EP0532701A1 - Matieres magnetiques ameliorees et leur procede de production - Google Patents

Matieres magnetiques ameliorees et leur procede de production

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Publication number
EP0532701A1
EP0532701A1 EP91914184A EP91914184A EP0532701A1 EP 0532701 A1 EP0532701 A1 EP 0532701A1 EP 91914184 A EP91914184 A EP 91914184A EP 91914184 A EP91914184 A EP 91914184A EP 0532701 A1 EP0532701 A1 EP 0532701A1
Authority
EP
European Patent Office
Prior art keywords
permanent magnet
temperature
nitrogen
rare earth
alloy
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91914184A
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German (de)
English (en)
Other versions
EP0532701A4 (en
Inventor
Yakov Bogatin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
SPS Technologies LLC
Original Assignee
SPS Technologies LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/535,460 external-priority patent/US5122203A/en
Application filed by SPS Technologies LLC filed Critical SPS Technologies LLC
Publication of EP0532701A1 publication Critical patent/EP0532701A1/fr
Publication of EP0532701A4 publication Critical patent/EP0532701A4/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • 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%
    • 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
    • B22F1/14—Treatment of metallic powder
    • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
    • 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
    • H01F1/0551—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0552—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 in the form of particles, e.g. rapid quenched powders or ribbon flakes with a protective layer
    • 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
    • H01F1/0555—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together
    • H01F1/0557—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together sintered
    • 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
    • H01F1/0572—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 with a protective layer
    • 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
    • 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
    • H01F41/026—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 protecting methods against environmental influences, e.g. oxygen, by surface treatment
    • 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
    • B22F3/24—After-treatment of workpieces or articles
    • B22F2003/248—Thermal after-treatment
    • 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
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps
    • 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
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
    • 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

Definitions

  • This invention generally relates to magnetic materials and, more particularly, to rare earth- containing powders, compacts and permanent magnets having an increased Curie temperature, and a process for producing the same.
  • Permanent magnet materials currently in use include alnico, hard ferrite and rare earth/cobalt magnets. Recently, new magnetic materials have been introduced containing iron, various rare earth elements and boron. Such magnets have been prepared from melt quenched ribbons and also by the powder metallurgy technique of compacting and sintering, which was previously employed to produce samarium cobalt magnets. Suggestions of the prior art for rare earth permanent magnets and processes for producing the same include: U.S. Patent No. 4,597,938, Matsuura et al.
  • U.S. Patent No. 4,601,875, Yamamoto et al. teaches permanent magnet materials of the Fe-B-R type produced by: preparing a metallic powder having a mean particle size of 0.3-80 microns and a composition of, in atomic percent, 8-30% R representing at least one of the rare earth elements inclusive of Y, 2-28% B and the balance Fe; compacting; sintering at a temperature of 900-1200°C; and, thereafter, subjecting the sintered bodies to heat treatment at a temperature lying between the sintering temperature and 350°C.
  • Co and additional elements M may be present.
  • U.S. Patent No. 4,802,931, Croat discloses an alloy with hard magnetic properties having the basic formula RE 1 _ ⁇ (TM 1 B y ) x -
  • RE represents one or more rare earth elements including scandium and yttrium in Group IIIA of the periodic table and the elements from atomic number 57 (lanthanum) through 71 (lutetium) .
  • TM in this formula represents a transition metal taken from the group consisting of iron or iron mixed with cobalt, or iron and small amounts of other metals such as nickel, chromium or manganese.
  • crushing an alloy mass to make suitable powder in the aforementioned environment is also disadvantageous since the powder produced has a high density of certain defects in the crystal structure which adversely affect the magnetic properties. Additionally, crushing in the organic liquid environment unduly complicates the attainment of the desired shape, size, structure, magnetic field orientation and magnetic properties of the powders and resultant magnets since the organic liquid environments have a relatively high viscosity which interferes with achieving the desired results. Moreover, attempts to passivate the surfaces of the powder particles by coating them with a protective substance, such as a resin, nickel or the like, during and after crushing is a generally ineffective and complicated process which increases the cost of manufacturing.
  • a protective substance such as a resin, nickel or the like
  • This invention relates to a process for producing a rare earth-containing material capable of being formed into a permanent magnet comprising crushing a rare earth-containing alloy and treating the alloy with a passivating gas at a temperature below the phase transformation temperature of the alloy.
  • This invention further relates to a process for producing a rare earth-containing powder comprising crushing a. rare earth-containing alloy in a passivating gas at a temperature from ambient temperature to a temperature below the phase transformation temperature of the material.
  • This invention also relates to a process for producing a rare earth-containing powder comprising crushing an alloy in water, drying the crushed alloy material at a temperature below the phase transformation temperature of the material, and treating the crushed alloy material with a passivating gas at a temperature from the ambient temperature to a temperature below the phase transformation temperature of the material. Additionally, this invention relates to a process for producing a rare earth-containing powder compact comprising crushing a rare earth- containing alloy in water, compacting the crushed alloy material, drying the compacted alloy material at a temperature below the phase transformation temperature of the material, and treating the compacted alloy material with a passivating gas at a temperature from ambient temperature to a temperature below the phase transformation temperature of the material.
  • the alloy can comprise, in atomic percent of the overall composition, from about 12% to about 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and the balance iron.
  • Other rare earth- containing alloys suitable for use in producing permanent magnets utilizing the powder metallurgy technique such as samarium cobalt alloy, can also be used.
  • the alloys are crushed to a particle size of from about 0.05 microns to about 100 microns and, preferably, to a particle size of from l micron to 40 microns. If the alloys are crushed in water, the crushed or compacted alloy material can be vacuum dried or dried with an inert gas, such as argon or helium.
  • the passivating gas can be nitrogen, carbon dioxide or a combination of nitrogen and carbon dioxide. If nitrogen is used as the passivating gas, the resultant powder or compact has a nitrogen surface concentration of from about 0.4 to about 26.8 atomic percent. Moreover, if carbon dioxide is used as the passivating gas, the resultant powder or compact has a carbon surface concentration of from about 0.02 to about 15 atomic percent.
  • the rare earth-containing powder and powder compact produced in accordance with the present invention are non-pyrophoric and resistant to oxidation. Furthermore, the excellent properties displayed by the powders of this invention make them suitable for use in producing magnets, such as bonded or pressed magnets.
  • the present invention further relates to the production of an improved permanent magnet comprising the steps for producing the rare earth-containing powder set forth above and then compacting the crushed alloy material, sintering the compacted alloy material at a temperature of from about 900°C to about 1200°C, and heat treating the sintered material at a temperature of from about 200°C to about 1050°C.
  • the present invention also relates to the production of an improved permanent magnet comprising the steps for producing the rare earth-containing powder compact set forth above and then sintering the compacted alloy material at a temperature of from about 900°C to about 1200°C, and heat treating the sintered material at a temperature of from about 200°C to about 1050°C. Additionally, according to the present invention, it is possible to increase the Curie temperature of the aforesaid rare earth-containing material by following the above-mentioned processing steps for the various embodiments of this invention.
  • the present invention relates to a process for producing a rare earth-containing material capable of being formed into a permanent magnet having an increased Curie temperature comprising crushing a rare earth-containing alloy and treating the alloy with an amount of a passivating gas at a temperature below the phase transformation temperature of the alloy, such that the Curie temperature of the material is increased when the material is formed into a permanent magnet.
  • the Curie temperature can be increased at least about 100°C.
  • the improved permanent magnet in accordance with the present invention includes the type of magnet comprised of, in atomic percent of the overall composition, from 12% to 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and at least 52% iron, wherein the improvement comprises a nitrogen surface concentration of from about 0.4 to about 26.8 atomic percent.
  • the improved permanent magnet can also have a carbon surface concentration of from about 0.02 to about 15 atomic percent if carbon dioxide is used as a passivating gas. These improved permanent magnets have a high resistance to corrosion and superior magnetic properties. Furthermore, these improved permanent magnets have a higher Curie temperature than a corresponding magnet having said overall composition with no surface concentration of nitrogen or carbon.
  • FIG. 1 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /Pb of 1:16 and grinding time of 30 minutes.
  • FIG. 2 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P of 1:16 and grinding time of 60 minutes.
  • FIG. 3 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P b of 1:16 and grinding time of 90 minutes.
  • FIG. 4 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P b ° f 1:16 and grinding time of 120 minutes.
  • FIG. 5 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P b of 1:24 and grinding time of 15 minutes.
  • FIG. 6 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P b of 1:24 and grinding time of 30 minutes.
  • FIG. 7 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P of 1:24 and grinding time of 60 minutes.
  • FIG. 8 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P b °f 1:24 and grinding time of 90 minutes.
  • FIG. 9 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P of 1:32 and grinding time of 15 minutes.
  • FIG. 10 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with P a /P b of 1:32 and grinding time of 30 minutes.
  • FIG. 11 is a graph showing the particle size and shape distribution for Nd-Fe-B powder produced in accordance with the present invention with ⁇ > a /P- b of 1:32 and grinding time of 60 minutes.
  • FIG. 12 is a photomicrograph at 650X magnification of Nd-Fe-B powder produced in accordance with the present invention and oriented in a magnetic field.
  • FIG. 13 is a photomicrograph at 1600X magnification of Nd-Fe-B powder produced in accordance with the present invention.
  • FIG. 14 is a photomicrograph at 1100X magnification of Nd-Fe-B powder produced by conventional powder metallurgy technique and oriented in a magnetic field.
  • FIG. 15 is an X-ray diffraction pattern of Nd-Fe-B powder produced in accordance with the present invention.
  • FIG. 16 is an X-ray diffraction pattern of Nd-Fe-B powder produced by conventional powder metallurgy technique.
  • FIG. 17 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) ma ⁇ (MGOe) on the horizontal axis and comparing a conventional Nd-Fe-B magnet with examples having nitrogen surface concentrations in accordance with the present invention.
  • FIG. 18 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis and comparing a conventional Nd-Fe-B magnet with examples having carbon surface concentrations in accordance with the present invention.
  • FIG. 19 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis and comparing a conventional Nd-Fe-B magnet with examples having nitrogen and carbon surface concentrations in accordance with the present invention.
  • FIG. 20 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for an example having nitrogen surface concentration in accordance with the present invention.
  • FIG. 21- is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) ma ⁇ (MGOe) on the horizontal axis for an example having nitrogen surface concentration in accordance with the present invention.
  • FIG. 22 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for an example having nitrogen surface concentration in accordance with the present invention.
  • FIG. 21- is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) ma ⁇ (MGOe) on the horizontal axis for an example having nitrogen surface concentration in accordance with the present invention.
  • FIG. 22 is a graph showing the relationship between residual in
  • FIG. 23 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a conventional Nd-Fe-B magnet example.
  • FIG. 24 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a sintered magnet example having carbon surface concentration in accordance with the present invention.
  • FIG. 25 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a sintered magnet example having carbon surface concentration in accordance with the present invention.
  • FIG. 26 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a sintered magnet example having carbon surface concentration in accordance with the present invention.
  • FIG. 27 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) ma ⁇ (MGOe) on the horizontal axis for a sintered magnet example having nitrogen surface concentration in accordance with the present invention.
  • FIG. 26 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) ma ⁇ (MGOe) on the horizontal axis for a sintered magnet example having nitrogen surface concentration in accordance with the present invention.
  • FIG. 28 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a sintered compact example having carbon surface concentration in accordance with the present invention.
  • FIG. 29 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a sintered compact example having carbon and nitrogen surface concentration in accordance with the present invention.
  • FIG. 30 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a sintered compact example having carbon surface concentration in accordance with the present invention.
  • FIG. 31 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for a sintered compact example having nitrogen surface concentration in accordance with the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • the present invention relates to a process for producing a rare earth-containing material capable of being formed into a permanent magnet comprising crushing a rare earth-containing alloy and treating the alloy with a passivating gas at a temperature below the phase transformation temperature of the material. More particularly, the present invention relates to a process for producing a rare earth-containing material capable of being formed into a permanent magnet having an increased Curie temperature comprising crushing a rare earth-containing alloy and treating the alloy with a sufficient amount of a passivating gas at a temperature below the phase transformation temperature of the alloy so ' that the Curie temperature of the material is increased when the material is formed into a permanent magnet.
  • the present invention relates to a process for producing a rare earth- containing powder comprising crushing a rare earth- containing alloy in a passivating gas at a temperature from ambient temperature to a temperature below the phase transformation temperature of the material.
  • the powder can be formed into a permanent magnet having an increased Curie temperature.
  • the present invention relates to a process for producing a rare earth- containing powder comprising: crushing a rare earth- containing alloy in water; drying the crushed alloy material at a temperature below the phase transformation temperature of the material; and treating the crushed alloy material with a passivating gas at a temperature from ambient temperature to a temperature below the phase transformation temperature of the material.
  • the present invention further relates to a process for producing a permanent magnet comprising the above-mentioned processing steps to produce a powder and then performing the additional steps of compacting the crushed alloy material, sintering the compacted alloy material at a temperature of from about 900°C to about 1200°C, and heat treating the sintered material at a temperature of from about 200°C to about 1050°C. More particularly, the present invention relates to a process for increasing the Curie temperature of a permanent magnet comprising the above steps.
  • the present invention relates to a process for producing a rare earth-containing powder compact comprising: crushing a rare earth-containing alloy in water; compacting the crushed alloy material; drying the compacted alloy material at a temperature below the phase transformation temperature of the material; and treating the compacted alloy material with a passivating gas at a temperature from ambient temperature to a temperature below the phase transformation temperature of the material.
  • this invention relates to a process for producing a permanent magnet comprising the above- mentioned processing steps to produce a powder compact and then performing the additional steps of sintering the compacted alloy material at a temperature of from about 900°C to about 1200°C, and heat treating the sintered material at a temperature of from about 200°C to about 1050°C. More particularly, this invention also relates to a process for increasing the Curie temperature of a permanent magnet comprising the above steps.
  • the first processing step of the instant invention involves placing an ingot or piece of a rare earth-containing alloy in a crushing apparatus and crushing the alloy.
  • the crushing can occur in either water or a passivating gas. It is believed that any rare earth-containing alloy suitable for producing powders, compacts and permanent magnets by the conventional powder metallurgy method can be utilized.
  • the alloy can have a base composition of: R-Fe-B, R-Co-B, and R-(Co,Fe)-B wherein R is at least one of the rare earth metals, such as Nd-Fe-B; RCo 5 , R(Fe,Co) 5 , and RFe 5 , such as SmCo 5 ; R 2 Co 17 , R 2 (Fe,Co) 17 , and R 2 Fe 17 , such as Sm 2 Co 17 and Sm 2 Fe 17 ; mischmetal-Co, mischmetal-Fe and mischmetal-(Co,Fe) ; Y-Co, Y-Fe and Y- (Co,Fe) ; or other similar alloys known in the art.
  • the R-Fe-B alloy compositions disclosed in U.S. Patent Nos. 4,597,938 and 4,802,931, the texts of which are incorporated by reference herein, are particularly suitable for use in accordance with the present invention.
  • the rare earth- containing alloy comprises, in atomic percent of the overall composition, from about 12% to about 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and the balance iron.
  • the rare earth element is neodymium and/or praseodymium.
  • RM 5 and 2 M 17 type rare earth alloys wherein R is at least one rare earth element selected from the group defined above and M is at least one metal selected from the group consisting of Co, Fe, Ni, and Mn may be utilized. Additional elements Cu, Ti, Bi, V, Nb, Ta, Cr, Mo, W, Mn, Al, Sb, Ge, Sn, Zr and Hf, may also be utilized. RCo 5 and R 2 Co 17 are preferred for this type.
  • the alloys, as well as the powders, compacts and magnets produced therefrom in accordance with the present invention may contain, in addition to the above-mentioned base compositions, impurities which are entrained from the industrial process of production.
  • the alloys are crushed in water to produce particles having a particle size of from about 0.05 microns to about 100 microns and, preferably, from 1 micron to 40 microns, although larger size particles, such as up to about 300 microns, can also be utilized.
  • the particle size is from 2 to 20 microns.
  • the time required for crushing is not critical and will, of course, depend upon the efficiency of the crushing apparatus.
  • the crushing is performed in water to prevent oxidation of the crushed alloy material.
  • water has a low coefficient of viscosity and, therefore, crushing in water is more effective and faster than crushing in organic liquids presently utilized in the art.
  • crushing in water provides a higher defect density of domain wall pinning sites in the individual alloy particles, thereby providing better magnetic properties for the magnets produced from the powder or powder compact.
  • the size and shape of the individual alloy particles is optimized for compacting of the powder in a magnetic field to produce magnets.
  • the type of water utilized is not critical. For example, distilled, deionized or non-distilled water may be utilized, but distilled is preferred.
  • the crushed alloy material is then dried at a temperature below the phase transformation temperature of the material. More particularly, the crushed alloy material is dried thoroughly at a temperature which is sufficiently low so that phase transformation of the alloy material is not induced.
  • phase transformation temperature means the temperature at which the stoichiometry and crystal structure of the base rare earth-containing alloy changes to a different stoichiometry and crystal structure.
  • crushed alloy material having a base composition of Nd-Fe-B will undergo phase transformation at a temperature of approximately 580°C. Accordingly, the Nd-Fe-B crushed alloy material should be dried at a temperature below about 580°C.
  • phase transformation temperature necessary for the alloy material utilized will vary depending on the exact composition of the material and this temperature can be determined experimentally for each such composition.
  • the wet crushed alloy material is first put in a centrifuge or other appropriate equipment for quickly removing most of the water from the material.
  • the material can then be vacuum dried or dried with an inert gas, such as argon or helium.
  • the crushed alloy material can be effectively dried by the flow or injection of the inert gas at a pressure below 760 torr. Nevertheless, regardless of the drying technique, the drying must be performed at a temperature below the aforementioned phase transformation temperature of the material.
  • the crushed alloy material is first compacted before drying to form wet compacted material.
  • the material is compacted at a pressure of 0.5 to 12 T/cm 2 .
  • the pressure for compaction is not critical.
  • the resultant compact should have interconnected porosity and sufficient green strength to enable the compact to be handled.
  • the interconnected porosity can be obtained during drying of the compact.
  • the term "interconnected porosity" as used herein means a network of connecting pores is present in the compact in order to permit a fluid or gas to pass through the compact.
  • the compaction is performed in a magnetic field to produce anisotropic permanent magnets.
  • a magnetic field of about 7 to 15 kOe is applied in order to align the particles.
  • a magnetic field is not applied during compaction when producing isotropic permanent magnets.
  • the compacted alloy material can be thereafter dried at a temperature below the phase transformation temperature of the material as described above.
  • the compaction and drying steps can be combined if desired so that the compaction and drying occur simultaneously.
  • the compaction and drying steps can even be reversed (i.e. dry the crushed alloy material first and then compact the material) if a protective atmosphere is provided until the compact is treated with a passivating gas.
  • the crushed or compacted alloy material is treated with a passivating gas at a temperature from ambient temperature to a temperature below the phase transformation temperature of the material. If the wet crushed or compacted material was dried in a vacuum box, then the material can be treated with the passivating gas by injecting the gas into the box.
  • passivating gas as used herein means a gas suitable for passivation of the surface of the crushed material, powder or compacted powder particles so as to produce a thin layer on the surface of the particles in order to protect it from corrosion and/or oxidation.
  • the passivating gas can be nitrogen, carbon dioxide or a combination of nitrogen and carbon dioxide.
  • the temperature at which the powder or compacted powder particles is treated is critical and must be below the phase transformation temperature of the material.
  • the maximum temperature for treatment must be below about 580°C when a Nd-Fe-B composition is used for the material.
  • crushed or compacted alloy material of the Nd-Fe-B type is treated with the passivating gas from about one minute to about 60 minutes at a temperature from about 20°C to about 580°C and, advantageously, at a temperature of about 175°C to 225°C.
  • the powder is produced by placing an ingot or piece of the rare earth-containing alloy in a crushing apparatus, such as an attritor or ball mill, and then purging the apparatus with a passivating gas to displace the air in the apparatus.
  • the alloy is crushed in the passivating gas to a particle size of from about 0.05 microns to about 100 microns and, preferably, from 1 micron to 40 microns, although larger size particles, such as up to about 300 microns, can also be utilized.
  • the time required for crushing is not critical and will, of course, depend upon the efficiency of the crushing apparatus.
  • the crushing apparatus may be set-up to provide a continuous operation for crushing the alloy in a passivating gas.
  • the temperature at which the alloy material is crushed in passivating gas is critical and must be below the phase transformation temperature of the material as defined above.
  • the passivating gas pressure and the amount of time the alloy material is crushed in the passivating gas must be sufficient to obtain the nitrogen or carbon surface concentration in the resultant powder and magnet as noted below.
  • the resultant powder or powder compact When nitrogen is used as the passivating gas in accordance with the present invention, the resultant powder or powder compact has a nitrogen surface concentration of from about 0.4 to about 26.8 atomic percent and, preferably, 0.4 to 10.8 atomic percent. Furthermore, when carbon dioxide is used as the passivating gas, the resultant powder or powder compact has a carbon surface concentration of from about 0.02 to about 15 atomic percent and, preferably, 0.5 to 6.5 atomic percent. When a combination of nitrogen and carbon dioxide is utilized, the resultant powder or powder compact can have a nitrogen surface concentration and carbon surface concentration within the above-stated ranges.
  • the powder or powder compact having the nitrogen or carbon surface concentration defined herein is capable of being formed into a permanent magnet having an increased Curie temperature as compared to a corresponding permanent magnet formed from powder or powder compact having the same overall composition only with no such nitrogen or carbon surface concentration.
  • the usual method of determining Curie temperatures involves measurement of magnetization in a direction that is parallel to the direction of easy magnetization of the sample and that is the method that has been adopted for the purpose of this application as a basis for expressing Curie temperatures.
  • surface concentration means the concentration of a particular element in the region extending from the surface to a depth of 25% of the distance between the center of the particle and surface.
  • the surface concentration for a particle having a size of 5 microns will be the region extending from the surface to a depth of 0.625 microns.
  • the region extends from the surface to a depth of 10% of the distance between the center of the particle and surface.
  • This surface concentration can be measured by Auger electron spectroscopy (AES) , as can be appreciated by those skilled in the art.
  • AES Auger electron spectroscopy
  • the present invention further provides for an unique non-pyrophoric rare earth-containing powder and powder compact comprising, in atomic percent of the overall composition, from about 12% to about 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and at least 52% iron, and further having a nitrogen surface concentration of from about 0.4 to about 26.8 atomic percent.
  • rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium,
  • the rare earth element of the alloy powder or powder compact is neodymium and/or praseodymium and the nitrogen surface concentration is from 0.4 to 10.8 atomic percent.
  • the present invention provides for an unique non-pyrophoric rare earth- containing powder and powder compact comprising, in atomic percent of the overall composition, from 12% to 24% of at least one rare earth element, selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and at least 52% iron, and further having a carbon surface concentration of from about 0.02 to about 15 atomic percent.
  • the rare earth element is neodymium and/or praseodymium and the carbon surface concentration is from 0.5 to 6.5 atomic percent.
  • the above-mentioned rare earth-containing powders and powder compacts are not only non-pyrophoric, but also resistant to oxidation and can be used to produce permanent magnets having superior magnetic properties and increased Curie temperatures.
  • the present invention further encompasses a process for producing a permanent magnet, which was discovered to have an unexpectedly increased Curie temperature. Therefore, the present invention also encompasses a process for increasing the Curie temperature of a permanent magnet.
  • this process comprises: a) crushing a rare earth-containing • alloy in a passivating gas for about 1 minute to about 60 minutes at a temperature from about 20°C to about 580°C to a particle size of from about 0.05 microns to about 100 microns, said alloy comprising, in atomic percent of the overall composition, of from about 12% to about 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and the balance iron; b) compacting the crushed alloy material; c) sintering the compacted alloy material at a temperature of from about 900°C to about 1200°C; and
  • the crushing step (step a) is the same as disclosed above for producing powder when the alloy is crushed in a passivating gas.
  • This process provides a permanent magnet having an increased Curie temperature as compared to a corresponding permanent magnet produced from a rare earth-containing alloy having the same overall composition only not treated with a passivating gas.
  • the process for producing a permanent magnet and for increasing the Curie temperature of a permanent magnet in accordance with the present invention comprises: a) Crushing a rare earth-containing alloy in water to a particle size of from about 0.05 microns to about 100 microns, the rare earth-containing alloy comprising, in atomic percent of the overall composition, of from about 12% to about 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and the balance iron; b) Drying the crushed alloy material at a temperature below the phase transformation temperature of the material; c) Treating the crushed alloy material with a passivating gas from about
  • the powders are subsequently compacted, preferably at a pressure of 0.5 to 12 T/cm 2 .
  • the pressure for compaction is not critical.
  • the compaction is performed in a magnetic field to produce anisotropic permanent magnets.
  • a magnetic field of about 7 to 15 kOe is applied in order to align the particles.
  • a magnetic field is not applied during compaction when producing isotropic permanent magnets.
  • the compacted alloy material is sintered at a temperature of from about 900°C to about 1200°C and, preferably, 1000°C to 1180°C.
  • the sintered material is then heat treated at a temperature of from about 200°C to about 1050°C.
  • This process also provides a permanent magnet having an increased Curie temperature as compared to a corresponding permanent magnet produced from a rare earth-containing alloy having the same overall composition only not treated with a passivating gas.
  • the process for producing a permanent magnet and for increasing the Curie temperature of a permanent magnet in accordance with the present invention comprises: a) crushing a rare earth-containing alloy in water to a particle size of from about 0.05 microns to about 100 microns, said alloy comprising, in atomic percent of the overall composition, of from about 12% to about 24% of at least one rare earth element, selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and the balance iron; b) compacting the crushed alloy material; c) drying the compacted alloy material at a temperature below the phase transformation temperature of the material; d) treating the compacted alloy material with a
  • steps a through d are the same as disclosed above for producing compacts.
  • the compacted alloy material is thereafter sintered and heat treated to produce permanent magnets, which have an increased Curie temperature as compared to a corresponding permanent magnet produced from a rare earth-containing alloy having the same overall composition only not treated with a passivating gas.
  • the resultant permanent magnet will have a nitrogen surface concentration of from about 0.4 to about 26.8 atomic percent and, preferably, 0.4 to 10.8 atomic percent.
  • the resultant permanent magnet When carbon dioxide is used as the passivating gas, the resultant permanent magnet will have a carbon surface concentration of from about 0.02 to about 15 atomic percent and, preferably, from 0.5 to 6.5 atomic percent. Of course, if a combination of nitrogen and carbon dioxide is used, the surface concentrations of the respective elements will be within the above-stated ranges.
  • the permanent magnets of this invention with a surface concentration of nitrogen have a higher Curie temperature than a corresponding magnet having the same overall composition with no surface concentration of nitrogen.
  • the permanent magnets of this invention with a surface concentration of carbon have a higher Curie temperature than a corresponding magnet having the same overall composition with no surface concentration of carbon.
  • the Curie temperature can be increased so that it is at least about 100°C higher than the Curie temperature of the corresponding magnets.
  • the Curie temperature can be maximized for a particular magnet composition in accordance with this invention.
  • Another preferred embodiment of the present invention includes an improved permanent magnet of the type comprised of, in atomic percent of the overall composition, from about 12% to about 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and at least 52% iron, wherein the improvement comprises a nitrogen surface concentration of from about 0.4 to about 26.8 atomic percent and, preferably, from 0.4 to 10.8 atomic percent.
  • This improved permanent magnet has a higher Curie temperature than a corresponding magnet having the same overall composition with no surface concentration of nitrogen.
  • the preferred rare earth element is neodymium and/or praseodymium.
  • the Curie temperature is at least 427°C, and it is believed that a Curie temperature of 500°C or more is possible pursuant to this invention.
  • a further preferred embodiment is an improved permanent magnet of the type comprised of, in atomic percent of the overall composition, from about 12% to about 24% of at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, from about 2% to about 28% boron and at least 52% iron, wherein the improvement comprises a carbon surface concentration of from about 0.02 to about 15 atomic percent and, preferably, 0.5 to 6.5 atomic percent.
  • This improved permanent magnet has a higher Curie temperature than a corresponding magnet having the same overall composition with no surface concentration of carbon.
  • the preferred rare earth element is also neodymium and/or praseodymium.
  • the Curie temperature is at least 461°C, and it is believed that a Curie temperature of 500°C or more is possible pursuant to this invention.
  • the present invention pertains to permanent magnets made from other suitable rare earth-containing alloys.
  • a further embodiment of the present invention includes an improved permanent magnet comprised of RM 5 or R 2 M 17 , wherein R is at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, and M is at least one metal selected from the group consisting of Co, Fe, Ni and Mn, wherein the improvement comprises the above-noted surface concentration of nitrogen.
  • R is at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium,
  • Another embodiment of the present invention includes an improved permanent magnet comprised of RM 5 or R 2 M 17 , wherein R is at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, ytterbium, lutetium, yttrium, and scandium, and M is at least one metal selected from the group consisting of Co, Fe, Ni and Mn, wherein the improvement comprises the above-noted surface concentration of carbon.
  • R is at least one rare earth element selected from the group consisting of neodymium, praseodymium, lanthanum, cerium, terbium, dysprosium, holmium, erbium, europium, samarium, gadolinium, promethium, thulium, y
  • the improved permanent magnets have a higher Curie temperature than a corresponding magnet having the same overall composition with no surface concentration of nitrogen or carbon.
  • the Curie temperature can be increased at least about 100°C higher than the Curie temperature of the corresponding magnet.
  • R is samarium and M is Co in the above embodiments, so the improved permanent magnet can be comprised of SmCo 5 or Sm 2 Co 17 .
  • the above embodiments can be comprised of Sm 2 Fe 17 .
  • the present invention is applicable to either anisotropic or isotropic permanent magnet materials, although isotropic materials have lower magnetic properties compared with the anisotropic materials.
  • the permanent magnets in accordance with the present invention have a high resistance to corrosion, highly developed magnetic and crystallographic texture, and high magnetic properties (coercive force, residual induction, and maximum energy product) , as well as increased Curie temperatures.
  • the examples set forth below are presented. The following examples are included as being illustrations of the invention and should not be construed as limiting the scope thereof.
  • FIGS. 1-11 illustrate the distribution of particle size and shape of powder for various weight ratios between powder and milling balls (P a /P b ) and grinding times.
  • the powder samples were oriented in a magnetic field and measurements were made on a plane perpendicular to the magnetic field.
  • FIGS. 1-11 show that the particle size and shape of powder produced in accordance with the present invention were optimized for compacting of the powder in a magnetic field to produce magnets since the number of desired rectangular shaped particles was maximized.
  • FIG. 12 illustrates a distribution of particle size and shape of Nd-Fe-B powder produced in accordance with the present invention and oriented in a magnetic field (H e ) as shown in the figure.
  • FIG. 13 illustrates Nd-Fe-B powder produced in accordance with the present invention wherein the nitrogen containing surface layer is visible.
  • FIG. 14 illustrates Nd-Fe-B powder produced by conventional powder metallurgy technique with the powder crushed in hexane and oriented in a magnetic field (H e ) as shown in the figure. Corrosion is evident in the conventional powder illustrated in FIG. 14.
  • FIG. 15 is an X-ray diffraction pattern of Nd-Fe-B powder produced in accordance with the present invention
  • FIG. 16 is an X-ray diffraction pattern of Nd-Fe-B powder produced by conventional powder metallurgy technique.
  • Comparison of FIG. 15 and FIG. 16 illustrates the difference in peak widths which indicates a higher defect density of domain wall pinning sites in the individual particles of the present invention.
  • Comparison of FIG. 15 and FIG. 16 also illustrates the difference in peak widths which indicates a higher density of defects that nucleate domains in the individual particles of the conventional powder, which adversely affect magnetic properties.
  • Powders and permanent magnets were prepared from the above-mentioned base composition in accordance with the present invention and the experimental parameters, including: the weight ratio between powder and milling balls (P a /P b ) , the length of time (T) the alloys were crushed in minutes, the typical particle size range of the powder after crushing (D ) in microns, and the temperature at which the powder was treated with the passivating gas (T ) in degrees centigrade, are given below in Table I. Nitrogen was used as the passivating gas for Samples 1, 4, 7 and 10. Carbon dioxide was used as the passivating gas for
  • Samples 2, 5, 8, and 11. A combination of nitrogen and carbon dioxide was used as the passivating gas for Samples 3, 6, 9 and 12.
  • Sample 13 is a prior art sample made by conventional methods for comparison.
  • FIG. 14 is a photomicrograph of Sample 13 and
  • FIG. 16 is an X-ray diffraction pattern of Sample 13. Each powder sample was compacted, sintered and heat treated. Magnetic properties were measured, and residual induction and maximum energy product were corrected for 100% density.
  • the magnetic properties included magnetic texture (A %-calculated) , average grain size in the sintered magnet (D Draw) , intrinsic coercive force H ci (kOe) , coercive force H c (kOe), residual induction B r (kG) , maximum energy product (BH) max (MGOe) , and corrosion activity.
  • the corrosion activity was measured visually after the samples had been exposed to 100% relative humidity for about two weeks (N - no corrosion observed, A - full corrosive activity observed, and S - slight corrosive activity observed) .
  • FIG. 17 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for Samples 1, 4, 7 and 10 having nitrogen surface concentrations in accordance with the present invention, and prior art Sample 13.
  • FIG. 17 is a graph showing the relationship between residual induction B r (kG) on the vertical axis and coercive force H c (kOe) as well as maximum energy product (BH) max (MGOe) on the horizontal axis for Samples 1, 4, 7 and 10 having nitrogen surface concentrations in accordance with the present invention, and prior art Sample 13.
  • FIG. 18 illustrates the relationship between B r (kG) on the vertical axis and H c (kOe) as well as (BH) max (MGOe) on the horizontal axis for Samples 2, 5, 8 and 11 having carbon surface concentrations in accordance with the present invention, and prior art Sample 13.
  • FIG. 19 illustrates the relationship between B r (kG) on the vertical axis and H c (kOe) as well as (BH) max (MGOe) on the horizontal axis for Samples 3, 6, 9 and 12 having both nitrogen and carbon surface concentrations in accordance with the present invention, and prior art Sample 13.
  • Permanent magnets were also made in accordance with this invention (Samples YB-1, YB-2 and YB-3) from powder having the following base composition in weight percent: Nd - 35.77%,
  • sintered permanent magnets of the Nd 2 Fe 14 B type were made in accordance with this invention (Samples D-l, D-2, D-3 and D-4) from alloy crushed in a passivating gas, the alloy having the following base composition in weight percent: Nd - 35.4%, B -1.2% and Fe - balance.
  • Sintered permanent magnets of the SmCo 5 type were also made in accordance with this invention (Samples D-5, D-6 and D-7) from alloy crushed in a passivating gas, the alloy having the following base composition in weight percent: S - 37% and Co - balance.
  • the alloy utilized was crushed in an attritor in a continuous flow of C0 2 for Samples D-1, D-2, D-3, D-5 and D-6, and N 2 for Samples D-4 and D-7, at a pressure of about 13.5 psig at ambient temperature to a particle size range of about 0.2 microns to 100 microns.
  • the powder was removed from the attritor, compacted without a protective atmosphere, and then sintered.
  • Samples D-5, D-6 and D- 7 were also annealed at 900°C for 1 hour.
  • the magnetic properties of all the sintered magnet samples would be enhanced by additional heat treatment as can be appreciated by those skilled in the art. The density and magnetic properties were measured and the results are reported in Table III below and FIGS. 24- 27.
  • sintered permanent magnets of the Nd 2 Fe 1 B type were made in accordance with this invention (Samples W-1, W-2, W-3 and W-4) from powder crushed in water, the powder having the following base composition in weight percent: Nd - 35.4%, B - 1.11% and Fe - balance.
  • Sintered permanent magnets of the SmCo 5 type were also made in accordance with this invention (Samples W-5, W-6 and W-7) from powder crushed in water, the powder having the following base composition in weight percent: Sm - 37% and Co - balance.
  • the powder utilized was wet compacted at a pressure of about 4 T/cm 2 .
  • the samples were placed in a vacuum furnace, the pressure was reduced to about 10 "5 Torr, and the samples were then heated to approximately 200°C for about 2 hours. The samples were then heated up from about 200°C to 760°C and, during this procedure, passivating gas was injected into the vacuum furnace chamber to passivate the compact samples when the temperature was from about
  • each compact sample was sintered and analyzed for magnetic properties.
  • the sintered magnet samples were not heat treated, but the magnetic properties of the samples would be enhanced by heat treatment after sintering as can be appreciated by those skilled in the art. The results are reported in Table IV below and FIGS. 28-31.
  • the Curie temperatures of permanent magnets made in accordance with this invention was also examined.
  • the permanent magnet samples were made from alloy crushed in water and dried to produce powder having the following base composition in weight percent: Nd - 35.4%, B - 1.2%, Dy - 1.3%, Pr - 0.4% and Fe - balance.
  • the powder for Samples C-l and N-1 was then treated with a passivating gas.
  • the powder for Sample C-l was heated in vacuum to about 175°C, treated with C0 2 , and allowed to cool.
  • the powder for Sample N-1 was heated in vacuum to about 225°C, treated with a combination of 92% N 2 and 8% C0 2 , and allowed to cool.
  • the powder was thereafter compacted and sintered in accordance with this invention.
  • the samples were made into a rectangular block and placed in a micro- vacuum furnace, which was then installed between the poles of the electromagnet of a VSM (Vibrating Sample Magnetometer) system.
  • the magnetization was measured in a direction that was parallel to the direction of easy magnetization of the samples.
  • the temperature was varied and the Curie temperature was calculated.
  • the Curie temperature of Sample A-l made by the conventional powder metallurgy technique was also determined for comparative purposes. The results are reported in Table V below.

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Abstract

Procédé de production d'une matière contenant des terres rares, pouvant être transformée en un aimant permanent ayant une température de Curie augmentée, consistant à traiter l'alliage à l'aide d'un gaz de passivation à une température inférieure à la température de transformation de phase de l'alliage, de manière à augmenter la température de Curie de la matière lorsque l'on transforme cette dernière en aimant permanent. On peut utiliser des alliages contenant des terres rares tels que des alliages Nd-Fe-B et Sm-Co. Le gaz de passivation peut être de l'azote, du dioxide de carbone ou une combinaison de ceux-ci. L'aimant permanent amélioré peut avoir une concentration d'azote en surface dont le pourcentage atomique est compris entre environ 0,4 et environ 26,8 si l'on utilise de l'azote comme gaz de passivation. L'aimant permanent amélioré peut également avoir une concentration de carbone en surface dont le pourcentage atomique est compris entre environ 0,02 et environ 15 si l'on utilise du dioxide de carbone comme gaz de passivation.
EP19910914184 1990-06-08 1990-12-12 Improved magnetic materials and process for producing the same Withdrawn EP0532701A4 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US07/535,460 US5122203A (en) 1989-06-13 1990-06-08 Magnetic materials
US535460 1990-06-08
PCT/US1990/003350 WO1990016075A1 (fr) 1989-06-13 1990-06-13 Matieres magnetiques ameliorees et procede pour leur production
WOPCT/US90/03350 1990-06-13

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AU2002309001B2 (en) * 2001-11-12 2008-08-07 George Anthony Contoleon Means of making wide pole face cobolt-rare earth magnets
TR201904655T4 (tr) 2008-03-12 2019-06-21 Ube Industries Piridilaminoasetik asit bileşiği.
CN114561585A (zh) * 2022-03-28 2022-05-31 广西大学 一种稀土掺杂软磁铁基合金粉末及其制备方法

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EP0532701A4 (en) 1993-07-14
WO1991019300A1 (fr) 1991-12-12

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