GB2238797A - Manufacture of rare-earth materials and permanent magnets - Google Patents

Manufacture of rare-earth materials and permanent magnets Download PDF

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Publication number
GB2238797A
GB2238797A GB8927826A GB8927826A GB2238797A GB 2238797 A GB2238797 A GB 2238797A GB 8927826 A GB8927826 A GB 8927826A GB 8927826 A GB8927826 A GB 8927826A GB 2238797 A GB2238797 A GB 2238797A
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United Kingdom
Prior art keywords
alloy
rare
compound
earth
magnet
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.)
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Application number
GB8927826A
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GB8927826D0 (en
Inventor
Ewoud Rozendaal
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Philips Electronics UK Ltd
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Philips Electronic and Associated Industries Ltd
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Publication date
Application filed by Philips Electronic and Associated Industries Ltd filed Critical Philips Electronic and Associated Industries Ltd
Priority to GB8927826A priority Critical patent/GB2238797A/en
Publication of GB8927826D0 publication Critical patent/GB8927826D0/en
Publication of GB2238797A publication Critical patent/GB2238797A/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Withdrawn legal-status Critical Current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
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • C22C1/058—Mixtures of metal powder with non-metallic powder by reaction sintering (i.e. gasless reaction starting from a mixture of solid metal compounds)
    • 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
    • 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

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Power Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Hard Magnetic Materials (AREA)
  • Manufacturing Cores, Coils, And Magnets (AREA)

Abstract

Sintered and other rare-earth permanent magnets are manufactured from an alloy material comprising FE and at least one element of the rare-earth metal group (including yttrium), for example a Fe-B-R alloy. At least one coercivity-increasing additional element such as Al is incorporated in the material via ferro-boron, or as a boride, or as another ferro-compound. The material may be formed by the steps of (a) forming a compound comprising Al and Fe by an alumino-thermic reduction process using excess Al and (b) adding the Al-Fe compound as a constituent of the alloy so as to incorporate the Al into the alloy material.

Description

DESCRIPTION MANUFACTURE OF RARE-EARTH ALLOY MATERIALS AND PERMANENT MAGNETS.
This invention relates to methods of manufacturing rare-earth alloy permanent magnets and alloy materials for such magnets, particularly but not exclusively materials of the Fe-B-R alloy type where R is at least one element of the rare-earth metal group (inclusive of yttrium). The invention also relates to such alloy materials and to permanent magnets comprising such materials.
Magnetic materials based on Fe-B-R type intermetallic compounds with tetragonal crystal structure have been used to manufacture permanent magnets having coercive fields of considerable magnitude, for example about 1000 kA.m~l and more. It is known from, for example, published European patent application EP-A-O 101 552 that the coercivity of magnets of the Fe-B-R type can be increased by inclusion of at least one additional element M in the alloy composition, where M includes Ti,Ni,Bi,V,Nb,Ta,Cr,Mo, W,Mn,Al,Sb,Ge,Sn,Zr and Hf. The resulting alloy material may be designated as being of the Fe-B-R-M type. The whole contents of EP-A-O 101 552 are hereby incorporated herein as reference material.
As described in EP-A-O 101 552, these additional elements M are added to the melt-constituents for the alloy as very pure elements in most cases. Thus, for example, in order to incorporate Al, aluminium having a purity of 99.9% is added. However, it is suggested in the cases of V,Nb,Cr and Zr to incorporate these elements by adding ferrovanadium, ferroniobium, ferrochromium and ferrozirconium respectively. Among others, W,Mo,V,Al and Nb have a great effect in increasing coercivity IHc, and Al is especially convenient as being an inexpensive material. This increase in IHc due to the addition of one or more elements M results in increased stability and wide applicability of the magnets, as mentioned in EP-A-O 101 552.However, the addition of M reduces the remanence Br of the magnet; the greater the amount of M, the lower becomes the value of Br, and Br may be as much as halved as described in EP-A-O 101 552 by adding, for example, upto between 8 and 12 atomic percent of particular elements M. The addition of one or more of these elements M in this manner does not seem to increase greatly the upper limit for the temperature range to which the resulting magnets can be reliably subjected in their application use.
The application temperature for magnets of the Fe-B-R type can be increased by incorporating dysprosium as part of the rare-earth (R) constituent. Thus, for example, for a Fe-B-Nd type magnet with no Dy content, the recommended maximum operating temperature for the magnet may be about 800C (degrees Celsius). This maximum temperature can be increased to about 1100C by adding about 40k ppm of Dy to the alloy, and to about 1500C by adding about 60k ppm of Dy. The addition of Dy slightly reduces the remanence Br of the magnet, for example by about 5% for 40k ppm of Dy and by a further 5% (total 10% reduction) for 60k ppm of Dy. More importantly however, Dy is a very expensive rare-earth element and so the addition of Dy to increase the application temperature of the magnet increases significantly the manufacturing cost of the magnet.
The present invention provides methods of manufacturing rare-earth alloy materials, and permanent magnets comprising such materials, in which at least one additional element M is incorporated in the alloy material but in a different manner from that described in EP-A-O 101 552 and such that (a) a higher increase in coercivity may be obtained, (b) any decrease in remanence may be reduced, and/or (c) the maximum application temperature may be increased without needing to add any significant amount of an expensive extra rare-earth element such as Dy.
According to one aspect of the present invention a method of manufacturing a Fe-B-R rare-earth alloy permanent-magnet material is characterised by the incorporation in the alloy material of at least one coercivity-increasing additional element M via Fe-B.
Thus, as a constituent in the alloy preparation, a compound of the element M with ferroboron may be added.
According to another aspect of the present invention a method of manufacturing a Fe-B-R rare-earth alloy permanent-magnet material is characterised by the incorporation in the alloy material of at least one coercivity-increasing additional element M (at least in part) as a boride of M.
In one particular example in accordance with the invention, the element M is aluminium which is relatively inexpensive material. The Al may be incorporated at least in part as aluminium boride, for a Fe-B-R type magnet. In the manufacture of a Fe-B-R type alloy material the Fe-B may be added as ferroboron obtained by an alumino-thermic reduction process, and in this case excess aluminium may be used in the reduction process so that a FeB(Al) compound is used as a constituent of the alloy, thereby incorporating the Al in the alloy.
According to a further aspect of the present invention a method of manufacturing a permanent-magnet alloy material comprising Fe and at least one element of the rare-earth metal group (including yttrium) is characterised by the steps of (a) forming a compound comprising Al and Fe by an alumino-thermic reduction process using excess Al and (b) adding the Al-Fe compound as a constituent of the alloy so as to incorporate the Al into the alloy material.
Rare-earth alloy permanent-magnet materials comprising at least one additional element M incorporated in accordance with the present invention may be further processed in known manner to form desired magnet bodies, for example as described in EP-A-O 101 552 and in the paper entitled "The physical metallurgy and processing of sintered rare-earth permenanet magnets" by Dr. J. Ormerod in Journal of the Less Common Metals Vol. 111 (1985) pages 49 to 69, published by Elsevier Sequoia S.A., Lausanne, the whole contents of which are hereby incorporated herein as reference material. Other background information is contained in the book edited by I.V. Mitchell, entitled "Nd-Fe Permanent Magnets: Their Present and Future Applications", published by Elsevier Applied Science Publishers, London and New York and the whole contents of which are also hereby incorporated herein.This book contains a report and proceedings of a Workshop held in Brussels on 25th October 1984.
Aluminium or at least one other coercivity-improving additional element M may be incorporated in accordance with the present invention in various rare-earth alloy materials, for example a material of which at least 50 volume percent is of a Fe-B-R type tetragonal crystal structure and comprising at least 42 atomic percent of Fe, 2 to 28 atomic percent of B and 10 to 30 atomic of R where R is at least one rare-earth element selected from the group consisting of Nd,Pr,Dy,Ho and Tb, or a mixture of said at least one element and at least one selected from the group consisting of La,Ce,Sm,Gd,Er,Eu,Tm,Yb,Lu,Pm and Y. Of the rare-earth elements listed, preferably the expensive ones (such as Dy) are avoided.Popular and less expensive rare-earth alloy materials for which the invention may be used are of the Nd-Fe-B type, and a specific example of such an Nd-Fe-B alloy will now be described with reference to the accompanying drawing to illustrate features in accordance with the present invention.
The results of Figure 1 were obtained with permanent magnets whose basic composition is Ndl6Fe76Bg. Several alloys were prepared using vacuum induction melting and with a range of Al constituent up to 0.6% by weight. Figure 1 is a plot of coercivity IHc in kA.m~1 against Al content in ppm of Al by weight in the alloy for two methods of incorporating the Al, namely doping the melt with (a) pure Al and (b) via ferroboron produced by an alumino-thermic reduction process using excess Al. The density of the magnet bodies was in the range 7.4 to 7.5 gm.cm 3.
The alloys were simultaneously processed into sintered magnets using known production process steps, including hydrogen decrepitation of the cast material, jet milling, pressing, vacuum sintering, heat-treating, machining and testing. The Nd/Fe ratios of all castings were determined using X-ray fluorescence, and the Al contents were determined using atomic absorption analysis. The sintered magnets were characterised by density and magnetic property measurements.
As can be seen by comparing curves (a) and (b) in Figure 1, a significantly higher increase of IHc of the sintered magnets is observed by Al doping via the Fe-B rather than by doping with pure Al. Thus, adding 0.25% Al by weight (2500 ppm) to the alloy via the Fe-B resulted in a 20% increase of IHc over doping with pure Al. This magnitude of increase in IHc permits the design of higher operating temperature magnets with Al incorporated in accordance with the invention and without needing the addition of expensive Dy. The addition of Al in this manner via the Fe-R does reduce the remanence Br, but the reduction in remanence is less than 3% for 0.3% Al (3000 ppm).
A satisfactory explanation of this surprising increase in coercivity is not clear at present, but the Al incorporated in accordance with the present invention seems to result in changes in bulk and/or grain boundary morphologies and composition. The Al may be at least in part in the form of aluminium boride, but a compound phase with the iron may be present. The ferroboron which is added to the melt is formed by an alumino-thermic reduction process in which the aluminium reduces oxides of iron and boron to produce ferroboron and alumina. By using excess Al for this alumino-thermic reduction process, the desired excess Al content is incorporated in the ferroboron. The alumina is separated off, and the remaining FeB(Al) composition is added to the alloy melt comprising 99.9% pure Fe and 95% pure Nd to incorporate the desired Al level in accordance with the present invention.
From reading the present disclosure, many modifications and variations will be apparent to persons skilled in the art. Such modifications and variations may involve other features which are already known in the design, manufacture and use of rare-earth magnet alloys and which may be used instead of or in addition to features already described herein. Although Fe-B-R type alloys have been described, rare-earth magnets may also be made with Fe-C-R type alloys (where C is carbon) and these may incorporate Al or other elements M in accordance with the invention. Magnesium and/or calcium may be used instead of (or in addition to) Al, to produce the ferroboron by a thermal reduction of the oxides of iron and boron.
Although reference has been made to particular combinations of process and compositional features, it should be understood that the scope of the disclosure of the present application also includes any one of the novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that claims may be formulated to any such features and/or any combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims (6)

CLAIM(S)
1. A method of manufacturing a Fe-B-R rare-earth alloy permanent-magnet material, characterised by the incorporation in the alloy material of at least one coercivity-increasing additional element M via Fe-B.
2. A method as claimed in claim 1, further characterised in that as a constituent in the alloy preparation, a compound of the element M with ferroboron is added.
3. A method of manufacturing a Fe-B-R rare-earth alloy permanent-magnet material, characterised by the incorporation in the alloy material of at least one coercivity-increasing additional element M at least in part as a boride of M.
4. A method as claimed in any of the preceding claims, further characterised in that the element M is aluminium.
5. A method as claimed in claim 4, further characterised in that the alloy material comprises ferroboron obtained by an alumino-thermic reduction process, and in that excess aluminium is used in the reduction process so that a FeB(A1) compound is added as a constituent of the alloy, thereby incorporating the Al in the alloy.
6. A method of manufacturing a permanent-magnet alloy material comprising Fe and at least one element of the rare-earth metal group (including yttrium), characterised by the steps of (a) forming a compound comprising Al and Fe by an alumino-thermic reduction process using excess Al and (b) adding the Al-Fe compound as a constituent of the alloy so as to incorporate the Al into the alloy material.
GB8927826A 1989-12-08 1989-12-08 Manufacture of rare-earth materials and permanent magnets Withdrawn GB2238797A (en)

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Application Number Priority Date Filing Date Title
GB8927826A GB2238797A (en) 1989-12-08 1989-12-08 Manufacture of rare-earth materials and permanent magnets

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GB2238797A true GB2238797A (en) 1991-06-12

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4612047A (en) * 1985-10-28 1986-09-16 The United States Of America As Represented By The United States Department Of Energy Preparations of rare earth-iron alloys by thermite reduction
US4769063A (en) * 1986-03-06 1988-09-06 Sumitomo Special Metals Co., Ltd. Method for producing rare earth alloy
US4837109A (en) * 1986-07-21 1989-06-06 Hitachi Metals, Ltd. Method of producing neodymium-iron-boron permanent magnet
EP0101552B1 (en) * 1982-08-21 1989-08-09 Sumitomo Special Metals Co., Ltd. Magnetic materials, permanent magnets and methods of making those

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0101552B1 (en) * 1982-08-21 1989-08-09 Sumitomo Special Metals Co., Ltd. Magnetic materials, permanent magnets and methods of making those
US4612047A (en) * 1985-10-28 1986-09-16 The United States Of America As Represented By The United States Department Of Energy Preparations of rare earth-iron alloys by thermite reduction
US4769063A (en) * 1986-03-06 1988-09-06 Sumitomo Special Metals Co., Ltd. Method for producing rare earth alloy
US4837109A (en) * 1986-07-21 1989-06-06 Hitachi Metals, Ltd. Method of producing neodymium-iron-boron permanent magnet

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GB8927826D0 (en) 1990-02-14

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