping of the surface of the permanent magnet of Example 3. It is the image by the elemental mapping of the surface of the permanent magnet of Example 3. It is the image by the elemental mapping of the surface of the permanent magnet of Example 3. It is the image by the elemental mapping of the surface of the permanent magnet of Example 3. It is a cross-sectional photograph which shows each part which measured the microstructure of the cross section in the surface vicinity of Example 3, and chemical composition. 4 is a photograph showing a cross-sectional microstructure in the vicinity of the surface of the permanent magnet of Comparative Example 1;

  The present inventors paid attention to a phenomenon in which microcracks are generated by machining when processing a samarium-cobalt magnet into a product shape, and when the bending compressive stress is applied, the microcracks start and break easily. Furthermore, in order to improve the mechanical strength of the samarium-cobalt magnet, it was recalled that the influence on the mechanical strength caused by these microcracks was removed. The inventors of the present invention have intensively studied the manufacturing method of the heat treatment conditions such as the atmosphere and the heating temperature, the configuration of the samarium cobalt magnet, etc., and have come up with the present invention.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

(Embodiment 1)
With reference to FIG. 1, the rare earth cobalt-based permanent magnet according to the first embodiment will be described. FIG. 1 is a schematic diagram showing a cross section near the surface of a rare earth cobalt-based permanent magnet according to the first embodiment. For the sake of clarity, hatching is not shown in FIG.

The rare earth cobalt-based permanent magnet 10 shown in FIG. 1 is in mass%, R: 23 to 27%, Cu: 3 to 6% (excluding 6%), Fe: 10 to 25%, Zr: 1. It contains 5 to 4.0%, and the balance consists of Co and inevitable impurities. Here, R is a rare earth element, and includes at least Sm among the rare earth elements. Examples of rare earth elements other than Sm include Pr, Nd, Ce, and La. The rare earth cobalt permanent magnet 10 contains an intermetallic compound mainly composed of rare earth cobalt. Examples of such intermetallic compounds include SmCo ₅ and Sm ₂ Co ₁₇ . The rare earth cobalt permanent magnet 10 has a metal structure including crystal grains.

The rare earth cobalt-based permanent magnet 10 includes a base layer 1 and a surface oxide layer 2. The base layer 1 includes crystal grains, and the crystal grains include a cell phase containing Sm ₂ Co ₁₇ . The crystal grains may further include a cell wall containing SmCo ₅ and a Zr-containing plate-like phase surrounding the cell phase.

  The surface oxide layer 2 covers the base layer 1. The surface oxide layer 2 is preferably filled with microcracks on the surface of the base layer 1. The thickness of the surface oxide layer 2 is in the range of 50 nm to 500 nm, for example. In addition, it is confirmed that the thickness of the surface oxide layer 2 obtained by the method for manufacturing the rare earth cobalt based permanent magnet according to the first embodiment to be described later is at least in the range of 50 nm to 500 nm. Further, the surface oxide layer 2 may include a concentrating part 21 in which a specific element such as Co or Cu is concentrated. The Co content in the concentrated portion 21 where Co is concentrated is higher than the Co content in the surface oxide layer 2, and is, for example, 90% to 99% in mass%. The Fe content of the surface oxide layer 2 is higher than the Fe content of the base layer 1.

  The rare earth cobalt permanent magnet 10 has good mechanical properties. One reason for this is that since the surface oxide layer 2 covers the base layer 1, the surface oxide layer 2 of the base layer 1 and the contact surface 11 are filled with minute cracks, and the destruction starting from the minute cracks is suppressed. It is thought to do.

  The rare earth cobalt permanent magnet 10 can be widely used as various parts of a timepiece, an electric motor, an instrument, a communication device, a computer terminal, a speaker, a video disk, a sensor, and other devices. In addition, since the rare earth cobalt permanent magnet has good mechanical strength, it is particularly expected to be applied to an ignition coil that tends to be thinner than other products.

(Example of change)
Next, each modified example of the rare earth cobalt permanent magnet 10 will be described with reference to FIGS. 2 to 4 are schematic views showing a cross section near the surface of a modified example of the rare earth cobalt-based permanent magnet according to the first embodiment. For the sake of clarity, hatching is not shown in FIGS.

(Modification 1)
A rare earth cobalt based permanent magnet 20 shown in FIG. 2 is a modification of the rare earth cobalt based permanent magnet 10. The rare earth cobalt permanent magnet 20 has the same configuration as the rare earth cobalt permanent magnet 10 except that the striped layer 3 is provided. The striped layer 3 is in direct contact with the surface oxide layer 2. Striped layer 3 includes a plurality of linear portions 31 extending along the interface with surface oxide layer 2 and a cell phase having the same configuration as the cell phase included in base layer 1. The plurality of linear portions 31 show a striped pattern in the cross section of the rare earth cobalt permanent magnet 20. The linear portion 31 is considered to have a film-like body or a shape close thereto in the rare earth cobalt-based permanent magnet 20. The linear part 31 is an oxide. The Fe content of the linear portion 31 is higher than the Fe content of the base layer 1.

  Since the rare earth cobalt permanent magnet 20 includes the surface oxide layer 2 similarly to the rare earth cobalt permanent magnet 10, it has good mechanical strength. Since the rare earth cobalt permanent magnet 20 includes the striped layer 3, it can have higher mechanical strength than the rare earth cobalt permanent magnet 10.

(Modification 2)
A rare earth cobalt based permanent magnet 30 shown in FIG. 3 is a modified example of the rare earth cobalt based permanent magnets 10 and 20. The rare earth cobalt based permanent magnet 30 has the same configuration as the rare earth cobalt based permanent magnet 20 except that the inner oxide layer 6 is provided. The rare earth cobalt based permanent magnet 30 has a crack 5. The crack 5 may be on the surface or inside of the rare earth cobalt-based permanent magnet 30, the base layer 1, the surface oxide layer 2, or the striped layer 3, and the number thereof may be plural. The size, shape and direction of the crack 5 are various. The rare earth cobalt-based permanent magnet 30 includes a striped layer 3 and an internal oxide layer 6, and the internal oxide layer 6 covers the crack 5. The internal oxide layer 6 is preferably filled with microcracks on the surface of the crack 5. The internal oxide layer 6 is preferably filled with the cracks 5. In other words, the inner oxide layer 6 is preferably filled to fill the crack 5.

  The rare earth cobalt permanent magnet 30 has good mechanical strength due to the above-described configuration. Here, it is considered that the rare earth cobalt-based permanent magnet 30 has a crack 5 and may have a reduced mechanical strength. However, the rare earth cobalt-based permanent magnet 30 includes the inner oxide layer 6. Therefore, the mechanical strength reduced by the crack 5 can be sufficiently recovered or reinforced. Moreover, since the rare earth cobalt-based permanent magnet 30 includes the surface oxide layer 2 and the striped layer 3 similarly to the rare earth cobalt-based permanent magnet 20, it has good mechanical strength.

(Modification 3)
A rare earth cobalt permanent magnet 40 shown in FIG. 4 is a modification of the rare earth cobalt permanent magnets 10, 20, and 30. The rare earth cobalt-based permanent magnet 40 has the same configuration as the rare earth cobalt-based permanent magnet 30 except that the transition layer 4 is provided. The transition layer 4 is in contact with the striped layer 3, a plurality of linear portions 31 extending along the interface with the striped layer 3, and a cell phase having the same configuration as the cell phase included in the base layer 1 Including. The amount of the linear portion 31 included in the transition layer 4 is smaller than the amount of the linear portion 31 included in the striped layer 3. The transition layer 4 is located between the striped layer 3 and the base layer 1 so that the amount of the linear portion 31 in the transition layer 4 decreases from the striped layer 3 side toward the base layer 1 side. It tends to transition. While the base layer 1 includes the cell phase, the base layer 1 hardly includes the linear portion 31.

  Since the rare earth cobalt-based permanent magnet 40 includes the inner oxide layer 6 similarly to the rare earth cobalt-based permanent magnet 30, the mechanical strength reduced by the crack 5 can be sufficiently recovered or reinforced. Since the rare earth cobalt based permanent magnet 40 includes the surface oxide layer 2 and the striped layer 3, the rare earth cobalt based permanent magnet 40 has good mechanical strength like the rare earth cobalt based permanent magnet 20. Since the rare earth cobalt permanent magnet 40 includes the transition layer 4, it can have higher mechanical strength than the rare earth cobalt permanent magnet 30.

(Production method)
Next, with reference to FIG. 5, the manufacturing method of the permanent magnet concerning Embodiment 1 is demonstrated. FIG. 5 is a flowchart of the method for manufacturing the rare earth cobalt-based permanent magnet according to the first embodiment.

  First, rare earth elements, pure Fe, pure Cu, pure Co, and pure Zr are prepared as raw materials, and these are blended so as to have the above-described predetermined composition (raw material blending step S1). Here, a mother alloy containing Zr may be used instead of pure Zr. The mother alloy is a binary alloy usually made of two kinds of metal elements and used as a melting raw material. Further, the mother alloy containing Zr has a component composition that has a melting point lower than the melting point of pure Zr of 1852 ° C. The melting point of the master alloy containing Zr is preferably equal to or lower than the temperature at which the rare earth cobalt permanent magnet according to the first embodiment is melted, that is, 1600 ° C. or lower, more preferably 1000 ° C. or lower.

  Examples of the mother alloy containing Zr include FeZr alloy and CuZr alloy. Since the FeZr alloy and the CuZr alloy have a low melting point, Zr is preferably uniformly dispersed in the structure of the ingot described later. Therefore, it is preferable that the FeZr alloy and the CuZr alloy have a eutectic composition or a composition close to the eutectic composition because the melting point is suppressed to 1000 ° C. or lower. Specifically, the FeZr alloy is, for example, an Fe 20% Zr 80% alloy. The Fe 20% Zr 80% alloy is mass% and contains 75 to 85% of Zr, with the balance being Fe and inevitable impurities. The CuZr alloy is, for example, a Cu 50% Zr 50% alloy. The Cu 50% Zr 50% alloy is mass% and contains 45 to 55% of Zr, with the balance being Cu and unavoidable impurities.

Then, the blended raw material is charged into an alumina crucible, melted in a high-frequency melting furnace in a vacuum atmosphere of 1 × 10 ⁻² Torr or less or an inert gas atmosphere, and cast into a mold. (Ingot casting step S2). The casting method is, for example, a mold casting method called a book mold method. In addition, you may heat-process the obtained ingot for about 1 to 20 hours at solution temperature. It is preferable to perform this heat treatment because the ingot structure is made more uniform.

  Next, the obtained ingot is pulverized to obtain a powder having a predetermined average particle size (powder generation step S3). Typically, first, the obtained ingot is coarsely pulverized, and the coarsely pulverized ingot is finely pulverized in an inert atmosphere using a jet mill or the like to be powdered. The average particle diameter (d50) of the powder is, for example, 1 to 10 μm. The average particle size (d50) is the particle size at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method.

Next, the obtained powder is press-molded by pressing the powder perpendicularly to the magnetic field direction in a predetermined magnetic field to obtain a compact (press molding step S4). Here, as press molding conditions, a magnetic field is 15 kOe or more, for example, and the pressure value of press molding is 0.5-2.0 ton / cm < ² > (= 49-196 MPa), for example. Depending on the product, even if the magnetic field is 15 kOe (= 1193.7 kA / m) or less, the above-described powder may be pressed in parallel to the magnetic field direction and press-molded. The conversion between the non-SI unit and the SI unit may be performed using the following conversion formulas 1 to 4, for example.
1 [kOe] = 10 ³ / 4π [kA / m] (... Conversion formula 1)
1 [MGOe] = 10 ² / 4π [kJ / m ³ ] (... conversion formula 2)
1.0 [ton / cm ² ] = 98.0665 [MPa] (... Conversion formula 3)
1.0 [Torr] = 133.32 [Pa] (... Conversion formula 4)

Next, the compact is heated to a sintering temperature in a vacuum atmosphere of 1 × 10 ⁻² (= 1.332 Pa) Torr or less, or in an inert atmosphere, or in a vacuum and inert atmosphere of 1 × 10 ⁻² Torr or less. And sintering (sintering step S5). The sintering temperature is, for example, 1150 to 1250 ° C.

  Subsequently, the compact is subjected to a solution treatment at a solution temperature lower by 20 ° C. to 50 ° C. than the sintering temperature under the same atmospheric conditions (solution treatment step S6). The solution time is, for example, 2 to 10 hours. In addition, you may change suitably according to the structure | tissue of the obtained molded object, and the target magnetic characteristic. When the solution treatment time is longer than the lower limit time, the component composition becomes sufficiently uniform. On the other hand, if the solution treatment time is shorter than the upper limit time, the volatilization amount of Sm contained in the compact is suppressed. Thereby, it can suppress that a difference arises in the component composition of the inside of a molded object, and the surface, and can suppress the deterioration of the magnetic characteristic as a permanent magnet.

  Note that it is preferable to perform the sintering step S5 and the solution treatment step S6 in succession because mass productivity is improved. When the sintering step S5 and the solution treatment step S6 are performed continuously, the temperature is lowered from the sintering temperature to the solution treatment temperature at a low temperature decrease rate, for example, 0.2 to 5 ° C./min. It is preferable that the rate of temperature decrease is low because Zr can be more reliably dispersed and uniformly distributed in the metal structure of the compact.

  Next, the solution-treated sintered body is rapidly cooled, for example, at a cooling rate of 100 ° C./min (rapid cooling step S7). Further, while maintaining the same atmospheric conditions, heat and hold at a temperature of 700 to 870 ° C. for 1 hour or longer, and subsequently 0.2 to 5 ° C. until it drops to at least 600 ° C., preferably to 400 ° C. or less. Cooling is performed at a cooling rate of / min (aging process step S8). When the aging-treated sintered body is magnetized, a permanent magnet body is formed.

  Next, the formed permanent magnet body is processed into a product shape (product shape processing step S9). Specifically, the permanent magnet body is changed to a product shape by performing processing such as polishing and cutting on the permanent magnet body as necessary. Here, in this step, when the permanent magnet body is polished or cut, chipping and minute cracks often occur on the surface and inside of the permanent magnet body. The mechanical strength of the permanent magnet body decreases due to such chipping and minute cracks.

  Finally, the permanent magnet body is heated and held within the range of the heat treatment temperature of 200 to 600 ° C. in the atmosphere or in an atmosphere having an oxygen partial pressure of 1 to 100% (oxide layer formation heat treatment step S10). In this step, examples of the gas other than oxygen in the atmosphere include nitrogen gas and argon gas. The oxygen partial pressure in the atmosphere is, for example, 20 to 22%. The heating temperature is preferably in the range of 300 to 510 ° C, more preferably in the range of 350 to 450 ° C. By passing through this step, a surface oxide layer can be formed near the surface of the permanent magnet body. Similarly, at least one of a striped layer, an internal oxide layer, and a transition layer can be formed in the vicinity of the surface of the permanent magnet body according to various conditions of this step.

  Through the above steps, the rare earth cobalt based permanent magnet according to the first embodiment is obtained. In the oxide layer forming heat treatment step S10 of this step, the permanent magnet body is heated and held at a predetermined heat treatment temperature in the atmosphere or in an atmosphere having an oxygen partial pressure of 1 to 100%, thereby forming an oxide layer. As a result, the mechanical strength, which is reduced by processing the permanent magnet body in the product shape processing step S9, can be recovered or reinforced. That is, it is not necessary to heat and hold the permanent magnet body in an inert gas atmosphere, and a permanent magnet having good mechanical strength can be manufactured using a simpler apparatus.

  In the above-described manufacturing method, casting is performed using a mold in the ingot casting step S2. However, casting can also be performed using a strip casting method. In the strip casting method, a molten metal is dropped onto a copper roll to form, for example, a flake-like body having a thickness of 1 mm. The rare earth cobalt-based permanent magnet manufactured using the above-described manufacturing method, that is, the ingot casting step S2, has a better saturation magnetic flux density Br than the rare earth cobalt-based permanent magnet manufactured using the strip cast method. The squareness shown by the demagnetization curve is also good.

(Chemical composition)
Next, the reason for determining the chemical composition of the rare earth cobalt permanent magnet according to the first embodiment will be described.

  In the rare earth cobalt-based permanent magnet according to the first embodiment, if the content of the element R is 23% by mass or more, a certain squareness can be ensured in the demagnetization curve, and the magnetic characteristics can be improved. This is to ensure. Further, when the content of the element R is 27% by mass or less, a certain saturation magnetic flux density Br is ensured. Therefore, the content of the element R is in the range of 23% or more and 27% or less in mass%.

  If the Cu content is 3% by mass or more, a constant coercive force iHc can be secured, and if it is less than 6%, a Curie point and a constant saturation magnetic flux density Br are secured. Therefore, the Cu content is within a range of 3% or more and less than 6% by mass%.

  If the Fe content is 10% by mass or more, a constant saturation magnetic flux density Br can be secured, and if it is 25% or less, a constant coercive force iHc can be secured. Therefore, the content of Fe is in a range of 10% to 25% in mass%.

  When the content of Zr is 1.5% or more and 4% or less in terms of mass%, a certain coercive force iHc and energy product (BH) m can be secured. Therefore, the content of Zr is in the range of 1.5% to 4% by mass.

  By the way, as described above, in the method for manufacturing the rare earth cobalt permanent magnet according to the first embodiment, the surface oxide layer is formed in the oxide layer forming heat treatment step S10 (see FIG. 5). The formed surface oxide layer fills at least micro cracks on the surface of the base layer, so that the mechanical strength reduced by processing the permanent magnet body in the product shape processing step S9 can be recovered or reinforced. can do. These are considered to be unique phenomena in the rare earth cobalt-based permanent magnet according to the first embodiment having the above-described chemical composition.

  Further, as described above, in the method of manufacturing the rare earth cobalt based permanent magnet according to the first embodiment, the cell phase corresponding to the cell phase of the crystal grains of the base layer 1 (see FIG. 1) and the striped layer 3 A striped layer corresponding to (see FIG. 2) is formed. This is also considered to be a unique phenomenon in the rare earth cobalt-based permanent magnet according to the first embodiment having the above-described chemical composition.

(Examples 1-5)
Next, experiments conducted for Examples 1 to 5 and Comparative Examples 1 to 5 for the rare earth cobalt permanent magnet according to the first embodiment will be described.

Examples 1 to 5 were manufactured using the same manufacturing method as that described above. Specifically, in the raw material blending step S1 (see FIG. 5), the target composition is mass%, Sm: 25.0%, Cu: 4.5%, Fe: 20.0%, Zr: 2.4% The balance was Co. As a mother alloy containing Zr, an Fe 20% Zr 80% alloy was used. In the ingot casting step S2, the atmospheric condition was a vacuum atmosphere of 1 × 10 ⁻² Torr or less. Further, the ingot obtained in the ingot casting step S2 was heated and held at 1170 ° C. for 15 hours to perform heat treatment. In the powder generation step S3, the coarsely pulverized ingot was finely pulverized in an inert atmosphere using a jet mill to generate a powder having an average particle diameter (d50) of 6 μm. In press molding step S4, press molding is performed using a mold under the conditions of a magnetic field of 15 kOe and a press molding pressure of 1.0 ton / cm ² , and the powder is formed into a rectangular parallelepiped having a length of 100 mm, a width of 50 mm, and a height of 50 mm. Molded. In the sintering step S5, sintering was performed at a sintering temperature of 1200 ° C. in a vacuum atmosphere of 1 × 10 ⁻² Torr or less. Moreover, in solution treatment step S6, the temperature was lowered to the solution temperature at a temperature drop rate of 1 ° C./min, and the solution treatment was performed under the conditions of a solution temperature of 1170 ° C. for 4 hours. In the rapid cooling step S7, the cooling rate was set to 100 ° C./min. In the aging treatment step S8, the sintered body is heated and held in an inert atmosphere at a temperature of 850 ° C. for 10 hours to perform an isothermal aging treatment, and then a continuous aging treatment is performed to 350 ° C. at a cooling rate of 0.5 ° C./min. And a permanent magnet body was obtained.

  Next, in the product shape processing step S9, the obtained permanent magnet body was cut and processed into the shape of a test piece for measuring the bending compressive strength. The shape of the test piece for measuring the bending compressive strength is a rectangular parallelepiped having a length of 16.2 mm, a width of 12.6 mm, and a height of 0.75 mm, and the easy axis of magnetization is the magnetization direction.

  Finally, in the oxide layer formation heat treatment step S10, the atmospheric conditions were set to the atmosphere, and the heat treatment temperature conditions were set to the heat treatment temperatures shown in Table 1. The number of n in each heat treatment temperature condition was 5.

By passing through the above process, the magnet piece which concerns on Examples 1-5 and Comparative Examples 1-5 was obtained. The obtained magnet piece was magnetized using a pulse magnetizer after heat treatment, and the surface magnetic flux Φm was measured using a flux meter. The measured magnet piece was subjected to a bending compressive strength test, and the three-point bending compressive strength was measured. The measurement results are shown in Table 1.
A good value of the surface magnetic flux Φm [× 10 ⁻⁵ Wb · T] was set to 445 or more, and a good value of the bending compressive strength [N] was set to 50 or more. As shown in Table 1, when the heat treatment temperature is 310 ° C. or higher, the bending compression strength is remarkably improved and reaches a good value. Further, it was observed that when the heat treatment temperature exceeds 510 ° C., the flexural compressive strength is not further improved, and the surface magnetic flux Φm is lowered and does not correspond to a good value. Therefore, when heat-treating in the air, a magnet having good bending compressive strength and small deterioration in magnetic properties was obtained by heat-treating at least within a heat treatment temperature range of 310 ° C to 510 ° C.

(SEM cross-sectional structure observation)
Then, cross-sectional structure | tissue observation was performed about Examples 1-3 and the comparative example 1 using SEM (Scanning Electron Microscope). The photograph by cross-sectional structure | tissue observation is shown to FIGS. FIG. 6 is a photograph showing a microstructure of a cross section in the vicinity of the surface of the permanent magnet of Example 1. FIG. 7 is a photograph showing a microstructure of a cross section in the vicinity of the surface of the permanent magnet of Example 2. FIG. 8 is a photograph showing the microstructure of a cross section near the surface of the permanent magnet of Example 3. FIG. 18 is a photograph showing a cross-sectional microstructure in the vicinity of the surface of the permanent magnet of Comparative Example 1.

  As shown in FIG. 6, in the microstructure cross section of the permanent magnet of Example 1, the base layer 1a, the surface oxide layer 2a, the crack 5a, and the internal oxide layer 6a were observed. The thickness T2a of the surface oxide layer 2a was 50 to 100 nm (= 0.05 to 0.10 μm). The surface oxide layer 2a covers the base layer 1a, and the inner oxide layer 6a fills the crack 5a.

  Note that the protective film P9 shown in FIG. 6 is formed for the purpose of protecting the surface of the permanent magnet of Example 1 in order to perform cross-sectional structure observation. The protective film P9 includes a carbon protective film that is in direct contact with the surface oxide layer 2a and a Pt protective film that covers the carbon protective film. The protective film P9 shown in FIGS. 7, 8, and 18 also has the same configuration.

  Further, as shown in FIG. 7, the base layer 1b, the surface oxide layer 2b, the crack 5b, and the internal oxide layer 6b were also observed in the microstructure cross section of the permanent magnet of Example 2. The thickness T2b of the surface oxide layer 2b was 100 to 200 nm (= 0.10 to 0.20 μm). The surface oxide layer 2b covers the base layer 1b, and the inner oxide layer 6b fills the crack 5b.

  Further, as shown in FIG. 8, the base layer 1c, the surface oxide layer 2c, the crack 5c, and the internal oxide layer 6c were also observed in the microstructure cross section of the permanent magnet of Example 3. The thickness T2c of the surface oxide layer 2c was 200 to 300 nm (= 0.20 to 0.30 μm). The surface oxide layer 2c covers the base layer 1c, and the inner oxide layer 6c fills the crack 5c.

  On the other hand, as shown in FIG. 18, in Comparative Example 1, a base layer 91d and a crack 95d were observed. However, the surface oxide layer covering the base layer 91d and the internal oxide layer filling the crack 95d could not be confirmed. As one of the reasons why the bending compressive strength of Examples 1 to 3 is higher than that of Comparative Example 1, Examples 1 to 3 are different from Comparative Example 1 in that the surface oxide layer and the internal oxide And providing a layer.

(DF-STEM / EDX cross-sectional structure observation)
Next, for the permanent magnet of Example 3, the composition (content) of each element in these cross-sectional structures was determined using DF-STEM / EDX (Dark Field-Scanning Transmission Electron Microscope / Energy Dispersive X-ray Spectroscopy). Measurement and element mapping were performed. FIGS. 9 to 16 show images of these measured cross-sectional structures and element mapping thereof. FIG. 9 is an image obtained by DF-STEM of the permanent magnet of Example 3. 10 to 16 are images obtained by element mapping on the surface of the permanent magnet of Example 3. FIG.

As shown in FIG. 9, in the micro cross-sectional structure near the surface of the permanent magnet of Example 3, a striped layer 3e and a surface oxide layer 2e covering the striped layer 3e were observed. The striped layer 3e shows a striped pattern extending along the boundary surface with the surface oxide layer 2e. The stripe layer 3e has a crack 5e. The crack 5e is filled with the internal oxide layer 6e.
The carbon protective film P92 is a constituent element included in the protective film P9 (see FIG. 6), and is formed for observing the cross-sectional structure.

(Element mapping)
The results of element mapping for C (carbon), O (oxygen), Fe, Co, Cu, Zr, and Sm in the cross section shown in FIG. 9 will be described with reference to FIGS. O (oxygen) and C (carbon) are unavoidable impurities that cannot be avoided in the production. In the images shown in FIGS. 10 to 16, the density indicates the level of the concentration of the element subjected to element mapping, and the lighter the level, the higher the concentration of the element.

  As shown in FIG. 10, the concentration of C (carbon) in the carbon protective film P92 is higher than the concentration of C (carbon) in other parts.

  As shown in FIG. 11, the concentration of O (oxygen) in the crack 5e, the internal oxide layer 6e, and the surface oxide layer 2e is higher than the concentration of O in other portions. In addition, as shown in FIG. 12, Fe has the same tendency as O. That is, the Fe concentration in the crack 5e, the internal oxide layer 6e, and the surface oxide layer 2e is higher than the Fe concentration in other parts.

As shown in FIG. 13, in the crack 5e, the internal oxide layer 6e, and the surface oxide layer 2e, particulate concentrated portions 21a having a high concentration of Co were observed. Further, as shown in FIG. 14, particulate concentrated portions 21b having a high concentration of Cu were observed inside the crack 5e, the internal oxide layer 6e, and the surface oxide layer 2e. A regular lattice pattern of Cu is observed from directly under the surface oxide layer 2e, and it can be seen that a cell structure peculiar to the permanent magnet having the above-described chemical composition is formed in the striped layer 3e. Similar to the base layer 1 (see FIG. 1) of the rare earth cobalt-based permanent magnet 10, the cell structure includes a crystal grain, and the crystal grain includes a cell phase containing Sm ₂ Co ₁₇ . The crystal grains further surround the cell phase and include a cell wall containing SmCo ₅ and a Zr-containing plate phase.

  As shown in FIG. 15, a striped pattern having a high Zr concentration, which is substantially parallel and regular to the sample surface, that is, the surface oxide layer 2e, is observed. This is also a Zr characteristic of a permanent magnet having the above-described chemical composition. It is a rich layer. Referring to FIG. 12 again, a striped pattern with the same orientation as the Zr-rich layer and a wider interval is seen, which matches the striped pattern of the STEM image and the striped pattern of O (oxygen) mapping, It can be seen that the striped pattern is an oxide layer of Fe. As shown in FIG. 16, the striped layer 3e has a higher Sm concentration than other portions, for example, the surface oxide layer 2e, the crack 5e, and the inner oxide layer 6e.

(Chemical composition analysis of each part)
Next, with reference to FIG. 17, the result of each composition analysis of each part in the microstructure of the cross section in the vicinity of the surface of Example 3 will be described. FIG. 17 is a cross-sectional photograph showing the microstructure of the cross section in the vicinity of the surface of Example 3 and each site where the chemical composition was measured.

Table 2 shows the measurement results of the chemical composition analysis at each analysis position shown in FIG.

  As shown in FIG. 17, a base layer 1f, a surface oxide layer 2f, a striped layer 3f, and a transition layer 4f were observed. The base layer 1f, the transition layer 4f, the striped layer 3f, and the surface oxide layer 2f are formed so as to be laminated in this order from the inside to the outside of the rare earth-based cobalt permanent magnet. These transition smoothly from the inside to the outside of the rare earth-based cobalt permanent magnet.

  The surface oxide layer 2f contains Fe, Co, and O as main components. The surface oxide layer 2f includes analysis positions 004 and 005. The analysis results at both analysis locations were very different. At the analysis position 004, the content of Fe and O is high, and at the analysis position 005, the content of Co is high. The surface oxide layer 2f is not made of a compound having a specific chemical composition, and includes, for example, a granular concentrated portion having a high Co content.

  The striped layer 3f includes analysis positions 006, 007, and 012. Striped structures are located at the analysis positions 006 and 007, and stripes, that is, linear portions are located at the analysis position 012. The striped structure includes a linear part and a cell structure, and the linear part and the cell structure constitute a striped pattern indicated by the striped structure. As a result of analysis at the analysis position 012, since the contents of O and Fe are high, the linear portion is considered to be an oxide layer. The analysis results at the analysis positions 006 and 007 are close to the alloy composition and have a lower oxygen concentration than the analysis results at the analysis position 012.

  The transition layer 4f is in contact with the striped layer 3f, a plurality of linear portions extending along the interface with the striped layer 3f, and a cell phase having the same configuration as the cell phase included in the base layer 1f including. The amount of the linear portion included in the transition layer 4f is smaller than the amount of the linear portion included in the striped layer 3f. The transition layer 4f is located between the striped layer 3f and the base layer 1f, and the amount of the linear portion in the transition layer 4f transitions so as to decrease from the striped layer 3f side toward the base layer 1f side. Tend to. Moreover, the space | interval of adjacent linear parts is wide.

  In the base layer 1f, a cell structure having the same configuration as that of the base layer 1 (see FIG. 1) of the rare earth cobalt-based permanent magnet 10 was observed.

  The thickness of the surface oxide layer 2f was about 0.3 μm, the thickness of the striped layer 3f was about 0.7 μm, and the thickness of the transition layer 4f was about 2 μm.

(Examples 6 to 11)
Next, the results of measuring the magnetic characteristics and mechanical strength of Examples 6 to 11 will be described.

Examples 6 to 11 were manufactured using the same manufacturing method as that described above, as in Examples 1 to 5. Specifically, in the raw material blending step S1 (see FIG. 5), the target composition is mass%, Sm: 25.9%, Cu: 4.5%, Fe: 15.0%, Zr: 3.1% The balance was Co. As a mother alloy containing Zr, an Fe 20% Zr 80% alloy was used. Moreover, in ingot casting step S2 and powder production | generation step S3, the same conditions as Examples 1-5 were used. In press molding step S4, press molding was performed using a mold under the conditions of a magnetic field of 15 kOe and a press molding pressure of 1.0 ton / cm ² . In the sintering step S5, sintering was performed at a sintering temperature of 1210 ° C. in a vacuum of 1 × 10 ⁻² Torr or less and an inert atmosphere. Further, in the solution treatment step S6, the temperature was lowered to the solution temperature at a temperature drop rate of 1 ° C./min, and the solution treatment was performed at the solution temperature of 1180 ° C. In the rapid cooling step S7, the cooling rate was set to 100 ° C./min. In the aging treatment step S8, the sintered body is heated and held in an inert atmosphere at a temperature of 800 ° C. for 5 hours to perform an isothermal aging treatment, and then a continuous aging treatment is performed to 350 ° C. at a cooling rate of 1 ° C./min. A permanent magnet body was obtained.

  Next, in the product shape processing step S9, the obtained permanent magnet body was cut using the same manufacturing conditions as in Examples 1 to 5, and processed into the shape of a test piece for measuring the bending compressive strength.

  Finally, in the oxide layer forming heat treatment step S10, the atmospheric conditions were the oxygen partial pressures shown in Table 3, and the heat treatment temperature conditions were the heat treatment temperatures shown in Table 3.

By passing through the above process, the magnet piece which concerns on Examples 6-11 and Comparative Examples 6-9 was obtained. Using the same method as in Examples 1 to 5, the surface magnetic flux Φm and the three-point bending compressive strength were measured. The results are shown in Table 3.

  As shown in Table 3, in Examples 6 to 10, the surface magnetic flux Φm and the bending compressive strength were both good values. In Example 6, although the oxygen partial pressure was 100% in the oxide layer forming heat treatment step S10, the surface magnetic flux Φm and the bending compressive strength were both good values. Therefore, in the oxide layer forming heat treatment step S10, the upper limit value of the oxygen partial pressure is 100%.

On the other hand, in Comparative Example 6, although the surface magnetic flux Φm was a good value (445 × 10 ⁻⁵ Wb · T or more), the bending compressive strength was small and did not correspond to a good value (50 N or more). One possible reason for this is that in Comparative Example 6, there is no oxide layer formation heat treatment step S10, and no oxide layer is formed.

  Further, in Comparative Example 7, although the surface magnetic flux Φm was a good value, the bending compressive strength was small and did not correspond to a good value. One possible reason for this is that in Comparative Example 7, the heat treatment temperature of 180 ° C. in the oxide layer forming heat treatment step S10 is lower than the heat treatment temperature of 200 ° C. in the same step of Example 6. In the oxide layer forming heat treatment step S10, the heat treatment temperature is preferably 200 ° C. or higher.

  Moreover, in the comparative example 8, the bending compressive strength fell and it did not correspond to a favorable value. One reason for this is that in Comparative Example 8, the oxygen partial pressure in the oxide layer forming heat treatment step S10 is 0.8%, which is lower than the oxygen partial pressure in the same step of Example 11 of 1%. . Therefore, in the oxide layer forming heat treatment step S10, the oxygen partial pressure is preferably 1% or more.

  Moreover, in the comparative example 9, the surface magnetic flux (PHI) m fell and it did not correspond to a favorable value. One reason for this is that in Comparative Example 9, the heat treatment temperature in the oxide layer forming heat treatment step S10 is 620 ° C., which is higher than the heat treatment temperature 600 ° C. in the same step of Example 11. Therefore, the heat treatment temperature is preferably 600 ° C. or lower.

  As described above, in the oxide layer forming heat treatment step S10, the oxygen partial pressure is preferably 1% or more and 100% or less, and the heat treatment temperature is preferably in the range of 200 ° C. or more and 600 ° C. or less.

  In addition, although the microstructure cross section of Examples 6-10 was observed, it confirmed that it had the same structure as Examples 1-5.

  The present invention has been described with reference to the above-described embodiment and examples. However, the present invention is not limited only to the configuration of the above-described embodiment and examples, and the scope of the invention of the claims of the claims of this application Of course, various changes, modifications, and combinations that can be made by those skilled in the art are included.

10, 20, 30, 40 Rare earth cobalt-based permanent magnet 1, 1a, 1b, 1c, 1f Base layer 11 Contact surface 2 Surface oxide layer 21, 21a, 21b Concentrated portion 2a, 2b, 2c, 2e, 2f Surface oxide Layer 3, 3e, 3f Stripe layer 31 Linear portion 4, 4f Transition layer 5, 5a, 5b, 5c, 5e Crack 6, 6a, 6b, 6c, 6e Internal oxide layer S9 Product shape processing step S10 Oxide layer Formation heat treatment step

Claims (11)

When the element R is a rare earth element containing at least Sm,
In mass%, R: 23-27%, Cu: 3-6% (excluding 6%), Fe: 10-25%, Zr: 1.5-4.0%, the balance being Co And a rare earth cobalt-based permanent magnet comprising inevitable impurities,
A base layer comprising a first cell phase;
A surface oxide layer covering the base layer,
Rare earth cobalt permanent magnet. The Fe content of the surface oxide layer is higher than the Fe content of the base layer,
The rare earth cobalt-based permanent magnet according to claim 1. The surface oxide layer has a thickness in the range of 50 to 500 nm.
The rare earth cobalt-based permanent magnet according to claim 1 or 2. The base layer comprises a striped layer in contact with the surface oxide layer;
The striped layer includes a plurality of first linear portions extending along an interface with the surface oxide layer.
The rare earth cobalt-based permanent magnet according to any one of claims 1 to 3. The Fe content of the linear portion is higher than the Fe content of the base layer,
The rare earth cobalt-based permanent magnet according to claim 4. Cracks have occurred in the base layer,
The base layer further comprises an inner oxide layer covering the cracks.
The rare earth cobalt-based permanent magnet according to any one of claims 1 to 5, wherein: The inner oxide layer fills the crack;
The rare earth cobalt-based permanent magnet according to claim 6. The base layer comprises a transition layer in contact with the striped layer;
The transition layer includes a plurality of second linear portions extending along the interface with the striped layer, and a second cell phase.
The rare earth cobalt-based permanent magnet according to claim 4, wherein the rare earth cobalt-based permanent magnet is cited. When the element R is a rare earth element containing at least Sm,
In mass%, R: 23-27%, Cu: 3-6% (excluding 6%), Fe: 10-25%, Zr: 1.5-4.0%, the balance being Co And a method for producing a rare earth cobalt based permanent magnet using a permanent magnet body made of inevitable impurities,
A step of forming a surface oxide layer on the permanent magnet body by heating and holding the permanent magnet body at a heat treatment temperature of 200 to 600 ° C. in an atmosphere having an oxygen partial pressure of 1 to 100%.
A method for producing a rare earth cobalt-based permanent magnet. In the step of forming the surface oxide layer on the permanent magnet body,
Holding the permanent magnet body heated in an air atmosphere,
A method for producing a rare earth cobalt-based permanent magnet according to claim 9. In the step of forming the surface oxide layer on the permanent magnet body,
The heat treatment temperature is 300 to 510 ° C.
The method for producing a rare earth cobalt-based permanent magnet according to claim 10.