Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
• • 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
  • H01F1/0577—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 sintered
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/11—Making amorphous alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C28/00—Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C45/00—Amorphous alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
  • H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/07—Metallic powder characterised by particles having a nanoscale microstructure
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C2202/00—Physical properties
  • C22C2202/02—Magnetic
• • 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

Definitions

• the invention relates to a method of manufacturing rare-earth magnets.
• Rare-earth magnets which use rare-earth elements such as lanthanoids are also called permanent magnets.
• Applications include motors in hard disk drives and magnetic resonance imaging (MRI) scanners, as well as drive motors in hybrid vehicles and electric cars.
• MRI magnetic resonance imaging
• Remanent magnetization (remanent magnetic flux density) and coercive force may be cited as indicators of the performance of these rare-earth magnets.
• the rise in heat generation associated with the miniaturization and trend toward higher current density in motors has prompted a greater desire for heat resistance also in the rare-earth magnets that are used. How to maintain the coercive strength of a magnet under high-temperature use is thus a major topic of research today in this technical field.
• Nd-Fe-B-based magnets which are one type of rare-earth magnet commonly used in drive motors for vehicles
• efforts are being made to increase their coercive force by, for example, reducing the size of the crystal grains, using alloys having a high neodymium content, and adding the heavy rare-earth elements like dysprosium and terbium, which have high coercive force performances.
• Rare-earth magnets include common sintered magnets in which the scale of the grains (main phase) making up the microstructure is about 3 ⁇ to 5 ⁇ , and nanocrystalline magnets in which the size of the crystal grains has been reduced to a nanoscale level of about 50 nm to 300 nm. Especially noteworthy among these at present are nanocrystalline magnets in which the amount of high-cost heavy rare-earth elements is reduced (or eliminated) while striving to decrease the size of the crystal grains.
• dysprosium which is used in large quantities, is discussed here. Because reserves of dysprosium occur predominantly in China and because China has placed restrictions on the production and export of dysprosium and other rare metals, the commodity price of dysprosium has been rising rapidly in fiscal 2011. Hence, one key challenge has been to develop low-dysprosium magnets which ensure coercive force performance while reducing the amount of dysprosium, and dysprosium-free magnets which ensure coercive force performance without the use of any dysprosium. This is one major factor that has increased the degree of attention being paid to nanocrystalline magnets.
• a method of manufacturing nanocrystalline magnets is summarized.
• a Nd-Fe-B-based metal melt for example, is rapidly solidified, and the resulting nanosize fine powder is pressure sintered, thereby producing a sintered body.
• Hot plastic working is carried out on the sintered body to impart magnetic anisotropy, producing a compact.
• Rare-earth magnets composed of a nanocrystalline magnet are produced by using various techniques to include in this compact a heavy rare-earth element having a high coercive force performance. Examples include the production methods disclosed in Japanese Patent Application Publication No. 2011-035001 (JP-2011-035001 A) and Japanese Patent Application Publication No. 2010-114200 (JP-2010- 114200 A).
• JP-2011-035001 A discloses a production process which vaporizes an evaporation material containing at least one of dysprosium and terbium onto a hot plastic-worked compact, thereby inducing grain boundary diffusion from the surface of the compact.
• An essential condition in this production process is high-temperature treatment at about 850°C to 1050°C in the evaporation material vaporization step. This temperature range was prescribed to enhance the remanent coercive force density and to suppress excessively rapid crystal grain growth.
• JP-2010-114200 A discloses a production process in which at least one element from among dysprosium (Dy), terbium (Tb) and holmium (Ho), or an alloy of at least one element from among copper (Cu), aluminum (Al), gallium (Ga), germanium (Ge), tin (Sn), indium (In), silicon (Si), phosphorus (P) and cobalt (Co), is brought into contact with the surface of a rare-earth magnet and heat-treated to effect grain boundary diffusion in such a way that the grain size does not exceed 1 ⁇ .
• Dy dysprosium
• Tb terbium
• Ho holmium
• Co cobalt
• JP-2010-114200 A it is mentioned here in JP-2010-114200 A that, when the temperature during heat treatment is in the range of 500°C to 800°C, an excellent balance is achieved between the diffusion effect by Dy, etc. to the crystal grain boundary phase and the crystal grain coarsening suppression effect by heat treatment, making it easier to obtain a rare-earth magnet having a high coercive force.
• the use of a Dy-Cu alloy and heat-treatment at 500°C to 900°C are mentioned.
• high-temperature treatment at about 1000°C or above is required in order to have this metal melt diffuse and infiltrate into a rare-earth magnet. As a result, it is impossible to suppress a coarsening of the crystal grains.
• the alloy in heat treatment within the range of 500°C to 800°C in JP-2010-114200 A is a solid phase and the Dy-Cu alloy or the like is diffused within the rare-earth magnet by solid phase diffusion, it can readily be appreciated that such diffusion takes time.
• This invention was conceived in light of the fact that coarsening of the crystal grains occurs in the high-temperature atmosphere when diffusing a modified alloy containing a high-melting heavy rare-earth element into the grain boundary phase and the fact that solid-phase diffusion of this modified alloy takes time.
• the invention provides a method of manufacture which, in contrast with conventional methods of manufacturing rare-earth magnets, is able to induce a modified alloy that increases the coercive force at low temperatures (particularly the coercive force in a high-temperature atmosphere) to infiltrate a rare-earth magnet compact, and can thereby produce rare-earth magnets having a high coercive force and also having a relatively high magnetization.
• the method of manufacturing rare-earth magnets includes: a first step of producing a compact by subjecting a sintered body, which is formed of a RE-Fe-B main phase having a nanocrystalline structure (where RE is at least one of neodymium and praseodymium) and a grain boundary phase of an RE-X alloy (where X is a metal element) located around the main phase, to hot plastic processing that imparts anisotropy; and a second step of producing a rare-earth magnet by melting a RE-Y-Z alloy which increases the coercive force of the compact (where Y is a transition metal element and Z is a heavy rare-earth element), together with the grain boundary phase, and liquid-phase infiltrating the RE-Y-Z alloy melt from a surface of the compact.
• a modified alloy having a melting point that is much lower than conventional modified alloys is used and the grain boundary phase and the modified alloy are melted together, thereby liquid-phase infiltrating a melt of the modified alloy into the grain boundary phase while the latter is in a molten state.
• this is a method for manufacturing nanocrystalline magnets having, in particular, a high coercive force in a high-temperature atmosphere (e.g., 150°C to 200°C), and also having a relatively high magnetization.
• a melt of the composition making up the rare-earth magnet is liquid quenched, producing a rapidly cooled ribbon composed of fine crystal grains. This is then loaded into a die and sintered under the application of pressure with a punch and thereby consolidated, giving an isotropic sintered body composed of an RE-Fe-B main phase (wherein RE is at least one of neodymium (Nd) and praseodymium (Pr), and is more specifically one, two or more from among Nd, Pr and Nd-Pr) having a nanocrystalline structure and a grain boundary phase composed of an RE-X alloy (wherein X is a metal element) around the main phase.
• RE is at least one of neodymium (Nd) and praseodymium (Pr), and is more specifically one, two or more from among Nd, Pr and Nd-Pr
• RE-X alloy wherein X is a metal element
• the sintered body is subjected to hot plastic working so as to impart anisotropy, thereby giving a compact.
• hot plastic working in addition to the working temperature and the working time, adjustment of the plastic strain rate is also an important parameter.
• the RE-X alloy making up the grain boundary phase of this compact differs also according to the ingredients of the main phase.
• the RE-X alloy may be an alloy of Nd with at least one from among cobalt (Co), iron (Fe) and gallium (Ga), such as any one of Nd-Co, Nd-Fe, Nd-Ga, Nd-Co-Fe and Nd-Co-Fe-Ga, or a mixture of two or more thereof, and is in an Nd-rich state.
• the RE-X alloy may be in a Pr-rich state similarly to the cases where RE is Nd.
• the inventors have identified the melting points of Nd-Co, Nd-Fe, Nd-Ga, Nd-Co-Fe and Nd-Co-Fe-Ga, and of grain boundary phases where these are present in admixture as being in the vicinity of about 600°C (because there is some variability due to the ingredients and the ratios thereof, in the range of about 550°C to about 650°C).
• the grain size of the main phase it is preferable for the grain size of the main phase to be in the range of 50 nm to 300 nm. More preferably, the average grain size of the main phase is about 200nm. This is based on the finding by the inventors that, in cases where a main phase having such a grain size range is employed in nanocrystalline magnets, the grain size does not increase.
• the grain boundary phase making up this compact is melted, thus causing a RE-Y-Z alloy (wherein Y is a transition metal element, and Z is a heavy rare-earth element), which is a modified alloy, to liquid-phase infiltrate the compact from the surface thereof.
• the RE-Y-Z alloy melt thereby infiltrates into the molten-state grain boundary phase of the compact and, while giving rise to structural changes at the interior of the compact, produces a rare-earth magnet having an increased coercive force.
• a melt of the Nd alloy in the range of about 600°C to about 650°C infiltrates into the molten-state grain boundary phase.
• Transition metal elements that may be employed include any one from among, for example, Cu, Fe, Mn, Co, Ni, Zn and Ti.
• "Heavy rare-earth elements” that may be employed include any one from among, for example, Dy, Tb and Ho.
• infiltration of a modified alloy under temperature conditions of about 600°C may also be regarded as desirable because nanocrystalline magnets, unlike sintered magnets, undergo pronounced coarsening of the crystal grains when placed for about 10 minutes in a high-temperature atmosphere of about 800°C. Even in cases where a 70Dy-30Cu alloy is used, because this has a melting point of 790°C, high-temperature treatment of about 800°C is required, making it impossible to suppress coarsening of the crystal grains.
• the melting point of the alloy differs with the ingredient ratio therein (e.g., the melting point of the alloy 60Nd-30Cu-10Dy is 533°C, and the melting point of the alloy
• such modified alloys have melting points which are generally less than 600°C; hence, the alloy has a low melting point which is similar to that of the grain boundary phase.
• the crystal grains have a flattened shape which is perpendicular to the direction of orientation, and the grain boundaries substantially parallel to the axis of anisotropy are curved or bent and tend not to be composed of specific planes.
• the interfaces of the crystal grains become distinct, i magnetic decoupling between the crystal grains proceeds, and the coercive force increases.
• the sides of the crystal grains parallel to the axis of anisotropy are not yet specific planes.
• the crystal grains have a shape such that the planar shape as seen from a
• direction perpendicular to the axis of anisotropy becomes rectangular or a shape that is approximately rectangular, and the surfaces of the crystal grain become a polyhedron (a hexahedron (rectangular prism), an octahedron, or a solid similar thereto) surrounded by low-index (Miller index) planes.
• a hexahedron the inventors have determined that the axis of orientation is formed in the (001) plane (the direction of easy magnetization (c axis) being the top and bottom sides of the hexahedron), and the lateral sides are formed of (110), (100) or plane indices similar thereto.
• the inventive method of manufacturing rare-earth magnets uses a RE-Y-Z alloy (wherein Y is a transition metal element, and Z is a heavy rare-earth element), which is a low-melting modified alloy, to liquid-phase infiltrate a modified alloy melt into the molten-state grain boundary phase of a compact obtained by subjecting a sintered body composed of a RE-Fe-B main phase (wherein RE is at least one of Nd and Pr) having a nanocrystalline structure and a grain boundary phase of RE-X alloy located around the main phase to hot plastic working.
• RE-Y-Z alloy wherein Y is a transition metal element, and Z is a heavy rare-earth element
• FIGS. 1A, B and C are schematic diagrams illustrating, in the order FIG.1A, IB and
• FIG. 2 A is a diagram depicting the microstructure of a sintered body obtained via the step shown in FIG. IB, and FIG. 2B is a diagram depicting the microstructure of a compact in FIG. 1C;
• FIG. 3A is a diagram illustrating the second step in an embodiment of the inventive method of manufacturing rare-earth magnets
• FIG. 3B is a diagram depicting the microstructure of a rare-earth magnet during modification of the structure with a modified alloy
• FIG. 3C is a diagram depicting the microstructure of a rare-earth magnet in which modification of the structure with a modified alloy is complete
• FIG. 4 is a graph showing the experimental results relating to magnetization and coercive force before and after the diffusion of a modified alloy.
• FIGS. 1A, IB and 1C are schematic diagrams illustrating the first step in an embodiment of the inventive method of manufacturing a rare-earth magnet
• FIG. 3A is a diagram illustrating the second step in the inventive method of manufacturing rare-earth magnets
• FIG. 2A is a diagram depicting the microstructure of the sintered body shown in FIG. IB
• FIG. 2B is a diagram depicting the microstructure of the compact in FIG. 1C
• FIG. 3B is a diagram depicting the microstructure of a rare-earth magnet during modification of the structure with a modified alloy
• FIG. 3C is a diagram depicting the microstructure of a rare-earth magnet in which modification of the structure with a modified alloy is complete.
• an alloy ingot is high-frequency induction melted by a single-roll melt spinning process in a furnace (not shown) under a reduced-pressure (50 kPa or below) argon gas atmosphere.
• a rapidly cooled ribbon B is produced by spraying a melt having a structure that imparts this rare-earth magnet onto a copper roll R, and the ribbon B is coarsely ground.
• the coarsely ground rapidly cooled ribbon B is loaded into a cavity defined by a carbide die D and a carbide punch P which slides through a hollow interior of the die D, then is heated, while applying pressure thereto with the carbide punch P, by passing an electrical current therethrough in the direction of pressure application (X direction).
• X direction the direction of pressure application
• the Nd-X alloy making up the grain boundary phase is in a Nd-rich state and is composed of an alloy of at least one from among Co, Fe and Ga, such as any one of Nd-Co, Nd-Fe, Nd-Ga, Nd-Co-Fe and Nd-Co-Fe-Ga, or is a mixture of two or more thereof.
• the sintered body S exhibits an isotropic crystal structure in which the grain boundary phase BP fills the gaps between the nanocrystalline grains MP (main phase).
• a carbide punch P is brought into direct contact with the endfaces in the longitudinal direction (in FIG.
• the horizontal direction serves as the lengthwise direction) of the sintered body S, and hot plastic working is carried out while pressing (in the X direction) with the carbide punch P.
• a compact C with a crystal structure having anisotropic nanocrystalline grains MP is thereby produced (the above operation serves as the first step).
• the nanocrystalline grains MP have a flattened shape, with the interfaces that are substantially parallel with the axis of anisotropy being curved or bent and not composed of specific planes.
• the compact C that has been produced is placed inside a high-temperature furnace H equipped with an internal heater, a modified alloy M composed of Nd-Y-Z alloy (wherein Y is a transition metal element, and Z is a heavy rare-earth element) is brought into contact with the compact C, and the furnace interior is placed under a high-temperature atmosphere.
• a modified alloy M composed of Nd-Y-Z alloy (wherein Y is a transition metal element, and Z is a heavy rare-earth element) is brought into contact with the compact C, and the furnace interior is placed under a high-temperature atmosphere.
• any one from among Cu, Fe, Mn, Co, Ni, Zn and Ti may be employed as the transition metal element Y, and any one from among Dy, Tb and Ho may be employed as the heavy rare-earth metal element Z.
• Illustrative examples include Nd-Cu-Dy alloys and Nd-Cu-Tb alloys.
• the melting point of the grain boundary phase composed of Nd-Co, Nd-Fe, Nd-Ga, Nd-Co-Fe, Nd-Co-Fe-Ga or a mixture thereof varies somewhat with the ingredients and the proportions thereof, but is generally in the vicinity of 600°C (taking this variability into account, the range is from about 550°C to about 650°C).
• the melting points are about the same as or lower than the melting point of the grain boundary phase BP.
• the grain boundary phase BP melts, and the Nd-Cu-Dy alloy or Nd-Cu-Tb alloy serving as the modified alloy also melts.
• the modified alloy melt liquid-phase infiltrates in this manner into the molten-state grain boundary phase BP, the diffusion efficiency and diffusion rate are far better than in cases where a Dy-Cu alloy or the like is solid-phase diffused into the grain boundary phase as in conventional manufacturing methods, enabling diffusion of the modified alloy to be achieved in a short time.
• rare-earth magnets thus obtained by a manufacturing method according to the embodiments of the invention, owing to the use of a compact obtained by carrying out hot plastic working so as to impart anisotropicity to the sintered body and owing also to the liquid-phase infiltration of a modified alloy melt composed of a Nd- Y-Z alloy (wherein Y is a transition metal element, and Z is a heavy rare-earth element) into a molten-state grain boundary phase, it appears that residual strain which arises due to hot plastic working is eliminated by contact with the modified alloy melt, and also that the coercive force is improved by the reduction in size of the crystal grains and the promotion of magnetic decoupling between the crystal grains.
• a modified alloy melt composed of a Nd- Y-Z alloy (wherein Y is a transition metal element, and Z is a heavy rare-earth element) into a molten-state grain boundary phase
• the inventors conducted an experiment in which they produced rare-earth magnets that are nanocrystalline magnets by employing the above-described manufacturing method of the invention and they similarly produced rare-earth magnets using conventional modified alloys as the modified alloy that is infiltrated into the grain boundary phase. They then measured the magnetization and coercive force of each of the specimens, both before and after diffusion of the modified alloy, and compared the results.
• the sintered body thus formed was plastic worked at a working temperature of 750°C, a working ratio of 70% and a strain rate of 1/s, thereby producing a compact prior to diffusion of the modified alloy.
• top and bottom sides of the compact were coated with a modified alloy, and the coated compact was placed in a titanium vessel.
• the interior of the vessel was evacuated or placed under an argon atmosphere, and diffusion/infiltration of the modified alloy was carried out for 2 hours under the conditions in Table 1 below, thereby producing rare-earth magnets.
• the specimens thus produced were each magnetically measured using a pulsed excitation-type magnetic property measurement system, and the magnetization ratio before and after diffusion and the amount of increase in coercive force before and after diffusion were measured. Those results are shown in Table 2 below and in FIG. 4.
• Comparative Examples 1 and 2 it was possible to increase the coercive force by the diffusion of a Nd-Cu alloy (the coercive force in Comparative Example 2 was about the same as that in Example 1). In Comparative Example 2 in particular, the decrease in magnetization was pronounced.
• Comparative Examples 3 and 4 in the case of Comparative Example 3, wherein the working temperature during diffusion of the Dy-Cu alloy was low, it was found that the modified alloy did not melt, modified alloy did not sufficiently diffuse into the grain boundary phase, and there was substantially no rise ' in the coercive force. In the case of Comparative Example 4, wherein high-temperature working was carried out, it was found that the crystal grains ended up coarsening to a size of 1 ⁇ or more, the structure broke down, and the rise in coercive force was small.

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