GB2419602A - Magnetic alloy of the RE2TM14B type and a method of making magnetic alloys - Google Patents
Magnetic alloy of the RE2TM14B type and a method of making magnetic alloys Download PDFInfo
- Publication number
- GB2419602A GB2419602A GB0521804A GB0521804A GB2419602A GB 2419602 A GB2419602 A GB 2419602A GB 0521804 A GB0521804 A GB 0521804A GB 0521804 A GB0521804 A GB 0521804A GB 2419602 A GB2419602 A GB 2419602A
- Authority
- GB
- United Kingdom
- Prior art keywords
- alloy
- boron
- rare earth
- zirconium
- iron
- 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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Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- 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
Abstract
A magnetic alloy comprises (in atomic %): 11.8-15.0 % rare earth metals, 77.0-82.0 % transition metals, 5.3-9.0 % boron and up to 2.0 % of titanium, zirconium, hafnium or a mixture thereof. A claimed alloy comprises (in atomic %): about 13.0 % neodymium, about 77.5 % iron, about 8.6 % boron and about 1.0 % zirconium. Also a method of making a rare earth-iron-boron alloy where at least one Group IVB transition metal (Ti, Zr, Hf) is added during melting and casting of the alloy.
Description
IRON CONTAINING RARE EARTH-TRANSITION METAL-BORON TYPE
ALLOYS WITH REDUCED FREE IRON PHASE AND METHODS FOR
PRODUCTION THEREOF
Field of Invention
The present invention relates to the manufacture of rare earth-transition metal-boron alloys, mainly for use in the production of high performance permanent magnets. More specifically, the present invention relates to a method of improving the suitability of such alloys for use in permanent magnets.
Background of the Invention
The use of magnets has been common place for over 200 years and is widespread throughout a large number of industries. However the development of high performance permanent magnets has been a more recent phenomenon, and has been a major driving force behind the modern electronics industry.
High performance permanent magnets are typically made from rare earthtransition metal alloys that rely on control of composition and microstructure for their magnetic properties. One of the most commonly used alloys of this type is the rare earth-iron-boron type alloy.
Permanent magnet materials based on rare earth metals, transition metals and boron as alloys have properties dependent upon their composition and microstructure. The power of this kind of magnet (i.e. its energy product) is enhanced by achieving the maximum amount of active ferromagnetic phase in the magnet microstructure; this optimum phase is composed of rare earth (2 atomic proportions of one or more rare earth metals, usually neodymium) , transition metal (14 atomic proportions of one or more transitional metals, usually iron and cobalt) and boron (1 atomic proportion): RE2TMI4B.
A more detailed discussion of the science involved in these types of permanent magnets can be found in 0. Brown, B-M. Ma and Z. Chen.
"Developments in the Processing and Properties of NdFeB-type Permanent Magnets". J. Magnetism and Magnetic materials 248(2002) 432-440.
Casting of an alloy at the atomic ratio required for optimum magnetic properties results in an imperfect microstructure consisting of RE2TMI4B phase, a rare earth rich phase and a free iron phase.
During the production of an alloy, the desired compositions for a permanent magnet are not always easily produced by melting and casting alone. This is because the ferromagnetic crystals that confer the highest performance in magnets (i.e. the RE2TMI4B phase) do not form directly on solidification from molten alloys. When casting a high performance alloy the solidification process starts with formation of iron dendrites (i.e. free iron) and ends with solidification of a rare earth rich mixture.
The presence of the free iron dendrites and the rare earth rich phase are both deleterious to the performance of permanent magnets made from rare earth-transition metal alloys.
The presence of free iron badly affects the retention of permanent magnet properties. This is because iron is a "soft" magnetic phase and its presence in a permanent magnet decreases the property of the magnet to resist loss of magnet strength.
The presence of the rare earth rich phase causes increased rates of corrosion and dilutes the proportion of the desired ferromagnetic crystals in the microstructure.
At present, in order to overcome these microstructural problems and to make alloys suitable for the production of permanent magnets, the cast alloys have to be heat treated to dissolve the free iron. Such a method is time consuming (sometimes taking several days) and costly, due to the high energy requirements.
In an alternative treatment method the alloys are cast under special chilled conditions to suppress the formation of free iron. Once again, the processing costs involved in this method are prohibitive.
A more detailed discussion of the problems caused by the free iron phase and the rare earth rich phase, together with an outline of the various techniques currently used to address such problems, can be found in 0.
Gutfleisch. "Controlling the Properties of High Energy Density Permanent Magnetic Materials by Different Processing Routes". J. AppI. Phys. 33(2000) R157-R172.
Statement of Invention
In view of the above identified problems, the present invention provides a magnetic alloy according to claim 1.
Preferably the alloy may comprise 12.0 - 14.5 atomic% rare earth metal. Preferably the alloy may comprise 0.3 -1.3 atomic% IVB transitional metal. Preferably the alloy may comprise 5.9 -8.9 atomic% boron.
The present invention also provides a method of producing a rare earthtransition metal-boron type alloy with a reduced free iron phase content, wherein the transition metal component of the alloy comprises iron, whereby at least one group IVB transition metal is added to the alloy mixture during the melting and casting of the alloy.
Of the potential group IVB transition metals available(viz., titanium, zirconium and hafnium), zirconium is the most preferable for the present invention. However, it is appreciated that any of the group IVB transition metals, whether in combination or alone, could be used in the method of the present invention.
Preferably, the amount of zirconium added to the alloy mixture is not more than 3% of the total weight of the alloy mixture, which is approximately 2.1 atomic%. Further preferably, the amount added is not more than 2% of the total weight, which is approximately 1.4 atomic%.
Advantageously, an additional amount of boron may also be added to the alloy mixture. The amount of additional boron added should preferably be provided in an atomic proportion of 2:1 with the group IVB transition metal additive. Preferably such an additional amount should not be more than 1% of the total weight of the alloy mixture, which is approximately 5.9 atomic %.
The boron and the group IVB transition metal may preferably be added to the alloy mixture in the form of ZrB2.
Preferably, the rare earth component of the alloy may be provided by at least one metal selected from the group containing: praseodymium; neodymium; dysprosium; and terbium.
Preferably, the transition metal component of the alloy also comprises at least one further metal selected from the group containing: cobalt; nickel; copper; and zinc.
Further aspects of the present invention relate to the alloys produced by the above method and to permanent magnets produced from such alloys.
It is appreciated that addition of zirconium (or an alternative group IVB transition metal), with additional boron, has the effect of reducing free iron precipitates and rare earth rich and boron rich phases in cast RE2TMI4B type alloys, which has the effect of improving permanent magnets made from these alloys by removing the need for heat treatment of cast alloys before magnet production and also improves the corrosion resistance of permanent magnets made with these alloys.
It will be appreciated that although the present application mostly discusses zirconium, the similar characteristics of other group IVB transition metals such as titanium and hafnium makes them interchangeable for the purposes of the present invention. It is also considered that more than one group IVB transition metal could be used in the alloy of the present invention.
Zirconium added alone to cast rare earth, transition metal, boron-type alloys will reduce free-iron in additions of up to 0.8 atomic %.
Zirconium added in combination with additional boron to cast rare earth, transition metal, boron-type alloys, will almost completely suppress the free iron content in additions of up to I total weight%, which is approximately 5.9 atomic%.
Zirconium added in combination with additional boron to cast rare earth, transition metal, boron-type alloys, increases the volume fraction of the desired permanent magnet phase RE2TMI4B in additions of up to 2 atomic %.
It is understood that the addition of zirconium changes the kinetics of alloy reactions with hydrogen (commonly used in processes to form magnetic products), allowing easier inducement of magnetic anisotropy resulting in improved energy product of rare earth, transition metal, boron-type permanent magnet alloys.
Furthermore, the addition of zirconium, or zirconium and boron, also results in improved corrosion resistance of RE2TMI4B type magnetic materials by reducing the quantity of the rare earth rich phase and the boron rich phase precipitates in the alloy.
Yet further, the addition of boron, in conjunction with zirconium, has the affect of preventing the precipitation of RE2TMI7 phases, which are a major problem due to their "soft" magnetic nature and serious influence on the permanent magnetic properties.
The advantages of a cast RE2TMi4B-type alloy with little or no free iron, rare earth and boron rich phases are to remove the need for heat treatment of cast alloys prior to their use in permanent magnet production and to improve corrosion resistance of magnet products made from these alloys.
Brief Description of the Drawings
In the drawings, which show experimental data relating to the alloys of the present invention: Figure 1 Illustrates the section through the ternary phase diagram Nd- Fe-B that is shown in Figure 2; Figure 2 shows the phase diagram of iron versus neodymium/boron (ratio 2/1); Figure 3 shows graphically the results of adding zirconium to a rare earth-transition metal-boron type alloy of composition Nd1298, Fe8o.4, B6.56, Zr; and Figure 4 shows graphically the results of adding zirconium, in combination with boron, to a rare earth-transition metal- boron type alloy of composition Nd12.98, Fe80 46-3x, B6 + , Zr.
Detailed Description of the Invention
Alloys for high energy permanent magnets have been made by melting raw materials such as neodymium, iron and boron (boron supplied in the form of ferro-boron master alloy) in an inert atmosphere (to prevent oxidation) .
These alloys are cast into simple flat plates (commonly known as "bookmould" casting). This alloy product is then further processed into permanent magnets by a variety of methods involving heat treatment, crushing to fine powder, use of hydrogen and sintering. Once again see the Gutfleisch reference for a technical review of the types of alloys and methods of magnet production.
The precise compositions of the cast alloys are selected according to the properties of the magnets that will be made from the cast alloy. In some cases the selected alloy composition causes a significant proportion of free- iron to form in the cast alloy microstructure. It is necessary to heat treat these alloys to reduce or eliminate free iron in the microstructure, which also has the effect of reducing the quantity of the rare earth and boron rich phase precipitates as the metals diffuse and reform as RE2TMi4B-type phases.
In the composition of alloys, the rare earth (RE) component is generally neodymium that may be part substituted with other rare earth metals such as praseodymium, dysprosium, terbium (although other rare earth metals are also considered viable). The transition metal (TM) component is generally iron, which may be part substituted with cobalt and other transition metals.
The principal of making zirconium (or other group IVB metals) additions, and these additions in association with boron, to improve alloy microstructure applies whichever of these rare earth or transition metals is present in substitution of Nd or Fe in the crystal structure.
By using small additions of zirconium, or zirconium and boron, to the melting process we have shown that precipitation of free-iron during the casting of rare earth-iron-boron type alloys can be much reduced or even eliminated.
Figure 2 shows a pseudo-binary phase diagram for Iron (Fe) versus Neodymium (Nd) and Boron (B) in an atomic ratio of 2 Neodymium atoms: I Boron atom. The diagram shows that if a liquid mixture of NdFeB (labelled "L") is made with the composition of the permanent magnet phase RE2TMI4B (also shown as cD) then the first material to solidify will be Fe as we are in the field of Liquid + Fe. As the liquid cools the next material to solidify is RE2TMI4B leaving a proportion of liquid that is rich in Nd and B, liquid will be of composition "X". The proportion of rare earth and boron rich liquid will be in proportion to the amount of iron that precipitated during the cooling process.
The symbol q represents the RE(Fe4B4) phase that solidifies on grain boundaries with the RE-rich (shown as Nd) phase, which is vulnerable to corrosion. Overall this diagram illustrates that attempting to cast the compound RE2TMI4B will result in a combination of free iron, RE2TMI4B and rare earth rich phases.
At present the energy product of the alloy can be maximised, thus achieving optimum magnetic properties, if the composition is cast as labelled on the diagram as Nd2Fe14B composition, which is II.76 atomic % Neodymium; 82.36 atomic % Iron: and 5.88 atomic % Boron (Nd2Fe14B). The resulting alloy contains free iron in the microstructure.
Free iron precipitation occurs in any composition up to the point labelled X' as seen in figure 2. It is known that free iron in the microstructure results in poor magnetic properties in comparison to those results that can be achieved with no free iron present.
A method of avoiding the formation of free iron in the microstructure, when casting at compositions between the Nd2Fe14B composition and the composition "X", is to add alloying additions that suppress the formation of free iron. Therefore the addition of zirconium in small concentrations, Le. up to a few atomic percent, results in depletion of the free iron volume fraction in the microstructure. It is expected that alternative group IVB metals could be used to produce a similar effect.
It is believed that the above free iron depletion occurs because when zirconium is added to rare earth-transition metal-boron-type alloys, it preferentially forms zirconium diboride (ZrB2) thus resulting in a depletion of boron throughout the alloy. If this occurs then there will be insufficient boron to form RE2TMI4B phase and an RE2TMI7 will be formed. However, RE2TMI7 is magnetically "soft" and reduces permanent magnetic properties of the alloy.
In figure 3, it can be seen that additions of up to 0.8 atomic % zirconium result in a steady decrease in the free iron volume fraction present in the microstructure. However, if we add further zirconium, we get an increase in the ratio of free iron to RE2TMI4B, which results in a lower energy product and therefore must be avoided.
Although the addition of zirconium on its own has a beneficial effect on the nature of the alloys produced, its affects are still limited. A further improvement on the nature of the alloy produced can be achieved by adding a combination of zirconium and boron to the alloy mixture.
Sufficient boron must be added to avoid depletion of boron in the microstructure, which would result in poor magnetic properties. Figure 4 shows the effect of adding zirconium together with additional boron, whereby a dramatic decrease in the free iron content of the rare earth-transition metal- boron type alloy is produced. Free iron is effectively eliminated from the microstructure when approximately 1.0 atomic % zirconium with boron is added to the alloy mixture.
In the example displayed in figure 4, this I atomic % addition of ZrB2 can be represented as an alloy composition of: Nd12.98Fe77.46B8.56Zr1.o.
Or in weight percentage terms: Nd 29.33 wt%; Fe 67.79 wt%; B 1.45 wt%; Zr 1.43 wt%.
These results show that adding zirconium at a level of between 0 and 3 wt% in conjunction with increasing boron from I to 1.7 wt% has the effect of suppressing free-iron formation in cast rare earth-iron-boron type alloys. With optimum additions in the region of 1.4 wt% Zr and 0.3 wt% B.
Claims (18)
1. A magnetic alloy comprising: 11.8 - 15.0% rare earth metal: 77.0 82.0% transitional metal; 5.3 - 9.0% boron; and up to 2.0% IVB transitional metal.
2. The alloy of claim 1, wherein the alloy comprises 12.0 - 14.5% rare earth metal.
3. The alloy of claim I or 2, wherein the alloy comprises 0.3 - 1.3% IVB transitional metal.
4. The alloy of claim 1, 2 or 3, wherein the alloy comprises 5.9 - 8.9% boron.
5. The alloy of any of claims 1-4, wherein the transitional metal is selected from the group containing: iron, cobalt, nickel, copper, zinc or a combination thereof.
6. The alloy of any of claims 1-5, wherein the group IVB transition metal is selected from the group containing: titanium, zirconium, hafnium or a combination thereof.
7. The alloy of any of claims 1-6, wherein the rare earth metal is selected from the group containing: praseodymium, neodymium, dysprosium, terbium or a combination thereof.
8. The alloy of any of claims 1-7, comprising: about 13.0% neodymium; about 77.5% iron; about 8.6% boron; and about 1.0% zirconium.
9. A permanent magnet made from the magnetic alloy of claims I to 8.
10. Method of producing a rare earth-transition metal-boron type alloy with a reduced free iron phase content, wherein the transition metal component of the alloy comprises iron, whereby at least one group IVB transition metal is added to the alloy mixture during the melting and casting of the alloy.
11. The method of claim 10, wherein zirconium is the group IVB transition metal added to the alloy mixture.
12. The method of claim 10 or 11, wherein the amount of zirconium added to the alloy mixture is not more than 3% of the total weight of the alloy mixture.
13. The method of claim 10, 11 or 12, wherein the amount of zirconium added to the alloy mixture is not more than 2% of the total weight of the alloy mixture.
14. The method of any of claims 10 - 13, wherein additional boron is also added to the alloy mixture with the group IVB transition metal.
15. The method of claim 14, wherein the amount of additional boron added to the alloy mixture is not more than I % of the total weight of the alloy mixture.
16. The method of any of claims 10 - 15, wherein the rare earth component of the alloy is provided by at least one metal selected from the group containing: praseodymium; neodymium; dysprosium; and terbium.
17. The method of any of claims 10 - 16, wherein the transition metal component of the alloy also comprises at least one further metal selected from the group containing: cobalt; nickel; copper; and zinc.
18. A rare earth-iron-boron type alloy produced by the method of claims to 17.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0423737A GB0423737D0 (en) | 2004-10-26 | 2004-10-26 | Method of reducing the free iron phase in iron containing rare earth-transition metal-boron type alloys |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0521804D0 GB0521804D0 (en) | 2005-12-07 |
| GB2419602A true GB2419602A (en) | 2006-05-03 |
Family
ID=33485216
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0423737A Ceased GB0423737D0 (en) | 2004-10-26 | 2004-10-26 | Method of reducing the free iron phase in iron containing rare earth-transition metal-boron type alloys |
| GB0521804A Withdrawn GB2419602A (en) | 2004-10-26 | 2005-10-26 | Magnetic alloy of the RE2TM14B type and a method of making magnetic alloys |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0423737A Ceased GB0423737D0 (en) | 2004-10-26 | 2004-10-26 | Method of reducing the free iron phase in iron containing rare earth-transition metal-boron type alloys |
Country Status (2)
| Country | Link |
|---|---|
| GB (2) | GB0423737D0 (en) |
| WO (1) | WO2006046050A1 (en) |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4792368A (en) * | 1982-08-21 | 1988-12-20 | Sumitomo Special Metals Co., Ltd. | Magnetic materials and permanent magnets |
| US4802931A (en) * | 1982-09-03 | 1989-02-07 | General Motors Corporation | High energy product rare earth-iron magnet alloys |
| EP0576055A1 (en) * | 1992-06-22 | 1993-12-29 | General Motors Corporation | Fine-grained anisotropic powder from melt-spun ribbons |
| US5437741A (en) * | 1990-10-09 | 1995-08-01 | Kawasaki Steel Corporation | Corrosion-resistant rare earth metal-transition metal-boron permanent magnets |
| WO2004072311A2 (en) * | 2003-02-06 | 2004-08-26 | Magnequench, Inc. | Highly quenchable fe-based rare earth materials for ferrite replacement |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5172751A (en) * | 1982-09-03 | 1992-12-22 | General Motors Corporation | High energy product rare earth-iron magnet alloys |
| US4919732A (en) * | 1988-07-25 | 1990-04-24 | Kubota Ltd. | Iron-neodymium-boron permanent magnet alloys which contain dispersed phases and have been prepared using a rapid solidification process |
| US5486240A (en) * | 1994-04-25 | 1996-01-23 | Iowa State University Research Foundation, Inc. | Carbide/nitride grain refined rare earth-iron-boron permanent magnet and method of making |
| JPH10259459A (en) * | 1997-01-14 | 1998-09-29 | Mitsubishi Materials Corp | Raw material alloy for producing rare earth magnet powder and production of rare earth magnet powder using this raw material alloy |
| DE69938811D1 (en) * | 1998-12-11 | 2008-07-10 | Shinetsu Chemical Co | Manufacturing method of a rare earth permanent magnet |
| JP4069727B2 (en) * | 2001-11-20 | 2008-04-02 | 日立金属株式会社 | Rare earth based bonded magnet compound and bonded magnet using the same |
-
2004
- 2004-10-26 GB GB0423737A patent/GB0423737D0/en not_active Ceased
-
2005
- 2005-10-26 WO PCT/GB2005/004161 patent/WO2006046050A1/en active Application Filing
- 2005-10-26 GB GB0521804A patent/GB2419602A/en not_active Withdrawn
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4792368A (en) * | 1982-08-21 | 1988-12-20 | Sumitomo Special Metals Co., Ltd. | Magnetic materials and permanent magnets |
| US4802931A (en) * | 1982-09-03 | 1989-02-07 | General Motors Corporation | High energy product rare earth-iron magnet alloys |
| US5437741A (en) * | 1990-10-09 | 1995-08-01 | Kawasaki Steel Corporation | Corrosion-resistant rare earth metal-transition metal-boron permanent magnets |
| EP0576055A1 (en) * | 1992-06-22 | 1993-12-29 | General Motors Corporation | Fine-grained anisotropic powder from melt-spun ribbons |
| WO2004072311A2 (en) * | 2003-02-06 | 2004-08-26 | Magnequench, Inc. | Highly quenchable fe-based rare earth materials for ferrite replacement |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2006046050A1 (en) | 2006-05-04 |
| GB0521804D0 (en) | 2005-12-07 |
| GB0423737D0 (en) | 2004-11-24 |
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| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |