WO2013061784A1 - R-t-b系合金粉末、並びに異方性ボンド磁石用コンパウンド及び異方性ボンド磁石 - Google Patents
R-t-b系合金粉末、並びに異方性ボンド磁石用コンパウンド及び異方性ボンド磁石 Download PDFInfo
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- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/02—Making ferrous alloys by powder metallurgy
- C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
- C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/054—Nanosized particles
- B22F1/056—Submicron particles having a size above 100 nm up to 300 nm
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0578—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together bonded together
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
- B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
Definitions
- the present invention relates to an RTB-based alloy powder, an anisotropic bonded magnet compound containing the RTB-based alloy powder, and an anisotropic bonded magnet.
- Rare earth magnets made of RTB-based alloys containing rare earth elements are currently known to have the strongest magnetic force.
- Rare earth bonded magnets obtained by kneading and molding the alloy powder with a resin are excellent in the degree of freedom of shape, so that they can be molded relatively easily into a thin shape and are often used for small motors.
- isotropic alloy powders have been mainly used for these applications, but recently, rare earth bonded magnets using anisotropic alloy powders with higher magnetic force have been developed.
- rare earth bonded magnets are rarely used in motors used in high-temperature environments such as automobile engine rooms.
- One reason for this is that the demagnetization at high temperatures is large because the coercive force of the alloy powder used in the rare earth bonded magnet is not sufficiently high. If rare earth bonded magnets can be used even in high-temperature environments of automobiles, it is expected to greatly contribute to energy saving.
- the HDDR method (hydrocracking / dehydrogenation recombination method) is known as a method for producing an RTB-based anisotropic alloy powder for rare earth bonded magnets.
- the HDDR method is a process of sequentially executing hydrogenation, decomposition, dehydrogenation, and recombination.
- the crystal grains are refined to the order of several hundreds of nanometers while maintaining the orientation of the crystal axis of the original raw material alloy, so that an anisotropic alloy powder having a high coercive force can be obtained. Is possible.
- Patent Document 1 proposes to improve the magnetic properties of the alloy powder by changing the reaction rate by controlling the atmosphere during the dehydrogenation recombination process. That is, it is disclosed that the reaction rate of recombination can be controlled by controlling the hydrogen release rate in dehydrogenation, thereby obtaining an alloy powder having a high coercive force.
- the present invention has been made in view of the above circumstances, and by controlling the microstructure of the RTB-based alloy powder, particularly the grain boundary phase that separates the main phase particles, a permanent having high magnetic properties.
- An object of the present invention is to provide an RTB-based alloy powder capable of producing a magnet, an anisotropic bonded magnet compound using the same, and an anisotropic bonded magnet.
- the present invention provides an RTB-based alloy powder (where R is one or more rare earth elements, T is an element composed of at least one of iron and cobalt), and R A main phase particle having an average particle size of 200 nm to 500 nm composed of 2 T 14 B, a grain boundary phase having an R richer composition than the main phase particle, and C, N, O, Al, Si, Ti, V, Cr , Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, W and other additive phases containing at least one of inevitable elements, and the above-mentioned RT
- the ratio of the sum of the perimeters of the grain boundary phase and the sum of the perimeters of the main phase particles in any cross section of the B-based alloy powder is defined as the coverage defined by Equation 1, and the circularity defined by Equation 2 is The coverage of the main phase particles by the grain boundary phase of 0.1 or more and 0.6 or less is 1 Providing an R-T-B type alloy powder, where
- RTB-based alloy powder having the structure of the present invention described above, RTB-based alloy powder having excellent magnetic properties, particularly high coercive force, can be realized.
- the RTB-based alloy powder of the present invention has a composition of RxTyBz (where x, y and z are 28.0 ⁇ x ⁇ 36.0, 62.0 ⁇ y ⁇ 71.0, 1.0 ⁇ alloy satisfying a mass ratio of z ⁇ 1.5), C, N, O, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, It is obtained using a raw material alloy composed of at least one of Sn, Hf, Ta, W and other inevitable elements.
- the circularity is 0.1 or more and 0.6 or less, and 10% or more of the total perimeter of the main phase particles in an arbitrary cross section of the RTB-based alloy powder. It is possible to form the R-rich grain boundary phase sufficient to cover 20% or less.
- the present invention also provides a compound for an anisotropic bonded magnet that includes the RTB-based alloy powder that is anisotropic and a resin.
- the compound for anisotropic bonded magnets of the present invention includes an anisotropic RTB-based alloy powder having excellent magnetic properties, particularly excellent coercive force. Therefore, by using the anisotropic bonded magnet compound of the present invention, an anisotropic bonded magnet having excellent magnetic properties, particularly excellent coercive force can be produced.
- the present invention also provides an anisotropic bonded magnet using the anisotropic RTB-based alloy powder or a compound containing the alloy powder.
- the anisotropic bonded magnet of the present invention includes an anisotropic RTB-based alloy powder having excellent magnetic properties, particularly excellent coercive force, and is obtained by molding in a magnetic field. Therefore, it has a strong magnetic force.
- an RTB-based alloy powder having excellent magnetic properties particularly a high coercive force.
- an anisotropic bonded magnet having excellent magnetic properties, particularly excellent coercive force and residual magnetic flux density, and the anisotropic bonded magnet can provide a compound.
- 3 is a flowchart showing a manufacturing procedure of an RTB-based alloy powder. It is a figure which shows an example of a structure of the reaction furnace used for the HDDR reaction which concerns on this embodiment. 3 is a cross-sectional SEM photograph of an RTB-based alloy powder according to the present embodiment. It is the figure which extracted the main phase particle and the grain boundary phase from the cross-sectional SEM photograph of FIG.
- an embodiment hereinafter referred to as an embodiment
- an example of a method for producing an RTB-based alloy powder according to the present invention will be described in detail with reference to the drawings.
- this invention is not limited by the following embodiment and Example.
- the constituent elements disclosed in the following embodiments and examples include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments and examples may be appropriately combined or may be appropriately selected and used.
- the RTB-based alloy powder according to this embodiment will be described.
- the RTB-based alloy powder according to the present embodiment is an RTB-based alloy powder (where R is one or more rare earth elements, T is at least one of iron and cobalt).
- the ratio of the sum of the perimeters of the grain boundary phase and the sum of the perimeters of the main phase particles is defined as the coverage defined by Formula 1, and is defined by Formula 2.
- the coverage of the main phase particles by the grain boundary phase having a circularity of 0.1 to 0.6 It is characterized by being 10% or more and 40% or less.
- R represents one or more kinds of rare earth elements as described above.
- Rare earth elements refer to Sc, Y, and lanthanoid elements belonging to Group 3 of the long-period periodic table.
- Examples of lanthanoid elements include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. are included.
- the rare earth elements are classified into light rare earth elements and heavy rare earth elements.
- the heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and the light rare earth elements are other rare earth elements.
- R preferably includes Nd from the viewpoint of manufacturing cost and magnetic characteristics.
- T is an element composed of at least one of iron and cobalt as described above.
- the temperature characteristics can be improved without deteriorating the magnetic characteristics.
- B represents boron, but a part thereof may be substituted with C.
- R-T-B type alloy powder in this embodiment is the main phase particles include R 2 T 14 B phase represented by the composition formula of R 2 T 14 B.
- the main phase particles have an average particle size of 200 nm to 500 nm. If the average particle size is less than 200 nm, the magnetization direction of the main phase particles will be in a superparamagnetic state that is randomly reversed by thermal fluctuation, resulting in a decrease in coercive force, and if it exceeds 500 nm, a domain wall will be formed in the main phase particles. This is because there is a problem that the coercive force is lowered due to facilitation.
- the average particle size of the main phase is preferably 220 nm to 400 nm, more preferably 240 nm to 300 nm.
- the RTB-based alloy powder in the present embodiment includes a grain boundary phase having an R-rich composition than the main phase particles.
- the grain boundary phase has a composition in which the content of R is 1.1 times greater than that of the main phase particles.
- the R1.1T4B4 phase may be included.
- the RTB-based alloy powder in the present embodiment further includes C, N, O, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, and Sn. , Hf, Ta, W and an additive phase containing 20% by mass or more of at least one of inevitable elements. It is considered that most of the additive phase segregates between the main phase particles and plays a role of suppressing grain growth of the main phase particles and pinning the domain wall.
- the RTB-based alloy powder in this embodiment has a ratio of the sum of the perimeter of the grain boundary phase and the sum of the perimeter of the main phase particles in an arbitrary cross section of the RTB-based alloy powder.
- the coverage defined by Formula 1 is characterized in that the coverage of the main phase particles by the grain boundary phase having a circularity defined by Formula 2 of 0.1 or more and 0.6 or less is 10% or more and 40% or less. To do.
- ⁇ Formula 1> ⁇ Formula 2>
- the coercive force expression mechanism is not a single-domain particle magnetization rotation type but a domain wall pinning type.
- the domain wall is efficiently pinned to the grain boundary phase. Since it is stopped, a high coercive force can be realized.
- the grain boundary phase having a circularity of less than 0.1 the shape becomes too long and the grain boundary phase becomes thinner than the domain wall thickness, and the domain wall cannot be pinned.
- the domain wall can be pinned only at “points” instead of “lines”, so it does not contribute to the improvement of the coercive force.
- the coverage of the main phase particles by the grain boundary phase having a circularity of 0.1 or more and 0.6 or less exceeds 40 (upper limit)%, the residual magnetic flux density Br is isotropic RT— It will fall to the same level as B alloy. From such a viewpoint, the coverage of the main phase particles by the grain boundary phase having a circularity of 0.1 to 0.6 is more preferably 10% to 40%.
- the grain boundary phase effective as a pinning site has an elongated shape that can pin the domain wall with a “line”. In order to quantitatively represent such a shape, it is expressed by ⁇ Formula 2>. It is best to use circularity.
- the present embodiment is a method for producing an RTB-based alloy powder by performing the HDDR method.
- a raw material starting alloy
- HD Hydrogen Decomposition
- DR Desorption Recombination
- FIG. 1 is a flowchart showing a method for producing an RTB-based alloy powder according to the first embodiment of the present invention. As shown in FIG.
- the method for producing an RTB-based alloy powder according to the present embodiment is a raw material alloy obtained by casting an RTB-based alloy containing an R 2 T 14 B phase to obtain a raw material alloy.
- DR process dehydrogenation recombination process
- DR process for obtaining the rare earth alloy powder (DR process) (step
- an RTB-based raw material alloy containing an R 2 T 14 B phase can be used.
- the raw material alloy has an alloy composition of RxTyBz (where x, y, and z are 28.0 ⁇ x ⁇ 36.0, 62.0 ⁇ It is preferable to use a raw material alloy satisfying a mass ratio of y ⁇ 71.0 and 1.0 ⁇ z ⁇ 1.5.
- R represents at least one rare earth element such as Y, La, Ce, Pr, Nd, Sm, Gd, Td, Dy, Ho, Er, Tm, and Lu.
- T represents one or more transition metal elements including Fe or Fe and Co.
- T may be Fe alone or a part of Fe may be substituted with Co.
- additive elements one of C, N, O, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, W, etc. More than one type may be included.
- the raw material alloy preparation step is a step of obtaining a raw material alloy by casting an RTB-based alloy containing the R 2 T 14 B phase.
- the casting method include an ingot casting method, a strip casting method, a book mold method, and a centrifugal casting method.
- the raw material alloy may contain an inevitable impurity derived from a raw material metal or a raw material compound or a manufacturing process. After preparing the raw material alloy, the process proceeds to the homogenization heat treatment step (step S02).
- the homogenizing heat treatment step is a step of homogenizing the raw material alloy by heating the raw material alloy to near the melting point.
- the raw material alloy is held at a temperature of 1000 ° C. or higher and 1200 ° C. or lower for 5 to 48 hours in a vacuum or an inert gas atmosphere such as Ar gas or N 2 gas. Thereby, the raw material alloy is homogenized.
- the process proceeds to a hydrogen storage process (step S03).
- the present embodiment includes a homogenization heat treatment step (step S02), the present embodiment is not limited to this, and the homogenization heat treatment step (step S02) is performed according to the casting conditions of the raw material alloy. ) May be omitted.
- Step S03 The hydrogen storage step (step S03) is a step of storing hydrogen in the raw material alloy. In the stage of this hydrogen storage step (step S03), only hydrogen is stored in the crystal lattice of the raw material alloy, and the raw material alloy is not decomposed by storing hydrogen.
- the raw material alloy a hydrogen partial pressure in the hydrogen atmosphere with a P 1, is held between a temperature T 1 of the time t 1, hydrogen is occluded in the material alloy.
- the hydrogen partial pressure P 1 is preferably 100 kPa or more and 300 kPa or less.
- Temperatures T 1 is preferably at 100 ° C. or higher 200 ° C. or less.
- Time t 1 is preferably 0.5 hours to 2 hours.
- the hydrogen partial pressure P 1 is less than 100 kPa, the hydrogen in the crystal lattice of the material alloy is not easily absorbed, the hydrogen partial pressure P 1 is exceeds 300 kPa, equipment becomes large scale in terms of explosion-proof.
- the HD process is a process for obtaining a decomposition product by hydrocracking a raw material alloy that has occluded hydrogen.
- the decomposition product obtained by decomposing the raw material alloy by the HD reaction contains a hydride such as RH x and an iron compound such as ⁇ -Fe and Fe 2 B.
- the decomposition product forms a fine matrix of several hundred nm.
- the raw material alloy obtained by absorbing hydrogen in a hydrogen atmosphere of hydrogen partial pressure was set to P 2, held between the high at temperature T 2 time t 2 than the temperature T 1.
- Hydrogen partial pressure P 2 is preferably at 10kPa or 100kPa or less.
- Temperature T 2 is preferably at 850 ° C. or less 700 ° C. or higher.
- the hydrogen partial pressure P 2 is less than 10 kPa, the hydrogenolysis of the raw material alloy may not proceed sufficiently. If the hydrogen partial pressure P 2 exceeds 100 kPa, the rate of hydrocracking is too high, and RT -Anisotropy of B-based alloy powder decreases.
- the hydrogenolysis of the raw material alloy may not proceed sufficiently, and if the temperature T 2 exceeds 850 ° C., it is difficult to obtain a decomposition product (hydride).
- Time t 2 is preferably 10 hours or less than 0.5 hours. If the time t 2 is less than 0.5 hour, the hydrocracking of the raw material alloy may not proceed sufficiently. If the time t 2 exceeds 10 hours, the hydrocracking proceeds too much, and RTB The anisotropy of the alloy powder decreases.
- Step S05> The DR process (steps S05 to 07) is a process in which hydrogen is released from the obtained decomposition product and the decomposition product is recombined to obtain an RTB-based alloy powder.
- the DR process includes a first DR process (step S05), a second DR process (step S06), and a rapid hydrogen exhaust process (step S07).
- the DR process includes three processes, a first DR process, a second DR process, and a rapid hydrogen evacuation process, but the present invention is not limited to this, and the DR process has one stage. It is also possible to perform only four steps or more.
- step S05 First dehydrogenation recombination (DR) step: step S05)
- first DR step (step S05) hydrogen is released for a time t 3 until the hydrogen concentration of the decomposition product reaches ⁇ at the temperature T 3 , and the recombination nuclei of the RTB-based alloy Is a step of generating.
- the hydrogen concentration ⁇ of the decomposition product in the first DR process (step S05) is 0.28% by mass to 0.30% by mass in order to more uniformly generate nuclei of the RTB-based alloy. Is preferred.
- the first DR temperature T 3 of the decomposition product in the first DR step (step S05) is preferably 750 ° C. or higher and 950 ° C. or lower, and more preferably 800 ° C. or higher and 900 ° C. or lower.
- the first DR temperature T 3 is less than 750 ° C., the release rate of hydrogen from the decomposition product cannot be increased sufficiently, and hydrogen remains. On the other hand, when the first DR temperature T 3 is higher than 950 ° C., it tends to occur abnormal grain growth of the rare earth alloy powder.
- the time t 3 of the first DR step (step S05) is preferably 0.05 hours to 0.2 hours, for example, but the time t 3 is appropriately adjusted according to the release rate of hydrogen from the decomposition product.
- step S06 Silicon dehydrogenation recombination (DR) step: step S06)
- the hydrogen release rate from the decomposition product is made lower than that in the first DR process (step S05).
- hydrogen is further released from the decomposition products, and the decomposition products are slowly recombined to grow crystal grains of the RTB-based alloy.
- Temperature T 4 of the second DR process is preferably the same as the temperature T 3 in the first DR process (step S05). Thereby, the release of hydrogen from the decomposition product can proceed smoothly.
- the hydrogen release rate in the second DR step (step S06) is 1/10 to 1/100 of the hydrogen release rate in the first DR step (step 07).
- FIG. 2 is a diagram illustrating an example of a configuration of a reaction furnace used for the HDDR reaction.
- the reaction furnace 10 includes a furnace body 11, a processing container 12, a heater 13, a heat insulating material 14, thermometers 15 and 16, and a temperature measuring device 17.
- the reactor 10 has a gas inlet 21 and a gas outlet 22 on the wall surface.
- inert gas or H 2 gas is supplied into the furnace body 11 from the gas inlet 21. Examples of the inert gas include Ar gas and N 2 gas.
- the reactor 10 extracts the gas in the furnace body 11 from the gas exhaust port 22 so that the pressure can be controlled.
- the furnace body 11 has a hearth 23 inside thereof, and the processing vessel 12 is provided on the hearth 23.
- the furnace body 11 is provided with a heater 13 on its outer periphery.
- the outer periphery of the heater 13 is covered with a heat insulating material 14.
- the thermometer 15 is provided by being inserted into the decomposition product S accommodated in the processing container 12.
- the thermometer 16 is provided in a space inside the furnace body 11.
- the thermometers 15 and 16 are each connected to a temperature measuring device 17.
- the temperature measuring device 17 measures the temperature of the decomposition product S with the thermometer 15 and measures the temperature in the space inside the furnace body 11 with the thermometer 16.
- the temperature of the decomposition product S measured by the thermometer 15 is set as a sample temperature T1
- the atmosphere temperature in the furnace of the furnace body 11 measured by the thermometer 16 is set as an atmosphere temperature T2.
- the sample temperature T1 is maintained at a constant state around 850 ° C.
- the atmospheric temperature T2 is confirmed to have a peak point (hereinafter referred to as “peak point A”).
- This peak point A can be said to be a temperature change of the atmospheric temperature T2 caused by an increase in the heater output of the furnace due to the completion of the recombination reaction of the DR reaction.
- the DR hydride (RH 2 ) contained in the raw material alloy undergoes a DR reaction as represented by the following formula (1).
- a dehydrogenation reaction (the following formula (2)) that is an endothermic reaction and a recombination reaction (the following formula (3)) that is an exothermic reaction proceed in detail.
- the DR reaction of the following formula (1) is an endothermic reaction as a whole, and Q1 of the following formula (1) is represented by the difference between Q2 of the following formula (2) and Q3 of the following formula (3).
- Time t 4 of the second DR process (step S06) is, for example, preferably 5 hours 0.5 hours, the time t 4 is appropriately adjusted according to the rate of release of hydrogen from the cracked products.
- Rapid hydrogen evacuation step (step S07) is conducted at a temperature T 5, during the time t 5, and P 5 under reduced pressure to hydrogen partial pressure, thereby once releasing hydrogen remaining in the R-T-B type alloy process It is.
- T 5 is preferably the same as T 4 .
- Time t 5 is good the shorter, it is desirable that furnace hydrogen partial pressure within at least 5 minutes to reach the P 5.
- P 5 is preferably less than 100 Pa.
- at the end point of the recombination reaction in the second DR process (step S06), and increases the drop rate of hydrogen partial pressure P 4.
- a dehydrogenation reaction and a recombination reaction occur.
- the recombination reaction is completed, main phase particles and grain boundary phases are formed in the RTB-based alloy powder. Since the temperature T 4 is about 850 ° C., the grain boundary phase has a liquid phase. If the rate of decrease in the hydrogen partial pressure is left as it is in the second DR process, it takes a considerable time to complete the dehydrogenation reaction. Pooling is important, and the degree of circularity is close to 1. Therefore, at the time when the recombination reaction in the DR step is completed, the rate of decrease in the hydrogen partial pressure is increased at a stretch, and the dehydrogenation reaction is terminated early.
- Step S09 is a step of cooling the RTB-based alloy powder obtained by the HDDR reaction to room temperature with an inert gas for cooling.
- an inert gas for cooling.
- Ar gas or N 2 gas is used as the inert gas.
- the supply of the inert gas is stopped to obtain a rare earth alloy powder.
- the RTB-based alloy powder produced by the above process has a high coercive force HcJ.
- the obtained RTB-based alloy powder can be further pulverized to prepare an RTB-based alloy powder in a powder form of 50 ⁇ m to 300 ⁇ m or less.
- the RTB-based alloy powder is preferably pulverized using a pulverizing means such as a stamp mill or a jaw crusher and then sieved.
- the grain boundary phase is prevented from pooling to the triple point, and the circularity is 0.1 or more and 0. Since a grain boundary phase of .6 or less is formed, an RTB-based alloy powder having a high coercive force HcJ can be realized using the HDDR method.
- This RTB-based alloy powder can be suitably used as a magnet powder for an anisotropic bonded magnet, and a permanent magnet having a high coercive force HcJ can be produced.
- the coverage of the main phase particles by the grain boundary phase having a circularity of 0.1 to 0.6 can be controlled, for example, by changing the composition of the rare earth element of the raw material alloy.
- the grain boundary phase having a circularity of 0.1 or more and 0.6 or less causes 10% or more and 40% or less of the total perimeter of the main phase particles. Covered. If the composition of the rare earth element of the raw material alloy is less than 28.0% by mass, a sufficient amount of grain boundary phase cannot be formed to cover at least 10% of the surface area of the main phase particles, and the high coercive force is high. I can't get it.
- composition of the rare earth element of the raw material alloy exceeds 36.0% by mass, more than 40% of the surface area of the main phase particles is easily covered with the grain boundary phase. Even if the coverage of the grain boundary phase is increased as such, As a result, the magnetic force of the RTB-based alloy powder is reduced.
- the coverage of the main phase particles by the grain boundary phase having a circularity of 0.1 or more and 0.6 or less can also be controlled by the process conditions of the HDDR reaction. For example, increasing the temperature T 2 of the HD process (step S04), it is possible to increase the coverage of the grain boundary phase.
- the RTB-based alloy powder of the present embodiment is manufactured by the HDDR method, but the present invention is not limited to this.
- the RTB system An RTB-based alloy powder in which, in an arbitrary cross section of the alloy powder, 10% or more and 40% or less of the total circumference of the main phase particle is coated with a grain boundary phase having a circularity of 0.1 to 0.6 Can be manufactured.
- the RTB-based alloy powder of this embodiment has a high coercive force HcJ, it can be used even at high temperatures. Therefore, it can be suitably used as an RTB-based alloy powder for magnets used in high-temperature environments such as automobile engine rooms.
- a rare earth bonded magnet is a magnet obtained by molding a compound (composition) for a rare earth bonded magnet obtained by kneading a resin binder containing a resin and magnet powder into a predetermined shape.
- Rare earth bonded magnets can be isotropic and anisotropic when molded.
- An isotropic rare earth bonded magnet is obtained by molding a compound for a rare earth bonded magnet containing an RTB-based alloy powder without applying a magnetic field during molding.
- An anisotropic rare earth bonded magnet is obtained by applying a magnetic field during molding to orient the crystal axes of the RTB-based alloy powder contained in the compound in a certain direction.
- a resin binder containing a resin and an RTB-based alloy powder are kneaded by a pressure kneader such as a pressure kneader to prepare a rare earth bonded magnet compound (composition).
- the resin include thermosetting resins such as epoxy resins and phenol resins, styrene-based, olefin-based, urethane-based, polyester-based, polyamide-based elastomers, ionomers, ethylene-propylene copolymers (EPM), and ethylene-ethyl acrylate.
- thermoplastic resins such as polymers and polyphenylene sulfide (PPS).
- the resin used for compression molding is preferably a thermosetting resin, and more preferably an epoxy resin or a phenol resin.
- the resin used for injection molding is preferably a thermoplastic resin.
- the content ratio of the RTB-based alloy powder and the resin in the rare earth bonded magnet is, for example, 0.5% by mass or more and 20% by mass or less of the resin with respect to 100% by mass of the RTB-based alloy powder. It is preferable to include.
- the resin content is less than 0.5% by mass relative to 100% by mass of the rare earth alloy powder, the shape retention tends to be impaired, and when the resin exceeds 20% by mass, sufficiently excellent magnetic properties are obtained. Tends to be difficult to obtain.
- the rare earth bonded magnet containing the RTB-based alloy powder and the resin can be obtained by injection molding the rare earth bonded magnet compound.
- the rare earth bonded magnet compound is heated to the melting temperature of the binder (thermoplastic resin) as necessary to obtain a fluid state, and then the rare earth bonded magnet compound is Molding is performed by injection into a mold having a shape. Then, it cools and takes out the molded article (rare earth bond magnet) which has a predetermined shape from a metal mold
- the manufacturing method of the rare earth bonded magnet is not limited to the above-described method by injection molding.
- the rare earth bonded magnet containing RTB alloy powder and resin by compression molding a compound for rare earth bonded magnet. May be obtained.
- the rare earth bonded magnet compound is filled into a mold having a predetermined shape, and pressure is applied to A molded product (rare earth bonded magnet) having a predetermined shape is taken out.
- the compression molding machine such as a mechanical press or a hydraulic press is used.
- the resin is cured by putting it in a furnace such as a heating furnace or a vacuum drying furnace to obtain a rare earth bonded magnet.
- the shape of the rare earth bonded magnet obtained by molding is not particularly limited, and may be changed according to the shape of the rare earth bonded magnet, such as a flat plate shape, a column shape, or a ring shape, depending on the shape of the mold to be used. it can. Further, the obtained rare earth bonded magnet may be plated or painted on the surface in order to prevent the deterioration of the oxide layer, the resin layer and the like.
- the RTB-based alloy powder of the present embodiment suppresses the pooling of the grain boundary phase at the triple point, and the grain boundary phase having a circularity of 0.1 to 0.6 is formed. High coercivity HcJ. For this reason, the rare earth bonded magnet obtained using this RTB-based alloy powder can have a high coercive force HcJ.
- a magnetic field may be applied to orient the crystal axis of the RTB-based alloy powder in a certain direction.
- Example 1 An Nd—Fe—B raw material alloy having the following composition was prepared by a strip casting method.
- This raw material alloy contained a small amount of inevitable impurities (0.1 to 0.3% by mass of the whole raw material alloy) in addition to the above-described elements.
- This raw material alloy was kept in a temperature range of 1000 to 1200 ° C. for 24 hours in a vacuum (homogenization heat treatment step).
- the homogenized heat-treated Nd—Fe—B raw material alloy was pulverized using a stamp mill and sieved to obtain a granular raw material alloy (particle diameter of 1 to 2 mm).
- the raw material alloy was filled in a molybdenum-made container, loaded into a tubular heat treatment furnace having an infrared heating method, and subjected to a treatment by hydrocracking / dehydrogenation recombination (HDDR treatment) under the following conditions.
- the flowchart of the processing is as shown in FIG.
- hydrogen gas is introduced into a tubular heat treatment furnace, and a hydrogen occlusion process (S03 in FIG. 1) in which the raw material alloy powder is held for 2 hours under the hydrogen gas atmosphere under the conditions of hydrogen partial pressure of 100 kPa and temperature (T 1 ) of 100 ° C. ) As a result, hydrogen was occluded in the raw material alloy.
- the decomposition product was reduced to a hydrogen concentration ⁇ (0.28% by mass) based on the mass of the entire decomposition product before releasing hydrogen.
- the time required for the first DR process was 4 minutes.
- FIG. 2 is a diagram showing the configuration of the reactor used for the HDDR reaction.
- the thermometer 15 measures the sample temperature T1
- the thermometer 16 measures the atmospheric temperature T2 in the furnace.
- the sample temperature T1 is controlled to be constant at a temperature corresponding to each step during the HDDR reaction.
- the valve provided at the gas exhaust port is fully opened to increase the hydrogen release rate.
- the time required for the furnace pressure to reach less than 100 Pa was about 5 minutes.
- the obtained Nd—Fe—B alloy powder was pulverized using a mortar in an inert atmosphere and sieved to obtain an Nd—Fe—B alloy powder having a particle size of 53 to 212 ⁇ m.
- the powder and paraffin were packed in a case, and a magnetic field of 1 Tesla was applied with the paraffin melted to orient the Nd—Fe—B alloy powder.
- a magnetic field of 6 Tesla was applied in a direction parallel to the orientation direction of the alloy powder, and the magnetization-magnetic field curve was measured using a vibrating sample magnetometer (VSM) to obtain the magnetic characteristics.
- the measurement result of the coercive force (Hcj) was 19.3 kOe.
- FIG. 3 shows the result of observing the structure of the main phase particles and the grain boundary phase of the Nd—Fe—B alloy powder using the reflected electron image of FE-SEM using this observation sample. Since the part that appears gray is the main phase and the part that appears white is the grain boundary phase, the part is extracted and converted into a black-and-white image as shown in FIG. The perimeter of the cross section and the circularity of the cross section of the grain boundary phase were evaluated.
- the shape and distribution of the main phase particles and grain boundary phases vary somewhat depending on the Nd—Fe—B powder, and the shape of the main phase particles and grain boundary phases that are actually three-dimensional is 2 Since evaluation is performed using a three-dimensional image, it is necessary to observe and evaluate as many main phase particles and grain boundary phases as possible. Accordingly, reflected electron images (including approximately 100 or more main phase particles) having a field of view of approximately 3 ⁇ m ⁇ 4 ⁇ m were photographed at five different locations, and an average value thereof was obtained.
- the coverage defined by Equation 1 is the ratio of the total perimeter of the cross section of the grain boundary phase having a circularity of 0.1 to 0.6 and the total perimeter of the cross section of the main phase particle. Was calculated to be 17.5%. Similarly, the result of calculating the coverage by the grain boundary phase having a circularity of less than 0.1 or exceeding 0.6 was 12.1%.
- Example 2 An Nd—Fe—B alloy powder was obtained in the same manner as in Example 1 except that the composition of the raw material alloy was as shown below.
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 12.2%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or more than 0.6 was 12.3%.
- the coercive force of this Nd—Fe—B powder was 17.9 kOe.
- Example 3 An Nd—Fe—B alloy powder was obtained in the same manner as in Example 1 except that the composition of the raw material alloy was as shown below.
- Nd 28.1% by mass Fe: 64.9 mass% Co: 5.0% by mass B: 1.1% by mass Ga: 0.4 mass% Nb: 0.3% by mass
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 10.1%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or more than 0.6 was 12.1%.
- the coercive force of this Nd—Fe—B powder was 16.7 kOe.
- Example 4 An Nd—Fe—B alloy powder was obtained in the same manner as in Example 1 except that the composition of the raw material alloy was as shown below.
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 21.5%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or exceeding 0.6 was 12.0%.
- the coercive force of this Nd—Fe—B powder was 20.5 kOe.
- Example 5 Nd—Fe—B alloy powder was obtained in the same manner as in Example 1, except that the time required from the end of the recombination reaction to the start of cooling was 0.5 minutes.
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 26.7%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or exceeding 0.6 was 9.8%.
- the coercive force of this Nd—Fe—B powder was 21.2 kOe.
- Example 6 Nd—Fe—B alloy powder was obtained in the same manner as in Example 4 except that the time required from the completion of the recombination reaction to the start of cooling was 0.5 minutes.
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 32.3%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or more than 0.6 was 9.6%.
- the coercive force of this Nd—Fe—B powder was 23.5 kOe.
- Example 7 An Nd—Fe—B alloy powder was obtained in the same manner as in Example 6 except that the composition of the raw material alloy was as shown below.
- Nd 35.5% by mass Fe: 57.2 mass% Co: 5.0% by mass B: 1.5% by mass Ga: 0.4 mass% Nb: 0.3% by mass
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 37.4%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or more than 0.6 was 9.5%.
- the coercive force of this Nd—Fe—B powder was 25.2 kOe.
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 8.0%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or more than 0.6 was 15.8%.
- the coercive force of this Nd—Fe—B powder was 16.1 kOe.
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 6.9%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or more than 0.6 was 22.7%.
- the coercive force of this Nd—Fe—B powder was 15.6 kOe.
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 7.4%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or more than 0.6 was 27.5%.
- the coercive force of this Nd—Fe—B powder was 15.9 kOe.
- Nd 37.9% by mass Fe: 54.6 mass% Co: 5.0% by mass B: 1.6% by mass Ga: 0.4 mass% Nb: 0.3% by mass
- the ratio of the main phase particles covered with the grain boundary phase having a circularity of 0.1 to 0.6 was 42.1%. Further, the coverage by the grain boundary phase having a circularity of less than 0.1 or exceeding 0.6 was 10.5%.
- the coercive force of this Nd—Fe—B powder was 27.7 kOe.
- the Nd ⁇ produced using the HDDR method was provided with a quick exhaust process in which the time required for the start of cooling within 5 minutes after completion of the recombination reaction in the second DR process (step S06).
- the Fe—B alloy powder (Example 2 or Example 4) was made of an Nd—Fe—B alloy powder (Comparative Example 1, Compared with Comparative Example 2 or Comparative Example 3), the coverage by the grain boundary phase having a circularity of 0.1 or more and 0.6 or less was high (in Example 2, it was 12.2%, whereas in Comparative Example 2) 1 was 8.0%, Comparative Example 2 was 6.9%, or Example 4 was 21.5%, while Comparative Example 3 was 7.4%).
- Comparative Example 1 it was 17.9 kOe
- Comparative Example 1 The 16.1KOe, in Comparative Example 2 15.6KOe or, whereas was 20.5kOe in Example 4, 15.9KOe Comparative Example 3).
- the Nd—Fe—B alloy powder produced by providing a quick exhaust process in which the time required for starting cooling is within 5 minutes after completion of the recombination reaction in the second DR process (step S06) using the HDDR method.
- the Nd composition is small (Example 3)
- Example 3 the grain boundary phase having a circularity of 0.1 or more and 0.6 or less as compared with the case where the Nd composition is large (for example, Example 1).
- Example 1 the grain boundary phase having a circularity of 0.1 or more and 0.6 or less as compared with the case where the Nd composition is large (for example, Example 1).
- the coercive force was reduced (in Example 1). It was 19.3 kOe, compared with 16.7 kOe in Example 3.
- step S07 when the RTB-based alloy powder is produced by the HDDR method, a rapid hydrogen exhausting step is provided after the completion of the recombination reaction in the second DR step (step S07). It has been found that the coverage by the grain boundary phase of 6 or less can be improved and the coercive force HcJ can be increased.
- the anisotropic bonded magnets produced using the Nd—Fe—B alloy powders obtained in the examples have a low demagnetization factor and very high heat resistance at high temperatures.
- Comparative Example 4 in which the coverage of the main phase particles by the grain boundary phase having a circularity of 0.1 or more and 0.6 or less exceeds 40% the residual magnetic flux density Br is isotropic although the demagnetization factor is low. It became lower than the bond magnet, and it was found that it was not put to practical use.
- the RTB-based alloy powder according to the present invention is useful for producing a rare earth bonded magnet exhibiting a high coercive force HcJ, and can be suitably used as a permanent magnet.
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Abstract
Description
希土類元素を含有するR-T-B系合金からなる希土類磁石は、現在最も強い磁力が得られることで知られている。その合金粉末を樹脂と混練・成形した希土類ボンド磁石は、形状自由度にも優れていることから薄肉形状にも比較的容易に成形でき、小型のモーターに多く使用されている。これまで、これらの用途には主に等方性の合金粉末が使用されてきたが、最近は異方性の合金粉末を使用した、より磁力の強い希土類ボンド磁石も開発が進んできている。
しかしながら、現状では自動車のエンジンルームなどの高温環境下で使用されるモーターには、希土類ボンド磁石はほとんど使われていない。この理由のひとつは、希土類ボンド磁石に使われる合金粉末の保磁力が十分に高くないため、高温での減磁が大きいためである。自動車の高温環境下でも希土類ボンド磁石が使用できるようになれば、省エネに大きく貢献するものと期待される。
<式1>
<式2>
本実施形態に係るR-T-B系の合金粉末について説明する。本実施形態に係るR-T-B系の合金粉末は、R-T-B系合金粉末であって(ただし、Rは一種類以上の希土類元素、Tは鉄、コバルトの少なくとも一種以上からなる元素)、R2T14Bからなる平均粒径200nm以上500nm以下の主相粒子と、前記主相粒子よりもRリッチな組成の粒界相と、C、N、O、Al、Si、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Zr、Nb、Mo、In、Sn、Hf、Ta、Wおよびその他不可避元素の少なくとも一種類以上を含む添加物相から構成されており、前記R-T-B系合金粉末の任意の断面において、粒界相の周囲長の和と主相粒子の周囲長の和との比率を式1で定義する被覆率とし、式2で定義される円形度が0.1以上0.6以下の粒界相による主相粒子の被覆率が10%以上40%以下であることを特徴とする。
<式1>
<式2>
<式1>
<式2>
主相粒子の平均粒径が200nm以上500nm以下の場合、保磁力の発現機構は完全な単磁区粒子の磁化回転型ではなく、磁壁ピンニング型が混在しているものと考えられる。円形度が0.1以上0.6以下の細長い形状をした粒界相によ主相粒子の被覆率が10%以上である構造とすることによって、磁壁が前記粒界相に効率的にピン止めされるため、高い保磁力を実現することが可能となる。円形度が0.1未満の粒界相では、形状が細長くなりすぎるために、磁壁厚さよりも粒界相が薄くなってしまい、磁壁をピン止めすることができない。逆に、円形度が0.6を越える粒界相では、形状が球に近くなるので、磁壁を「線」ではなく「点」でしかピン止めできないため、保磁力の向上に寄与しない。また、円形度が0.1以上0.6以下の粒界相による主相粒子の被覆率が、40(上限)%を超えてしまうと、残留磁束密度Brが等方性のR-T-B合金と同程度まで低下してしまう。このような観点から、円形度が0.1以上0.6以下の粒界相による主相粒子の被覆率は、10%以上40%以下であることがより好ましい。磁壁のピン止めサイトとしての前記粒界相の分布状態を定量的に評価するためには、前記主相粒子1個当たりに対して前記粒界相がどの程度存在しているのかを表す必要があるので、<式1>で表される被覆率を使うのが最も適している。また、<式1>で表される被覆率と保磁力との関係を正しく求めるためには、前期粒界相の中で磁壁のピン止めサイトとして有効に機能するもののみをカウントする必要がある。ピン止めサイトとして有効な前記粒界相は、磁壁を「線」でピン止めできる細長い形状をしたものであり、そのような形状を定量的に表すためには、<式2>で表される円形度を使用するのが最も適している。
前記組成の原料合金を用いることにより、円形度が0.1以上0.6以下の前記粒界相で、前記R-T-B系合金粉末の任意の断面において、前記主相粒子の全周囲長の10%以上40%以下を被覆するのに十分な量のRリッチな前記粒界相を形成することが可能となる。
原料合金準備工程(ステップS01)は、R2T14B相を含むR-T-B系合金を鋳造して原料合金を得る工程である。鋳造方法は、例えばインゴット鋳造法やストリップキャスト法やブックモールド法や遠心鋳造法などである。原料合金は、原料金属又は原料化合物や製造工程に由来する不可避な不純物を含んでいてもよい。原料合金を準備した後、均質化熱処理工程(ステップS02)に移行する。
均質化熱処理工程(ステップS02)は、原料合金を融点近傍まで加熱して原料合金を均質化させる工程である。原料合金を真空又はArガスやN2ガスなどの不活性ガス雰囲気中、1000℃以上1200℃以下の温度で5時間から48時間保持する。これにより、原料合金は均質化される。原料合金が均質化された後、水素吸蔵工程(ステップS03)に移行する。なお、本実施形態では、均質化熱処理工程(ステップS02)を含んでいるが本実施形態はこれに限定されるものではなく、原料合金の鋳造条件などに応じて、均質化熱処理工程(ステップS02)は省略してもよい。
水素吸蔵工程(ステップS03)は、原料合金に水素を吸蔵させる工程である。この水素吸蔵工程(ステップS03)の段階では、原料合金の結晶格子中に水素が吸蔵されているだけで、原料合金は水素を吸蔵したことによって分解していない。水素吸蔵工程(ステップS03)では、原料合金は水素分圧をP1とした水素雰囲気中に、温度T1で時間t1の間保持され、水素が原料合金に吸蔵される。水素分圧P1は、100kPa以上300kPa以下であることが好ましい。温度T1は、100℃以上200℃以下であることが好ましい。時間t1は、0.5時間から2時間であることが好ましい。水素分圧P1と温度T1と時間t1とを上記範囲内とすることで、原料合金はその結晶格子中に水素を吸蔵することができる。
HD工程(ステップS04)は、水素を吸蔵させた原料合金を水素化分解させて分解生成物を得る工程である。原料合金がHD反応で分解して得られる分解生成物は、RHxなどの水素化物、α-Fe及びFe2Bなどの鉄化合物を含んでいる。分解生成物は、数百nmの微細なマトリックスを形成している。HD工程(ステップS04)では、水素を吸蔵させた原料合金を、水素分圧をP2とした水素雰囲気中、温度T1よりも高い温度T2で時間t2の間保持する。
DR工程(ステップS05から07)は、得られた分解生成物から水素を放出させ、分解生成物を再結合させ、R-T-B系合金粉末を得る工程である。本実施形態では、DR工程は、第1のDR工程(ステップS05)と第2のDR工程(ステップS06)と急速水素排気工程(ステップS07)を含む。本実施形態では、DR工程は、第1のDR工程と第2のDR工程と急速水素排気工程の3つの工程からなるが、本発明はこれに限定されるものではなく、DR工程は1段階のみでもよく、4段階以上行なうようにしてもよい。
第1のDR工程(ステップS05)は、温度T3で、分解生成物の水素濃度がηになるまで、時間t3の間、水素を放出させ、R-T-B系合金の再結合核を生成させる工程である。
第2のDR工程(ステップS06)は、第2のDR温度T4で、時間t4の間、第1のDR工程(ステップS05)よりも分解生成物からの水素の放出速度を小さくして分解生成物から更に水素を放出させ、分解生成物を緩やかに再結合させてR-T-B系合金の結晶粒を成長させる工程である。
RH2 + 6Fe + 1/2Fe2B → 1/2R2Fe14B+ H2 -Q1 ・・・(1)
RH2 → R + H2 -Q2 ・・・(2)
R + 6Fe + 1/2Fe2B → 1/2R2Fe14B +Q3 ・・・(3)
急速水素排気工程(ステップS07)は、温度T5で、時間t5の間、水素分圧を減圧してP5とし、R-T-B系合金に残存している水素を一気に放出させる工程である。T5はT4と同じにすることが好ましい。時間t5は短ければ短いほど良いが、少なくとも5分以内に炉内水素分圧がP5に到達することが望ましい。P5は100Pa未満にすることが好ましい。 本実施形態では、第2のDR工程(ステップS06)における再結合反応の終了点で、水素分圧P4の降下速度を上昇させている。
冷却工程(ステップS09)は、冷却用の不活性ガスによりHDDR反応で得られたR-T-B系合金粉末を室温にまで冷却する工程である。不活性ガスとしては、例えば、Arガス、N2ガスなどが用いられる。不活性ガスによりHDDR反応で得られた希土類合金粉末を室温まで冷却した後、前記不活性ガスの供給を停止し、希土類合金粉末を得る。以上の工程により製造されるR-T-B系合金粉末は高い保磁力HcJを有する。
このR-T-B系合金粉末は、異方性ボンド磁石用の磁石粉末として好適に用いることができ、高い保磁力HcJを有する永久磁石を製造することが可能となる。
希土類ボンド磁石は樹脂を含む樹脂バインダーと磁石粉末とを混練して得られる希土類ボンド磁石用コンパウンド(組成物)を所定の形状に成形して得られる磁石である。希土類ボンド磁石は、成形する際、等方性、異方性とすることができる。等方性希土類ボンド磁石は成形する際、磁場を印加しないでR-T-B系合金粉末を含む希土類ボンド磁石用コンパウンドを成形することにより得られる。異方性希土類ボンド磁石は成形する際、磁場を印加して前記コンパウンドに含まれるR-T-B系合金粉末の結晶軸を一定方向に配向させることにより得られる。
ストリップキャスト法によって、以下の組成を有するNd-Fe-B原料合金を調製した。
Fe:61.1質量%
Co:5.0質量%
B:1.3質量%
Ga:0.4質量%
Nb:0.3質量%
得られたNd-Fe-B合金粉末を、不活性雰囲気中で乳鉢を用いて粉砕し、篩い分けを行って、粒径が53~212μmのNd-Fe-B合金粉末とした。この粉末とパラフィンとをケースに詰めて、パラフィンを融解させた状態で1テスラの磁場を印加してNd-Fe-B合金粉末を配向させた。合金粉末の配向方向と平行な方向に6テスラのパルス磁場を印加し、振動試料型磁力計(VSM)を用いて磁化-磁場曲線を測定して磁気特性を求めた。保磁力(Hcj)の測定結果は19.3kOeであった。
上記工程で得られたNd-Fe-B合金粉末をエポキシ樹脂に埋め込んで研磨し、微細構造観察用サンプルを作製した。この観察用サンプルを用い、Nd-Fe-B合金粉末の主相粒子および粒界相の構造をFE-SEMの反射電子像を用いて観察した結果を図3に示す。 グレーに見えている部分が主相、白く見えている部分が粒界相であるため、その部分を抽出して図4のような白黒画像化した上で、画像解析ソフトウェアにて、主相粒子の断面の周囲長、粒界相の断面の円形度を評価した。主相粒子や粒界相の形状・分布状態には、各々のNd-Fe-B粉末毎によって多少のバラツキがある上、実際には3次元である主相粒子や粒界相の形状を2次元の像で評価しているため、なるべく多くの主相粒子、粒界相を観察・評価する必要がある。そこで、およそ3μm×4μmの視野の反射電子像(およそ100個以上の主相粒子が含まれる)を5箇所の異なる場所で撮影し、それらの平均値を求めた。
前記円形度0.1以上0.6以下の粒界相の断面の周囲長の合計と、前記主相粒子の断面の周囲長の合計との比率を取って、式1で定義される被覆率を計算した結果、17.5%であった。また、同様にして円形度が0.1未満又は0.6を越える粒界相による被覆率を計算した結果は、12.1%であった。
<式1>
原料合金の組成が下記に示すものであること以外は、実施例1と同様の方法で、Nd-Fe-B合金粉末を得た。
Fe:63.1質量%
Co:5.0質量%
B:1.2質量%
Ga:0.4質量%
Nb:0.3質量%
原料合金の組成が下記に示すものであること以外は、実施例1と同様の方法で、Nd-Fe-B合金粉末を得た。
Fe:64.9質量%
Co:5.0質量%
B:1.1質量%
Ga:0.4質量%
Nb:0.3質量%
原料合金の組成が下記に示すものであること以外は、実施例1と同様の方法で、Nd-Fe-B合金粉末を得た。
Fe:59.0質量%
Co:5.0質量%
B:1.4質量%
Ga:0.3質量%
再結合反応終了後から冷却開始までの所要時間が0.5分間であること以外は、実施例1と同様の方法で、Nd-Fe-B合金粉末を得た。
再結合反応終了後から冷却開始までの所要時間が0.5分間であること以外は、実施例4と同様の方法で、Nd-Fe-B合金粉末を得た。
原料合金の組成が下記に示すものであること以外は、実施例6と同様の方法で、Nd-Fe-B合金粉末を得た。
Fe:57.2質量%
Co:5.0質量%
B:1.5質量%
Ga:0.4質量%
Nb:0.3質量%
再結合反応終了後から冷却開始までの所要時間が10分間であること以外は、実施例2と同様の方法で、Nd-Fe-B合金粉末を得た。
再結合反応終了後から冷却開始までの所要時間が40分間であること以外は、実施例2と同様の方法で、Nd-Fe-B合金粉末を得た。
再結合反応終了後から冷却開始までの所要時間が60分間であること以外は、実施例4と同様の方法で、Nd-Fe-B粉末を得た。
原料合金の組成が下記に示すものであること以外は、実施例6と同様の方法で、Nd-Fe-B合金粉末を得た。
Fe:54.6質量%
Co:5.0質量%
B:1.6質量%
Ga:0.4質量%
Nb:0.3質量%
実施例1、実施例7、比較例4(被覆率オーバー)にて得られたNd-Fe-B合金粉末をポリフェニレンサルファイド樹脂と混練して希土類ボンド磁石用コンパウンドを作製し、330℃に加熱した状態でφ10×7の円柱形状を有する金型内に射出して成形を行った。射出成形時には約1.5テスラの磁場を円柱の高さ方向に印加して、Nd-Fe-B合金粉末を配向させた。このようにして作製した異方性希土類ボンド磁石を着磁して、フラックスメーターにて磁力を測定した後、恒温槽内にて150℃で1000時間放置し、再度磁力を測定して減磁率を求めた結果を表2に示す。
上記、減磁率を測定した異方性ボンド磁石の残留磁束密度を、B-Hトレーサーにて測定した。その結果を表2に示す。
11 炉本体
12 処理容器
13 ヒータ
14 断熱材
15、16 温度計
17 温度測定器
21 ガス導入口
22 ガス排気口
23 炉床
S 分解生成物
24 主相粒子
25 粒界相
Claims (5)
- 合金組成がRxTyBz(xとyとzとは28.0≦x≦36.0、62.0≦y≦71.0、1.0≦z≦1.5の質量比を満たす)と、C、N、O、Al、Si、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Zr、Nb、Mo、In、Sn、Hf、Ta、Wおよびその他不可避元素の少なくとも一種類以上からなる原料合金を用いて得られる請求項1に記載のR-T-B系合金粉末。
- 請求項1または請求項2に記載のR-T-B系合金粉末と、樹脂と、を含む異方性ボンド磁石用コンパウンド。
- 請求項1または請求項2に記載のR-T-B系合金粉末を用いた異方性ボンド磁石。
- 請求項3の異方性ボンド磁石用コンパウンドを用いた異方性ボンド磁石。
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