EP0466246B1 - Verfahren zum Herstellen eines isotropen dauermagnetischen Werkstoffs; isotroper dauermagnetischer Werkstoff und kunststoffgebundener isotroper Dauermagnet - Google Patents

Verfahren zum Herstellen eines isotropen dauermagnetischen Werkstoffs; isotroper dauermagnetischer Werkstoff und kunststoffgebundener isotroper Dauermagnet Download PDF

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Publication number
EP0466246B1
EP0466246B1 EP91201692A EP91201692A EP0466246B1 EP 0466246 B1 EP0466246 B1 EP 0466246B1 EP 91201692 A EP91201692 A EP 91201692A EP 91201692 A EP91201692 A EP 91201692A EP 0466246 B1 EP0466246 B1 EP 0466246B1
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EP
European Patent Office
Prior art keywords
isotropic
magnetic material
permanently magnetic
alloy
coercive force
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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.)
Expired - Lifetime
Application number
EP91201692A
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English (en)
French (fr)
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EP0466246A1 (de
Inventor
Dirk Bastiaan De Mooij
Henricus Arnoldus Antonius Keetels
John Eisses
Kurt Heinz Jürgen Buschow
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Koninklijke Philips NV
Original Assignee
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/058—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IVa elements, e.g. Gd2Fe14C

Definitions

  • the invention relates to a method of manufacturing an isotropic, permanently magnetic material which comprises Nd and/or Pr, Fe and C, the constituents of the material being melted together to form an alloy which is subsequently subjected to a thermal treatment, so that phase transformation takes place.
  • the invention also relates to an isotropic, permanently magnetic material and to a synthetic resin-bound isotropic permanent magnet.
  • a method of the type mentioned in the opening paragraph is known per se .
  • European Patent Application with publication number 320.064 a description is given of a method in which an alloy of Nd2Fe14C is subjected to a thermal treatment at 870°C for 500 hours to bring about a phase transformation.
  • the tetragonal "2-14-1" crystal structure is formed which is characteristic of the hard magnetic phase of the known Nd2Fe14B compound.
  • the thermal treatment must take place in a relatively small temperature range of 840°C to 890°C. Above 890°C, said tetragonal crystal structure is not formed. If the thermal treatment takes place at a temperature below 840°C, an impermissibly large quantity of Nd2Fe17 is formed in addition to the desired tetragonal phase.
  • the known method has disadvantages. It has been found that the magnetic material manufactured by said method has hardly any or no coercive force (H c ) after the phase transformation. The value of the coercive force is smaller than 50 kA/m. Due to said small coercive force the known material is not very suitable for use in synthetic resin-bound isotropic permanent magnets.
  • One of the objects of the invention is to improve the known method.
  • the invention is more particularly aimed at providing a method of manufacturing an isotropic, permanently magnetic material of the type mentioned in the opening paragraph, which material has coercive force.
  • the invention provides an isotropic, permanently magnetic material having a substantially single-phase crystal structure and a coercive force of at least 150 kA/m.
  • the magnetic material should further have a high saturation magnetization.
  • a further object of the invention is to provide a synthetic resin-bound isotropic permanent magnet.
  • the alloy comprises 10-20 at.% of Nd and/or Pr, 70-85 at.% of Fe, 4-11 at.% of C and 0.1-2 at.% of B, and in that the thermal treatment takes place at a temperature between 900°C and 1050°C.
  • the invention is based on, inter alia, the experimentally gained insight that the temperature range in which phase transformation takes place can be considerably extended by substituting a small quantity of C of the known Nd2Fe14C by B.
  • phase transformation only takes place in the range from 840°C to 890°C, yet in the case of the material according to the invention the formation of the tetragonal phase takes place in the temperature range from 800 to 1050°C.
  • the thermal treatment is carried out at 900-1050°C, the material exhibits a coercive force of at least 150 kA/m.
  • the rare earth metal content in the alloy should consist exclusively or almost exclusively of Nd and/or Pr. This provides the magnetic material according to the inventive method with a high saturation magnetization. A small quantity of other rare earth metals (up to 10 at.%) may be suitable to influence certain magnetic properties of the material. Preferably, however, the material comprises only Nd as the rare earth metal. In this manner, the highest saturation magnetization is attained.
  • the isotropic, permanently magnetic material obtained according to the inventive method comprises exclusively or substantially exclusively Fe as the transition metal. Under certain conditions it might be advantageous for the material to also comprise a small quantity of Co as the transition metal (up to 10 at.%). Co increases the Curie temperature and the corrosion resistance of the magnetic material. Co-containing magnets can moreover be oriented at much smaller fields than magnets containing only Fe as the transition metal. In the case of the latter magnets, fields of at least 5 T are required. Co-containing magnets can already be optimally oriented at 2.0 T. If, however, a maximum saturation magnetization is aimed at, only Fe is to be used as the transition metal.
  • B takes up the lattice site of C in the crystallized "Nd2Fe14C"-structure.
  • the molar quantity of B is at least 2.5 % of the overall content of B and C.
  • the molar quantity of B is maximally 15 % of the overall content of B and C.
  • recrystallization results in multiphase material being formed. This is regarded as a disadvantage.
  • R2Fe14CxB 1-x -compounds are known from Fig. 1 of J. Appl. Phys. 61 3574 (1987).
  • R denotes a rare earth metal.
  • a range is indicated in which the Fe77R15(B, C)8-compounds form a continuous series.
  • compositions which comprise only Nd as the rare earth metal and which, in addition to C comprise a small quantity of B. These compounds, however, have been subjected to a thermal treatment at 800°C and, consequently, have no appreciable coercive force.
  • An interesting embodiment of the method according to the invention is characterized in that the alloy is subjected to the thermal treatment for maximally 4 days.
  • a heat treatment of at least approximately one week is necessary to bring about the desired tetragonal crystal structure in the alloy. With a view to an economical production, such long thermal treatments are undesirable.
  • a further advantageous embodiment of the method according to the invention is characterized in that the alloy is ground to form a magnetic powder having an average particle size of 2 to 40 »m. It has been found that the coercive force of the magnetic material increases considerably when, following the thermal treatment, the alloy is ground to form a magnetic powder having an average particle size of 2-40 »m.
  • the grinding operation is carried out in, for example, a ball mill. After grinding, magnetic powders are obtained having a H c of at least 500 kA/m.
  • the invention further relates to an isotropic permanently magnetic material.
  • said material is characterized in that it comprises 10-20 at.% of Nd and/or Pr, 70-85 at.% of Fe, 4-11 at.% of C and 0.1-2 at.% of B, and in that the material has a coercive force of at least 150 kA/m.
  • Said material is preferably powderous and has an average particle size of 2-40 »m and a coercive force of at least 500 kA/m. Such a powder can be advantageously used in a synthetic resin-bound, isotropic, permanent magnet.
  • the invention further relates to a synthetic resin-bound, isotropic, permanent magnet.
  • said magnet is characterized in that it comprises an isotropic, permanently magnetic material which is composed of 10-20 at.% of Nd and/or Pr, 70-85 at.% of Fe, 4-11 at.% of C and 0.1-2 at.% B, and which is powderous with an average particle size in the range between 2 and 40 »m, and in that the material has a coercive force of at least 500 kA/m.
  • Fig. 1 shows the maximum temperature T(°C) at which the isotropic, magnetic material Nd2Fe14C 1-x B x or Pr2Fe14C 1-x B x can be formed as a function of the B-content x.
  • Fig. 2 shows the effect of the grinding time t(min.) on the coercive force H c (kA/m) of an alloy of composition Nd15Fe77C 7.68 B 0.32 .
  • Fig. 3 shows a hysteresis loop of a magnetic alloy of the composition Nd16Fe75C 8.55 B 0.45 .
  • a number of alloys comprising 10-20 at.% of Nd and/or Pr, 70-85 at.% of Fe, 4-11 at.% of C and 0.1-2 at.% of B was manufactured.
  • a mixture of the constituents in the desired ratio was melted together by means of an arc at approximately 1800°C.
  • the alloys were subsequently sealed into glass capsules under a vacuum and then subjected to a thermal treatment to bring about phase transformation. The duration and the temperature of the thermal treatment were varied. X-ray analysis showed that the crystallized alloys were substantially completely single-phase and exhibited a tetragonal structure. The coercive force of the unground alloys was determined.
  • the alloys were subsequently ground in a ball mill, under an inert atmosphere (nitrogen or vacuum), to form a powder having an average particle size ranging between 2 and 40 »m.
  • the variation of the H c as a function of the grinding duration was investigated.
  • the ground powders were fixed in a synthetic resin.
  • the powder particles were oriented by means of a magnetic field.
  • the alloys 1-9 were oriented using a field of 5 T.
  • the alloys 10-12 were oriented using a field of 2.0 T.
  • the H c of these magnets was measured by means of a vibrating sample magnetometer.
  • the Table shows a number of compositions and properties of the alloys which were manufactured by the method according to the invention.
  • Column 1 lists the number of the exemplary embodiment.
  • Column 2 lists the composition of the alloys.
  • the duration (days) and the temperature (°C) of the thermal treatment are listed in column 3 and column 4, respectively.
  • the coercive force (kA/m) of the recrystallized alloy before and after the grinding operation are listed in column 5 and column 6, respectively.
  • the grinding operation took place in a ball mill for 10-20 minutes, until an average grain size was attained which ranges between 2 and 40 »m.
  • Column 7 lists the saturation magnetization (emu/g) of the synthetic resin-bound isotropic permanent magnets obtained by fixing the powder in wax.
  • the energy product B.H max of the magnets based on alloys 10-12 was approximately 70 kJ/m3.
  • Fig. 1 shows the effect of a small substitution of C by B in Nd2Fe14C on the maximum transformation temperature. Above the line shown, the intended tetragonal phase is not achieved. When approximately 2.5% of B is added, related to the overall content of C and B, it is found that the maximum transformation temperature has risen from 890°C to 1050°C.
  • Fig. 2 shows the effect of grinding (duration t in min.) on the coercive force (H c , kA/m) of an alloy obtained according to the inventive method (exemplary embodiment 2).
  • the grinding operation almost tripled the coercive force.
  • the Figure further shows that too long a grinding treatment adversely affects the coercive force of the powder.
  • Fig. 3 shows the hysteresis loop of a magnetic alloy having the composition Nd16Fe75C 8.55 B 0.45 at a magnetic field of 5 T.
  • the alloy was heated at 950°C for 1 day.
  • the remanence was 0.65 T.

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  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Hard Magnetic Materials (AREA)

Claims (6)

  1. Verfahren zum Herstellen eines isotropen, dauermagnetischen Werkstoffs, der Nd und/oder Pr, Fe und C enthält, wobei die bestandteile des Werkstoffs zu einer Legierung zerschmolzen werden, die danach einer Wärmebehandlung ausgesetzt wird, so daß Phasentransformation auftritt, dadurch gekennzeichnet, daß die Legierung 10-20 at. % Nd und/oder Pr, 70-85 at. % Fe, 4-11 at. % C und 0,1-2 at. % B aufweist, und daß die thermische behandlung bei einer Temperatur zwischen 900°C und 1050°C erfolgt.
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Legierung maximal 4 Tage lang der thermischen Behandlung ausgesetzt wird.
  3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Legierung zu einem Magnetpulver mit einer mittleren Teilchengröße von 2 bis 40 »m zermahlen wird.
  4. Isotroper dauermagnetischer Werkstoff, dadurch gekennzeichnet, daß er 10-20 at. % Nd und/oder Pr, 70-85 at. % Fe, 4-11 at. % C und 0,1-2 at. % B aufweist, und daß der Werkstoff eine Koerzitivkraft von mindestens 150 kA/m hat.
  5. Isotroper dauermagnetischer Werkstoff nach Anspruch 4, dadurch gekennzeichnet, daß er ebenfalls Co in einer Menge von maximal 10 at. % enthält.
  6. Kunststoffgebundener isotroper Dauermagnet, dadurch gekennzeichnet, daß er einen isotropen, dauermagnetischen Werkstoff nach Anspruch 4 oder 5 enthält.
EP91201692A 1990-07-09 1991-07-02 Verfahren zum Herstellen eines isotropen dauermagnetischen Werkstoffs; isotroper dauermagnetischer Werkstoff und kunststoffgebundener isotroper Dauermagnet Expired - Lifetime EP0466246B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL9001561 1990-07-09
NL9001561 1990-07-09

Publications (2)

Publication Number Publication Date
EP0466246A1 EP0466246A1 (de) 1992-01-15
EP0466246B1 true EP0466246B1 (de) 1994-09-28

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EP91201692A Expired - Lifetime EP0466246B1 (de) 1990-07-09 1991-07-02 Verfahren zum Herstellen eines isotropen dauermagnetischen Werkstoffs; isotroper dauermagnetischer Werkstoff und kunststoffgebundener isotroper Dauermagnet

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EP (1) EP0466246B1 (de)
JP (1) JPH04233201A (de)
CN (1) CN1059618A (de)
DE (1) DE69104284D1 (de)

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4849035A (en) * 1987-08-11 1989-07-18 Crucible Materials Corporation Rare earth, iron carbon permanent magnet alloys and method for producing the same

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
308; F.Bolzoni et Al.: "MAGNETIC ANISOTROPY OF CARBON DOPED Nd2Fe14B" *

Also Published As

Publication number Publication date
DE69104284D1 (de) 1994-11-03
JPH04233201A (ja) 1992-08-21
EP0466246A1 (de) 1992-01-15
CN1059618A (zh) 1992-03-18

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