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EP 0 255 939 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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28.07.1993 Bulletin 1993/30 |
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Date of filing: 04.08.1987 |
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Rare earth magnet and rare earth magnet alloy powder having high corrosion resistance
Seltenerdmagnet und Seltenerdlegierung-Magnetpulver mit grossem Korrosionswiderstand
Aimant à base de terre-rare et poudre pour aimants en alliage de terre-rare à haute
résistance contre la corrosion
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Designated Contracting States: |
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AT BE CH DE FR GB IT LI NL SE |
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Priority: |
04.08.1986 JP 182998/86 29.08.1986 US 901736
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Date of publication of application: |
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17.02.1988 Bulletin 1988/07 |
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Proprietor: SUMITOMO SPECIAL METALS CO., LTD. |
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Osaka (JP) |
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Inventors: |
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- Fujimura, Setsuo
Sumitomo Special Metals Co.,Ltd.
Shimamoto-cho
Mishima-gun
Osaka-fu (JP)
- Sagawa, Masato
Sumitomo Special Metals Co.,Ltd.
Shimamoto-cho
Mishima-gun
Osaka-fu (JP)
- Yamamoto, Hitoshi
Sumitomo Special Metals Co.,Ltd
Shimamoto-cho
Mishima-gun
Osaka-fu (JP)
- Hirosawa, Satoshi
Sumitomo Special Metals Co.,Ltd
Shimamoto-cho
Mishima-gun
Osaka-fu (JP)
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Representative: Diehl, Hermann O. Th., Dr. et al |
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Diehl, Glaeser, Hiltl & Partner
Patentanwälte
Postfach 19 03 65 80603 München 80603 München (DE) |
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References cited: :
EP-A- 0 134 304 EP-A- 0 237 416
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EP-A- 0 216 254
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- PATENT ABSTRACTS OF JAPAN, vol. 10, no. 209 (E-421) (2265), July 22, 1986; &JP-A-61
48 904 (HITACHI METALS LTD), 10-03-1986
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] This invention relates to an Fe-B-R type rare earth permanent magnet having high
magnetic properties. (In the present invention, R represents the rare earth elements
inclusive of Y) More particularly, it is concerned with a permanent magnet based on
rare earth element (R), boron (B) and iron (Fe), with its corrosion resistant property
being improved significantly by the particular compositional ratios of the constituent
elements.
[0002] There was previously proposed by three of the present inventors, as an improved permanent
magnet of high performance which exceeded the highest magnetic properties of the conventional
rare earth-cobalt magnet, an Fe-B-R type permanent magnet which was composed of as
the principal components iron (Fe), boron (B) and light rare earth elements such as
neodymium (Nd) and praseodymium (Pr) abundantly available in the natural resources,
but not using samarium (Sm) and cobalt (Co) which are scarcely available in the natural
resources or uncertain in the commercial availability, hence expensive (Japanese Patent
Kokai Publications No. 59-46008 and No. 59-89401 or EPA 101552).
[0003] Said inventors also succeeded in obtaining another Fe-B-R type permanent magnet having
a higher range of the Curie temperature than that of the abovementioned magnetic alloy
which ranges, in general, from 300 °C to 370 °C, by substituting cobalt (Co) for a
part of iron (Fe) (Japanese Patent Kokai Publications No. 59-64733 and No. 59-132104
or EPA 106948).
[0004] With a view to improving the temperature characteristics (in particular the coercivity
"iHc"), while retaining the Curie temperature equal to, or higher than that, and a
higher (BH)max than that, of the above-mentioned Co-containing Fe-B-R type (i.e.,
more precisely (Fe,Co)-B-R type) rare earth permanent magnet, the said inventors further
proposed still another Co-containing Fe-B-R type rare earth permanent magnet with
much more improved iHc, while still retaining a very high (BH)max of 25 MGOe* or above,
which could be realized by including at least one kind of heavy rare earth elements
such as dysprosium (Dy), terbium (Tb), etc. as a part of R of the Co-containing Fe-B-R
type rare earth permanent magnet, R mainly containing light rare earth elements such
as Nd and/or Pr (Japanese Patent Kokai Publication No. 60-34005 or EP-A-134 304).
* 1 MGOe = 7.96 k·J/m³
[0005] However, the permanent magnets having the abovementioned excellent magnetic properties
and being composed of the Fe-B-R type magnetically anisotropic sintered body contain,
as its principal constituents, those rare earth elements and iron which are apt to
be oxidized in the air and tend to gradually form stable oxides. On account of this,
when such permanent magnet is assembled in the magnetic circuit, various problems
and inconveniences would be brought about by the oxides formed on the surface of the
magnet: such as decrease in output of the magnetic circuit; irregular functioning
among the magnetic circuits; and, in other aspect, contamination of various peripheral
devices around the magnetic circuits due to scaling off of the resultant oxides from
the surface of the magnet.
[0006] In order therefore to improve the corrosion resistant property of the abovementioned
Fe-B-R type permanent magnet, there was already proposed a permanent magnet with an
anti-corrosive metal layer having been plated on its surface by the electroless plating
method or the electrolytic plating method (Japanese Patent Application No. 58-162350),
and another permanent magnet with an anti-corrosive resin layer having been coated
on its surface by the spraying method or the dipping method (Japanese Patent Application
No. 58-171907).
[0007] With this plating method, however, there still remained problem such that, since
the permanent magnet is a sintered, somewhat porous body, an acidic or alkaline solution
used for its pre-treatment before the plating procedure stays in the pores of the
sintered magnet body, which is apprehensively liable to corrode the magnet with lapse
of time; and further, since the magnet body is inferior in its chemical-resistant
property, the surface of the magnet is corroded during the plating procedure to deteriorate
its adhesion property and corrosion-resistant property.
[0008] Further, as to the latter spraying method, since the resin coating by this method
has directionality, a great deal of working steps and time are required for applying
the uniform resin coating over the entire surface of the workpiece to be treated;
in particular, coating of a magnetic body having a complicated configuration with
the coating film of a uniform thickness is all the more difficult. Furthermore, with
the dipping method, thickness of the resin coating becomes non-uniform with the consequence
that the finished product has a poor dimensional precision.
[0009] Furthermore, as the Fe-B-R type permanent magnet which could successfully solve the
disadvantages inherent in the abovementioned plating method, spraying method and dipping
method, and provide stabilized corrosion resistant property over a long period of
time, there were also proposed improved permanent magnets provided on its surface
with a vapor-deposited corrosion resistant layer composed of various metals or alloys
(Japanese Patent Applications No. 59-278489, No. 60-7949, No. 60-7950 and No. 60-7951,
now corresponding EPA 0190461). By this vapor-deposition method, oxidation of the
surface of the magnet body is suppressed, so that the magnetic property is prevented
from deterioration. Also, since there is no necessity for use of corrosive chemicals,
etc., hence there is no apprehension whatsoever of its remaining in the magnet body
as is the case with the plating method, the permanent magnet as treated by this method
is capable of retaining its stability over a long period of time.
[0010] While the vapor-deposition method is highly effective for improvement in the corrosion
resistance of the permanent magnet, it has its own disadvantage such that a special
treating apparatus is required and its productivity is low, so that the treatment
by this method is considerably expensive.
[0011] USP 4,588,439 discloses an Fe-B-R type permanent magnet alloy containing 6,000 to
35,000 ppm, (preferably 9,000 to 30,000 ppm) oxygen in order to avoid disintegration
of the sintered body based on an autoclave test. However, this alloy consumes much
rare earth elements as oxides. For complete suppression 9,000 ppm oxygen is necessary.
Namely rare earth elements of 6 times by weight of the oxygen amount is consumed to
form oxides. Such large amount of oxide is not preferred since the presence of nonmagnetic
oxides adversely affects the magnetic properties, and valuable rare earth elements
are consumed. For instance, 10,000 ppm oxygen will consume 6 % by weight of rare earth
elements as oxides.
[0012] Thus there is much to be desired in the art. Stillmore, the producing procedure and
raw materials and intermediate products must be carefully handled to avoid oxidation,
which further leads to an inrease in the production costs.
[0013] It is therefore an object of the present invention to provide an Fe-B-R type permanent
magnet material having improved corrosion resistant property.
[0014] It is another object of the present invention to provide an Fe-B-R type permanent
magnet capable of exhibiting its excellent corrosion resistant property, not by its
surface treatment for improving the corrosion resistant property thereof, but by specifying
its composition.
[0015] It is still another object of the present invention to provide an Fe-B-R type permanent
magnet having excellent durability, while maintaining its high magnetic property.
[0016] It is a further object of the present invention to provide an Fe-B-R type permanent
magnet having higher temperature characteristic.
[0017] Still further objects will become apparent in the entire disclosure.
[0018] The invention provides (Fe,Co)-B-R tetragonal type magnets as described in independent
claims 1 and 2, and (Fe,Co)-B-R tetragonal type magnet alloy powders as described
in claims 10 and 11. The invention furthermore provides processes for producing (Fe,
Co)-B-R tetragonal type magnets as described in independent claims 16, 17 and 19,
as well as processes for producing (Fe, Co)-B-R tetragonal type magnet alloy powders
as described in independent claims 20, 23 and 25. Further advantageous features are
evident from the dependent claims. The term tetragonal type is to indicate that the
major phase of the magnets or powder is of tetragonal structure.
[0019] The present invention is based on the finding, as the result of conducting various
studies and researches on the compositional aspects of the Fe-B-R type permanent magnet,
that, by specifying Nd and Dy as the rare earth element (R), and by defining specific
amounts of B, Co, Al and Fe and specific limitation of the amount of C in the magnet
(or material) composition, improvement in the corrosion resistance of the permanent
magnet (or material) could be attained without deteriorating its magnetic properties,
which improvement was so significant that it could not be realized with the conventional
permanent magnets. Further improvement may be achieved by including Ti and/or Nb in
specific amounts.
[0020] That is to say, according to the present invention, in general aspect thereof, there
is provided an (Fe,Co)-B-R tetragonal type rare earth magnet (or material) having
excellent corrosion resistant property, which consists essentially of: 0.2 - 3.0 at%
Dy and, 12 - 17 at% of the sum of Nd and Dy; 5 - 8 at% B; 0.5 - 13 at% Co; 0.5 - 4
at% Al; and the balance being Fe, the principal phase being of the tetragonal structure.
Fe should be at least 65 at%, while the sum of Fe and Co is, preferably, at least
75 at%. It is assumed that stabilization of the boundary phase is due to adding Co
and Al.
[0021] The foregoing objects, other objects and the specific composition of the (Fe,Co)-B-R
type rare earth permanent magnet (or material) according to the present invention
will become more apparent and understandable from the following detailed description
thereof, with reference to the preferred embodiments of its production and magnetic
properties, when read in conjunction with the accompanying drawing.
[0022] In the drawing:
Fig. 1 is a graphical representation of a result of the Pressure Cooker Test, showing
the length of time lapsed until the surface coating blistered or the material surface
produced oxide powders;
Fig. 2 is a graphical representation of a result of the corrosion-resistance test,
showing a relationship between the standing time and variations in weight of the samples
per unit surface area;
Figs. 3 and 4 are graphs showing the effect of Co addition where Al is 2 and 0 at%,
respectively, in weight change per unit surface area versus standing time at 80°C
x 90% R.H.;
Figs. 5 and 6 are graphs showing the effect of Al addition where Co is 4 and 0 at%,
respectively, in weight change per unit surface area versus standing time at 80°C
x 90% R.H.; and
Fig. 7 is graphs showing the effect of Co and Al at different amounts of C in magnetic
flux loss versus standing time in a testing atmosphere of 80°C x 90% R.H.
[0023] In the following, the present invention will be described in specific detail.
[0024] The rare earth permanent magnet material according to the present invention possesses
(BH)max of 25 MGOe or above and iHc of 10 kOe* or above (when made to an anisotropic
sintered magnet), and, as the result of the Pressure Cooker Test (P.C.T.) in an atmosphere
of a temperature of 125°C and a relative humidity of 85% as well as a prolonged holding
test in an atmosphere of a temperature of 80°C and a relative humidity of 90%, it
exhibits particularly superior corrosion resistant property in comparison with the
conventional Fe-B-R type rare earth permanent magnet material which has been subjected
to undercoating treatment with aluminum and then to further chromate treatment.
* 1 kOe = 79.6 k·A/m
[0025] Also, by inclusion of 0.1 - 1.0 at% of one of Ti and/or Nb in addition to the abovementioned
composition, the rare earth permanent magnet according to the present invention is
capable of improving its magnetic properties (in particular, its rectangularity in
the demagnetization curve) and its (BH)max without deteriorating the excellent corrosion
resistant property.
[0026] The grain boundary phase in this Fe-B-R type rare earth permanent magnet, in the
case where Co and Al are not contained in the alloy, is composed of: an R-rich phase
which does not substantially contain B, but a few atomic percents of Fe, and is composed
mostly of the rare earth element; and an R
1+εFe₄B₄ phase with a high content of B (about 40 at% or more). On account of this, the
deterioration in the corrosion-resistance of the Fe-B-R type rare earth permanent
magnet is considered primarily ascribable to the presence of the abovementioned R-rich
phase which contains the chemically active rare earth elements as the principal constituent.
[0027] In the case of the Fe-B-R type permanent magnet according to the present invention,
it is presumed that the Co and Al existing in the grain boundary phase enter into
the abovementioned R-rich phase to form a multi-phase which, based on the specific
control in quantity of Co and Al, and without impairing the magnetic properties, contributes
to significant improvement in the corrosion resistance of the grain boundary phase.
[0028] The magnetic properties of the Fe-B-R type magnet (or magnet material) are primarily
attributable to the Fe-B-R tetragonal type intermetallic compound expressed in terms
of the chemical formula R₂Fe₁₄B. Generally, in order to provide a magnetically anisotropic,
sintered permanent magnet of the practically high magnetic properties, the magnet
composition should be carefully selected within a region where the composition is
R-richer and B-richer than the stoichiometric composition of R₂Fe₁₄B. (Particularly
in a region where R is not sufficient, α-iron precipitates in the alloy and/or sintered
magnet which causes a ready invertion of magnetization resulting in a low coercivity.)
[0029] In the region of the R-rich and B-rich side, an R-rich phase composed almost of metallic
R and a B-rich phase expressed by R
1+EFe₄B₄ occur, which serve to improve the sintering characteristics and coercivity,
particularly, the R-rich phase smoothes the grain boundary of the tetragonal crystal
grains through the sintering (and further aging).
[0030] It has been revealed that the corrosion resistance is primarily related with this
P-rich boundary phase. The "R" in the R-rich phase is very apt to be oxidized by oxygen
and/or moisture in the ambient atmosphere. Further, if carbon (C) and/or chlorine
(Cl) are included as impurities, they are present as carbide or chloride of R, which
will readily react with moisture in the atmosphere to decompose. (Thus, generally
speaking, C and Cl should be maintained at a low level)
R becomes oxide of R (e.g., R₂O₃) which is nonmagnetic and causes the magnetic
properties to decrease as the amount of the oxide increases (particularly, Br and
(BH)max will gradually decrease). However, if there is still a certain amount of R
(i.e., more than that to be present as R-oxide) requisite for sintering to make a
magnet. That is, if the amount of R is large, oxygen may be allowed in a correspondingly
large amount. However, if the amounts of R and oxygen increases, it results in occurrence
of a large amount of the nonmagnetic phase, which leads to lowering in Br and (BH)max.
So far as the amount of R is limited (as is usual in the practice), the amount of
R will be short when a large amount of oxygen is present, which finally results in
a complete loss of coercivity.
[0031] According to the present invention, such problems ascribable to the oxidation of
the R-rich phase (or generally the boundary phase) can be eliminated by incorporation
of a certain amount of Co and Al in the composition. Particularly, the ratio of the
sum of Co and Al to the amount of rare earth elements (Rʹ) contained (or to be contained)
in the boundary phase: (Co + Al)/Rʹ is important. By controlling this ratio, the rare
earth elements contained in the boundary phase can be stabilized. A considerable amount
of Co and Al forms stable intermetallic compounds with R (e.g., NdCo₃, Nd₃Co₇, etc.;
there occur certain compounds containing Al as solid-solution) which contribute to
the corrosion resistance.
[0032] Note that a certain amount thereof forms the R₂(Fe,Co)₁₄B tetragonal type phase.
(It is presumed that some part of Al also assumes the site of Fe in this tetragonal
type crystal structure to form R₂(Fe,Co,Al)₁₄B.) These compounds have improved corrosion
resistance over the base R₂Fe₁₄B phase.
[0033] Preferably, (Co+Al)/Rʹ ranges about 0.5 to about 10 (more preferably 0.7 to 5). Below
0.5 the improvement in the corrosion resistance would not be sufficient, while above
10 the sintering characteristics will deteriorate leading to a lowering in iHc.
[0034] As a guideline for control, the amount of Rʹ can be roughly calcurated by the following
equation:
where A is the total amount of the elements contained in the tetragonal type phase
and RO is the amount (by at%) of the R-oxide (R₂O₃) in the magnet or material.
[0035] Measurement, e.g., by X-ray micro-analyser (XMA) etc. can provide definite figure
of Rʹ, Co and Al.
[0036] By the incorporation of Co and Al, the corrosion resistance not only of the final
sintered product but of the alloy material (particularly powder) therefor can be significantly
increased. For instance the alloy powder obtained by the direction reduction process
from rare earth oxide through a reduction agent, e.g., Ca can reduce the amount of
oxygen through the incorporation of Co and Al. Thus the present invention provides
significant improvement in the practical, industrial production and utilization of
the generally Fe-B-R type permanent magnets.
[0037] In the present invention, the reason for limiting the range of content for each of
the constituent elements in the rare earth permanent magnet is as follows.
[0038] With the content of Dy not reaching 0.2 at %, no increase is seen in both iHc and
(BH)max. On the contrary, with its content exceeding 3.0 at%, improvement is seen
in iHc. However, since Dy is available only in small quantity in the natural resources,
it is very expensive and hence unfavorably pushes up the production cost of the permanent
magnet. On account of this, its content is limited to a range of from 0.2 at% to 3.0
at%, or preferably from 0.2 at% to 2.0 at%. Dy also serves to improve the temperature
characteristics of the magnet particularly in reversible loss of magnetic flux at
a high temperature and irreversible loss of magnetic flux after being subjected thereat.
[0039] When the total quantity of Nd and Dy (i.e., the total quantity of the rare earth
elements) is below 12 at%, α-Fe would precipitate in the metallic compound of the
principal phase to abruptly decrease iHc. On the other hand, above 17 at%, the corrosion
resistance of the basic Fe-B-R ternary composition is deteriorated due to the occurrence
of greater amounts of R-rich phase if a large amount of Co and Al is not present (such
large amount offers problem in the magnetic properties). For these reasons, the total
quantity of Nd and Dy is limited to a range of from 12 at% to 17 at%, or preferably
from 12.5 at% to 15 at% (for achieving 30 MGOe or more and good corrosion resistance).
The amount of Nd is preferably 11 - 16 at% (more preferably 12 - 14.5 at%). At least
11 at% Nd is preferred to provide sufficient Nd-rich boundary phase, and generally
to save Dy (the latter is applied to also 16 at% Nd). However, Nd may be partly replaced
by Pr so far as the magnetic and anticorrosion properties are not affected. Similarly,
as a commertially available Nd material, Didymium containing Nd, Pr and Ce may be
partly employed.
[0040] With the content of B not reaching 5 at%, iHc unfavorably drops down to 10 kOe or
lower. On the other hand, with its content exceeding 10 at%, iHc increases, but Br
drops down to become unable to obtain (BH)max of 25 MGOe or higher. Besides, above
10 at% B, the nonmagnetic B-rich phase increases to a considerable amount. For these
reasons, the content of B is limited to a range of from 5 at% to 10 at% (preferably
6 - 8 at%).
[0041] Co is effective for increasing the Curie temperature, improving the weather-resistance
of the product and the oxidation resistance of the raw material (alloy, particularly
its powder), as well as increasing Is. With the Co content below 0.5 at%, the effect
of increasing the Curie temperature and improving the corrosion resistance of the
product (or material) is small. On the contrary, with its content exceeding 13 at%,
Co is locally concentrated to be agglomerated in the grain boundary at a high density
with the consequence that a ferromagnetic R(Nd,Dy)-Co compound containing therein
30 at% or more of Co is precipitated to readily bring about reversal of magnetization
in the Fe-B-R type rare earth permanent magnet of the present invention, resulting
in a lowered iHc. For these reasons, the content of Co is limited to a range of from
0.5 at% to 13 at%, or preferably from 1 at% to 10 at% in view of these aspects. Besides,
at 5 at% Co or more, the temperature coefficient of Br is 0.1 %/°C or less.
[0042] Al is effective for increasing iHc and, in particular, improving the corrosio resistance
of the product in cooperation with Co by synergic effect therewith. It has an effect
of improving iHc which tends to decrease with increase in the adding quantity of Co.
With the Al content below 0.5 at%, the effect of increasing iHc and improving the
corrosion resistance of the product (or material) is not satisfactory. On the contrary,
with its content exceeding 5 at%, the effect is seen in the improved iHc, but Br lowers
and (BH)max lowers below 25 MGOe. In balancing these, the content of Al is limited
to a range of from 0.5 at% to 5 at%, or preferably from 0.5 at% to 3 at%.
[0043] Ti or Nb has an effect of compensating for the decrease in Br and (BH)max due to
addition of Al. With the content of Ti or Nb not reaching 0.1 at%, no sufficient effect
of increasing Br is recognized. On the other hand, with the content thereof exceeding
1.0 at%, Ti or Nb is combined with B in the magnetic alloy to form borides of Ti or
Nb, which invites decrease (thus short) in B necessary for the magnetic alloy, entailing,
at the same time, decrease in iHc. For these reasons, the content of Ti and/or Nb
is limited to a range of from 0.1 at% to 1.0 at%, or preferably from 0.2 at% to 0.7
at%. V, Mo, W, Ta, Hf and Zr may be present each in an amount 0.1 - 1.0 at%, which
serve like Ti or Nb.
[0044] C gives also great influence on the corrosion-resistance of the permanent magnet.
C may be contained as carbide of R which will readily react with moisture in the atmosphere
to be caused to decompose. When its content exceeds 2,000 ppm, the corrosion resistance
abruptly decreases, which entails difficulty in obtaining a practical permanent magnet.
Therefore, its content should be 2,000 ppm or below, or preferably 1,000 ppm or below,
or more preferably 700 ppm or below. C tends to come from the starting materials such
as iron, ferro-boron or rare earth elements as an impurity, or sometimes through the
production process (e.g., from organic compacting aids or when solvents are used for
pulverization etc.).
[0045] In the rare earth permanent magnet or alloy material according to the present invention,
the remainder of the composition other than the abovementioned elements is Fe and
unavoidable impurities.
[0046] Fe should be present at least 65 at% since below this amount, it is difficult to
achieve 25 MGOe or more. Fe is preferably at most 81 at% since above this, α-iron
tends to precipitate. Thus Fe of 68 - 81 at% is more preferred. It should be noted
that Co may replace some part of the Fe site in the basic Fe-B-R tetragonal type crystal
structure to form the (Fe,Co)-B-R tetragonal type crystal structure.
[0047] Oxygen is generally not preferred since valuable R is consumed as oxide which is
nonmagnetic. Oxygen is believed to be present almost as R-oxide (e.g., R₂O₃) in the
magnet after sintering at 1,000°C or higher since R is chemically active. However,
oxygen is inevitably contained as the impurity because rare earth elements are generally
very apt to be oxidized by oxygen or H₂O, and it is not easy to maintain the raw materials,
production process, and intermediate and final products free from oxygen or moisture
(i.e., air). Therefore the oxygen content should be maintained as low as possible
in the sense of the practically or industrially achievable level in light of the magnetic
properties and saving (or efficiency) of R. Thus oxygen should be kept at 10,000 ppm
or below, or preferably 8,000 ppm or below (more preferably 6,000 ppm or below).
[0048] Further impurities may possibly be P, S, Mn, Ni, Si, Cu, Cr and so on, which might
be unavoidably mixed into the alloy components in the course of the industrial production.
Such impurities are allowed to be present in the magnet or material of the present
invention so far as the requisite properties are satisfied.
[0049] Chlorine (Cl) may be contained as an impurity, too, e.g., when the pulverization
of alloy is effected by wet pulverization using a solvent of organic chlorine compound
(trichlorethylene etc.). Then chlorine is contained as chloride of R which will be
readily decomposed by moisture in the air. Thus chlorine should be, if contained in
the composition, restricted to 1500 ppm or less, preferably, 1,000 ppm or less.
[0050] Nitrogen might be incorporated through the production process, e.g., jet milling
using N₂ as a pulverization medium amounting to about 1,000 ppm while wet-milling
by a ball mill using a solvent provides very low amount of nitrogen, e.g., below 100
ppm. If nitrogen is present in the magnet, it may form Nd-nitride which is very apt
to react with H₂O. Therefore it is preferred to control it to 2,000 ppm or below,
more preferably 1,000 ppm or below.
[0051] According to a preferred aspect of the present invention, there is provided a magnet
consisting essentially of: 12 to 14.5 at% of Nd; 0.2 to 2.0 at% of Dy (the total quantity
of Nd and Dy being in a range of from 12.5 to 15 at%); 6 to 8 at% of B; 1 to 10 at%
of Co; 0.5 to 3 at% of Al; 1,000 ppm or below of C; and remainder of Fe (68 - 81 at%)
and unavoidable impurities, wherein the principal phase (preferably at least 85 vol
%) is the (Fe,Co)-B-R tetragonal type crystal structure, exhibits excellent magnetic
properties of (BH)max and iHc which are 30 MGOe or higher and 13 kOe or higher, respectively,
as anisotropic sintered magnets and also exhibits very high corrosion-resistant property.
[0052] Note, however, that by applying appropriate aging, the magnet achieves still higher
magnetic properties.
[0053] Further, the permanent magnet (or material) according to the present invention exhibits
its best corrosion resistance when it contains, as the principal phase, R₂(Fe,Co)₁₄B
type compound having the tetragonal crystal structure, and has a grain boundary phase
which contains from 5 to 30 at% Co and 5 at% or less Al in the R-rich multi-phase.
The R-rich multi-phase is composed of an R-rich phase not containing therein Al but
Co and another R-rich phase containing therein both Al and Co. When the crystal grain
size of the magnet is about 1 µm - 100 µm (pref. 2 - 30 µm) the magnet provides significantly
high magnetic properties.
[0054] Methods used to produce or prepare the alloy powder include melt-casting processes
followed by crushing and/or pulverization or direct reduction processes of rare earth
oxide by means of a reduction agent.
[0055] With a view to enabling those persons skilled in the art to put the present invention
into practice, the following preferred examples are presented.
EXAMPLES
Example 1
[0056] As the starting material, use was made of electrolytic iron of 99.9 % purity (by
weight as to the purity); ferro-boron alloy (20 % B); Nd (> 97 % the balance being
Pr); Dy, Co, Al and Ti of > 99 %; ferro-niobium containing 67 % Nb. After these ingredients
were mixed at their various predetermined ratios, each mixture was molten to form
an alloy under high frequency heating, after which the molten alloy was cast in a
water-cooled copper mold. As the result, there were obtained alloy ingots of various
compositions as shown in Table 1 below. Certain amounts of Si, Mn, Cu and Cr were
incorporated originating from the ferro-boron. These elements improve iHc and rectangularity
of the demagnetization curves, which seems to be based on the presence of 300 - 5,000
ppm Si and 200 - 3,000 ppm in total of Mn, Cu and Cr in the magnet.
[0057] Thereafter, the ingot was crushed coarsely by a stamping mill, followed by wet pulverization
in a ball mill using trichloro-trifluoroethane, thereby obtaining pulverized powders
having an average particle size of 3 µm.
[0058] Each of the pulverized powders was then charged in a metal mold of a pressing device,
subjected to alignment in a magnetic field of 12 kOe, and compacted under a pressure
of 1.5 tons/cm² in the direction perpendicular to the magnetic field. The resultant
compact was then sintered at a temperature ranging from 1,040°C to 1,120°C, for two
hours in an argon atmosphere, after which it was allowed to cool. Thereafter, the
sintered body was further subjected to aging treatment at 600°C. As the result, there
were obtained the permanent magnet material specimens having a dimension of 20 mm
x 10 mm x 8 mm, which were magnetized by applying a magnetic field of at least 25
kOe.
[0059] The magnetic properties of the thus obtained permanent magnets were measured, the
results being shown in Table 1 below. The quantity of Co and Al were determined by
use of an X-ray micro-analyzer, wherein the compositional analyses of the R-rich phase
in the grain boundary were carried out. The evaluation of the analyses was given in
terms of the average values of the compositions in the grain boundary phase primarily
at the triple points.
[0060] The magnetic properties were measured after the magnetization. As is apparent from
Table 1, the Fe-B-R type permanent magnet having the composition as specified in this
invention possesses magnetic properties which are equal to, or higher than, that of
the conventional Fe-B-R type permanent magnet.
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP87111257NWB1/imgb0002)
Example 2
[0061] Some of the test specimens obtained from Example 1 above were subjected to the undercoating
treatment with Al followed by surface-treatment with chromate to provide surface-treated
specimens; and, on the other hand, the remainder were left untreated as the surface-untreated
specimens. Each group of the specimens was then subjected to the Pressure Cooker Test
(P.C.T.) in an atmosphere of a relative humidity of 85% at a temperature of 125°C
under a pressure of 2 kgf/cm². Through the P.C.T. tetragonal grains will be isolated
from the surface of the specimen through the corrosion of the boundary phase to produce
a grey colored powder. Thus the P.C.T. represents the evaluation of the corrosion
resistance primarily due to the stabilization of the boundary phase.
[0062] The test result was evaluated by the length of time taken until the surface-treated
film peeled off the surface of the specimen to bring about blisters, or the length
of time lapsed until the surface of the specimen material produced powder. Figure
1 indicates the test results.
[0063] As is apparent from Figure 1, the permanent magnets according to the present invention
which are in a state as produced and have not undergone any surface-treatment exhibit
particularly excellent corrosion resistance in comparison with that of the conventional
permanent magnets which were subjected to the surface-treatment for improving the
corrosion-resistance. The specimens which did not suffer disintegration exhibited
almost the same magnetic properties as those before testing while those of the disintegrated
specimens were not measured.
Example 3
[0064] The test specimens Nos. 2, 3, 6 and 7 in Table 1 as obtained from Example 1 above
and not subjected to the surface-treatment were subjected to the corrosion-resistance
test,in which the specimens were held in an atmosphere of a relative humidity of 90%
at temperature of 80°C over a long period of time (accelerated weather-proof test).The
test result was evaluated by increase in quantity of the oxide per unit surface area
of each specimen versus the length of time, during which the specimen was held in
the abovementioned atmosphere. The test results are shown in Figure 2. The resultant
specimens after this test produce red rust. Thus this test is an acceleration test
representing the weather proofness (or oxidation resistance) of the magnet surface
under the usual conditions of use thereof. Namely, the corrosion resistance of the
tetragonal grains as well as the boundary phase of the magnet surface is evaluated
by this test. Therefore it is necessary to apply also this test for complete evaluation
of the corrosion resistance of this type of magnets.
[0065] As is apparent from Figure 2, the permanent magnet according to the present invention
has a significantly superior corrosion resistance of such a degree that could not
be attained by the conventional Fe-B-R type rare earth permanent magnet.
Example 4
[0066] Specimens having no surface treatment were prepared based on the compositions as
shown in Table 2 and pulverization was carried out by jet-milling in N₂ gas containing
1,000 ppm oxygen, otherwise in the same manner as Example 1. In Table 2 Specimens
12 -14 did not include Co and Al. These specimens were tested by an autoclave under
a saturated steam atmosphere at 180°C for 16 hrs for the corrosion resistance. The
magnetic properties were measured before and after the corrosion resistance test,
while those before the test are shown in Table 3. The loss in weight of the specimens
versus the lapse of time was measured, too, and is shown in Table 3.
[0067] As apparent in Tables 2 and 3, specimen Nos. 9 - 11 which include Co and Al did not
suffer the loss in weight nor disintegrated, whereas specimen Nos 12 - 14 were classified
in two groups depending upon the total amount of rare earth elements, one group suffering
loss and disintegration on the surface portion and the other not.
[0068] The specimens which did not suffer disintegration demonstrated the same level of
the magnetic properties within the measurement error even after the test in the autoclave.
[0069] Acordingly it is concluded that the corrosion resistance of the Fe-B-R type magnets
can be significantly improved by incorporating specific amounts of Co and Al. Furthermore,
the corrosion resistance of the Fe-B-R type magnets is greatly affected by the total
amount of rare earth elements in the magnet or material. Generally, the amount of
the rare earth elements which are present in the boundary phase of the Fe-B-R type
magnets will increase as the total amount of R increases. Such abundant or excess
presence of R adversely affects the corrosion resistance, which, however, can be completely
eliminated by the incorporation of Co and Al. Co and Al are believed to stabilize
the boundary phase. It was further confirmed that the copresence of Co and Al has
an effect to reduce the amount of N in the sintered magnet to a half to a third of
that in the base magnet not including Co and Al.
[0070] It is also concluded that even when Co and Al are not included, the Fe-B-R type magnet
does not suffer disintegration if the total amount of R does not exceed about 14 at%
(and the level of C is low). This is believed to be attributable to the non-presence
of the abundant R-rich phase in the boundary phase.
[0071] Furthermore, the absolute amount of oxygen appears to be not definitive for the corrosion
resistance (or disintegration), not only in the case where Co and Al are included
but in the case where these are not included. Rather, the definitive factor for suppressing
the corrosion is the control of the boundary phase either by stabilizing it by Co
and Al or by eliminating the presence of excess R-rich boundary phase, i.e., more
than the minimum amount necessary to achieve the requisite high magnetic properties.
In light of this aspect, an Fe-B-R type magnet composition containing 14 at% or less
R in total in conjunction with the allowable level of impurity (particularly C etc.)
will also provide a stable base composition. (Note, however, the presence of Co and
Al further stabilize the base composition even as the material.)
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP87111257NWB1/imgb0003)
Example 5
[0072] Based on the composition as shown in Table 4 and otherwise in the same manner as
in Example 1 magnet specimens were produced and measured for the amounts of oxygen
and carbon and the magnetic properties to be shown in Table 4. The specimens were
tested in an atmosphere of a 90 % relative humidity (R.H.) at 80°C and measured for
the change in weight per unit surface of the specimen. The result is shown in Figs.
3 - 6.
[0073] Fig. 3 represents the change in weight in the case where 2 at% Al is present and
the Co amount is changed from 0 - 6 at%. When Co is not present, the corroding rate
expressed in terms of the change rate in weight is large, whereas the corroding rate
decreases to an extremely low level after the lapse of a certain period of time as
the Co amount increases.
[0074] Fig. 4 represents the change in weight in the case where Al is not present and the
Co amount is changed from 2 to 6 at%. The changing rate in weight decreases with the
lapse of time while the decreasing tendency enhances with increase in the Co amount.
In comparison to Fig. 3, Fig. 4 where Al is not present demonstrates greater change
(increase) in weight than those in Fig. 3. Such tendency is more significant in Figs.
5 and 6. Namely, Figs. 5 and 6 represent the effect of Al at a Co amount of 4 at%
and 0 % (not included). When Co is not included (Fig. 6), not remarkable effect on
the weight change test is achieved by incorporating Al, whereas when Co is included
(Fig. 5) the magnitude of the change in weight diminishes with increase in the Al
amount. Based on this fact it has turned out that the presence of Al contributes to
the improvement in the corrosion resistance.
[0075] Furthermore, based on the results of Table 4, iHc is significantly improved when
a small amount of Al (e.g., 1 at%) is contained, although iHc tends to decrease with
increase of Co when Al is not present.
[0076] As discussed hereinabove, the synergic effect of the copresence of Co and Al in the
Fe-B-R type magnets is significant in improving the corrosion resistance as well as
in providing high magnetic properties.
Example 6
[0077] Based on ingots having the compositions of Nos. 15 and 17 of Table 4, specimens containing
different amounts of C were prepared as follows; (1) jet-milling the ingot using N₂-gas
as a pulverizing medium (or carrier), (2) fine pulverization by a ball-mill using
a solvent (organic fluorine solvent, e.g., flon) as pulverizing medium, and/or (3)
to certain specimens admixing a paraffine wax to adjust the C amount.
[0078] The results including the measured magnetic properties are shown in Table 5. The
specimens were further magnetized by application of an external magnetic field of
at least 25 kOe and thereafter tested for the weather corrosion resistance in an atmosphere
of 90 % R.H. at 80°C to measure the change in the magnetic flux by using a flux meter.
The results are shown in Fig. 7.
[0079] As is apparent in Fig. 7, the flux loss generally increases with increase in C, however,
the rate of flux loss significantly diminishes at the presence of Al even when C increases,
particularly at about 500 ppm C or more.
[0080] As is apparent from the Examples, the present invention can eliminate the surface
treatment for improving the corrosion resistance. A further surface treatment may
be applied, too. However the surface treatment can be quite simplified in order to
give a complete corrosion protection, e.g., resin impregnation with epoxy or the like
resin will be sufficient.
[0081] So far, the present invention has been described with reference to particular embodiments
thereof. It should, however, be noted that changes and modifications may be made by
those persons skilled in the art within the gist of the present invention or scope
of the present invention as recited in the appended claims.
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP87111257NWB1/imgb0005)
1. An (Fe,Co)-B-R magnet where the principal phase is of tetragonal structure, which
has a stabilized R-rich grain boundary phase and a high corrosion resistance, comprising:
as R 0.2-3.0 at% Dy and 12-17 at% of the sum of Nd and Dy;
5-10 at% B;
0.5-13 at% Co;
0.5-4 at% Al; and
the balance being at least 65 at% Fe,
characterized in that
C does not exceed 1000 ppm, preferably 700 ppm, and
Cl does not exceed 1500 ppm, preferably 1000 ppm.
2. An (Fe,Co)-B-R magnet where the principal phase is of tetragonal structure which has
a stabilized R-rich grain boundary phase and a high corrosion resistance, comprising:
as R 0.2-3.0 at% Dy and 12-17 at% of the sum of Nd and Dy;
5-10 at% B;
0.5-13 at% Co;
0.5-4 at% Al; and
0.1-1.0 at% of Ti and/or Nb; and
the balance being at least 65 at% Fe,
characterized in that
C does not exceed 1000 ppm, preferably 700 ppm, and
Cl does not exceed 1500 ppm, preferably 1000 ppm.
3. The magnet as defined in one of the preceding claims, wherein the ratio, by atomic
%, of the sum of Co and Al to the amount of rare earth elements contained in the boundary
phase is 0.5-10.
4. The magnet as defined in one of the preceding claims, wherein Nd is 12-14.5 at%;
Dy is 0.2-2 at%, the total amount of Nd and Dy being 12.5-15 at%;
B is 6-8 at%;
Co is 1-10 at%;
Al is 0.5-2 at%; and
Fe is at least 68 at%.
5. The magnet as described in one of the preceding claims, wherein said R-rich boundary
phase comprises 5-30 at% Co and not exceeding 5 at% Al.
6. The magnet as defined in claim 5, wherein said R-rich boundary phase comprises a first
R-rich phase containing Co but not Al, and a second R-rich phase containing Co and
Al.
7. The magnet as defined in one of the preceding claims, wherein N does not exceed 2000
ppm, preferably 1,000 ppm.
8. The magnet as defined in one of the preceding claims, wherein oxygen does not exceed
8,000 ppm, preferably 6,000 ppm.
9. The magnet as defined in one of the preceding claims, which is an anisotropic sintered
magnet having an energy product of at least 199.0 k·Jm³ (25 MGOe), preferably 238.8
k·J/m³ (30 MGOe), and a coercivity iHc of at least 796.0 k·A/m (10 kOe), preferably
1,034.8 k·A/m (13 kOe).
10. An (Fe,Co)B-R magnet alloy powder where the principal phase is of tetragonal structure,
which has a stabilized R-rich grain boundary phase and a high corrosion resistance
comprising:
as R 0.2-3.0 at% Dy and 12-17 at% of the sum of Nd and Dy;
5-10 at% B;
0.5-13 at% Co;
0.5-4 at% Al; and
the balance being at least 65 at% Fe,
characterized in that
C does not exceed 1000 ppm and Cl does not exceed 1500 ppm.
11. An (Fe,Co)-B-R magnet alloy powder where the pricipal phase is of tetragonal structure,
which has a stabilized R-rich grain boundary phase and a high corrosion resistance,
comprising:
as R 0.2-3.0 at% Dy and 12-17 at% of the sum of Nd and Dy;
5-10 at% B;
0.5-13 at% Co;
0.5-4 at% Al; and
0.1-1.0 at% of Ti and/or Nb; and
the balance being at least 65 at% Fe,
characterized in that
C does not exceed 1000 ppm and Cl does not exceed 1500 ppm.
12. The alloy powder as defined in one of claims 10 and 11 wherein the ratio, by atomic
%, of the sum of Co and Al to the amount of rare earth elements contained in the boundary
phase is 0.5-10.
13. The alloy powder as defined in one of claims 10 to 12 wherein Nd is 12-14.5 at%;
Dy is 0.2-2 at%, the total amount of Nd and Dy being 12.5-15 at%;
B is 6-8 at%;
Co is 1-10 at%;
Al is 0.5-2 at%; and
Fe is at least 68 at%.
14. The alloy powder as defined in one of claims 10 to 13, wherein said R-rich boundary
phase comprises 5-30 at% Co and not exceeding 5 at% Al.
15. The alloy powder as defined in claim 14 wherein said R-rich boundary phase comprises
a first R-rich phase containing Co but not Al, and a second R-rich phase containing
Co and Al.
16. A process for producing an (Fe, Co)-B-R magnet where the principal phase is of tetragonal
structure, having high corrosion resistance in which R represents rare earth elements
and which has a boundary phase stabilized by Co and Al against corrosion, comprising:
providing an ingot of an alloy consisting essentially of 12-14.5 at% Nd and 0.2-3.0
at% Dy, so that the sum of Nd and Dy is 12.5-15 at%;
6-8 at% B;
0.5-8 at% Co;
0.5-3 at% Al; and
not exceeding 1000 ppm C; and
the balance being at least 68 at% Fe,
characterized in that said ingot is pulverized to a powder by wet milling using an
organic compound containing chlorine as solvent under the condition that the resultant
powder does not contain Cl in an amount exceeding 1500 ppm, and
the powder is sintered under the conditions that the resultant sintered body does
not include C in an amount exceeding 1000 ppm or Cl in an amount exceeding 1500 ppm
in the sintered body to provide a boundary phase stabilized by Co and Al against corrosion.
17. A process for producing an (Fe, Co)-B-R magnet alloy powder where the principal phase
is of tetragonal structure, having high corrosion resistance in which R represents
rare earth elements and which has a boundary phase stabilized by Co and Al against
corrosion, comprising:
providing an ingot of an alloy consisting essentially of 12-14.5 at% Nd and 0.2-3.0
at% Dy, so that the sum of Nd and Dy is 12.5-15 at%;
6-8 at% B;
0.5-8 at% Co;
0.5-3 at% Al;
not exceeding 1000 ppm C; and
the balance being at least 68 at% Fe, characterized in that
the resultant ingot is pulverized to a powder by wet milling using an organic compound
containing chlorine as solvent under the condition that the resultant powder does
not contain Cl in an amount exceeding 1500 ppm to provide a boundary phase stabilized
by Co and Al against corrosion.
18. The process as defined in claim 16 or 17, characterized in that Co is no more than
6 at%.
19. A process for producing an (Fe, Co)-B-R magnet where the principal phase is of tetragonal
structure having high corrosion resistance in which R represents rare earth elements
and which has a R-rich grain boundary phase stabilized by Co and Al against corrosion,
comprising:
providing an ingot of an alloy consisting essentially of 12-14.5 at% Nd and 0.2-3.0
at% Dy, so that the sum of Nd and Dy is 12.5-15 at%;
6-8 at% B;
0.5-8 at% Co;
0.5-3 at% Al; and
not exceeding 1000 ppm C; and
the balance being at least 68 at% Fe,
characterized in that said ingot is pulverized to a powder by jet milling in N₂ gas
under the condition that the resultant powder does not contain N in an amount exceeding
2000 ppm, and
the powder is sintered under the conditions that the resultant sintered body does
not include C in an amount exceeding 1000 ppm or N in an amount exceeding 2000 ppm
in the sintered body to provide a boundary phase stabilized by Co and Al against corrosion.
20. A process for producing an (Fe, Co)-B-R magnet alloy powder where the principal phase
is of tetragonal structure, having high corrosion resistance in which R represents
rare earth elements and which has a R-rich grain boundary phase stabilized by Co and
Al against corrosion, comprising:
providing an ingot of an alloy consisting essentially of 12-14.5 at% Nd and 0.2-3.0
at% Dy, so that the sum of Nd and Dy is 12.5-15 at%;
6-8 at% B;
0.5-8 at% Co;
0.5-3 at% Al;
not exceeding 1000 ppm C; and
the balance being at least 68 at% Fe, characterized in that the ingot is pulverized
to a powder by jet milling in N₂ gas under the condition that the resultant powder
does not contain N in an amount exceeding 2000 ppm to provide a boundary phase stabilized
by Co and Al against corrosion.
21. The process as defined in claim 19 or 20, characterized in that the pulverizing is
carried out so that N does not exceed 1000 ppm in the resultant powder.
22. The process as defined in claim 19, characterized in that the sintering is carried
out so that N does not exceed 1000 ppm in the resultant sintered body.
23. A process for producing an (Fe, Co)-B-R magnet where the principal phase is of tetragonal
structure having high corrosion resistance in which R represents rare earth elements
and which has a R-rich grain boundary phase stabilized by Co and Al against corrosion,
comprising:
providing an ingot of an alloy consisting essentially of 12-14.5 at% Nd and 0.2-3.0
at% Dy, so that the sum of Nd and Dy is 12.5-15 at%;
6-8 at% B;
0.5-8 at% Co;
0.5-3 at% Al; and
not exceeding 1000 ppm C; and
the balance being at least 68 at% Fe,
characterized in that said ingot is pulverized to a powder by wet milling in a solvent
under the condition that the resultant powder does not contain C in an amount exceeding
1000 ppm or Cl in an amount exceeding 1500 ppm, and
the powder is sintered under the conditions that the resultant sintered body does
not include C in an amount exceeding 1000 ppm nor Cl in an amount exceeding 1500 ppm
in the sintered body to provide a boundary phase stabilized by Co and Al against corrosion.
24. The process as defined in claim 16 or 23, characterized in that the sintering is conducted
under the condition that the resultant sintered body contains a rare earth rich multi-phase
as a grain boundary phase, said rare earth rich multi-phase containing 5 to 30 at%
Co and no more than 5 at% Al, and the balance being predominantly rare earth elements
Nd and Dy.
25. A process for producing an (Fe, Co)-B-R magnet alloy powder where the principal phase
is of tetragonal structure having high corrosion resistance in which R represents
rare earth elements and which has a R-rich grain boundary phase stabilized by Co and
Al against corrosion, comprising:
providing an ingot of an alloy consisting essentially of 12-14.5 at% Nd and 0.2-3.0
at% Dy, so that the sum of Nd and Dy is 12.5-15 at%;
6-8 at% B;
0.5-8 at% Co;
0.5-3 at% Al;
not exceeding 1000 ppm C; and
the balance being at least 68 at% Fe,
characterized in that the resultant ingot is pulverized to a powder by wet milling
using a solvent under the condition that the resultant powder does not contain C in
an amount exceeding 1000 ppm or Cl in an amount exceeding 1500 ppm to provide a boundary
phase stabilized by Co and Al against corrosion.
26. The process as defined in claim 16, characterized in that the pulverizing and sintering
are conducted under conditions that Cl in the sintered body does not exceed 1000 ppm.
27. The process as defined in claim 17, characterized in that the pulverizing is conducted
under conditions that Cl in the resultant powder does not exceed 1000 ppm.
28. The process as defined in claim 19, characterized in that the pulverizing and sintering
are conducted under conditions that N in the sintered body does not exceed 1000 ppm.
29. The process as defined in claim 20, characterized in that the pulverizing is conducted
under conditions that N in the resultant powder does not exceed 1000 ppm.
30. The process as defined in claim 23, characterized in that the pulverizing and sintering
are conducted under conditions that c in the sintered body does not exceed 700 ppm.
31. The process as defined in claim 25, characterized in that the pulverizing is conducted
under conditions that c in the resultant powder does not exceed 700 ppm.
32. The process as defined in claim 16 or 23, characterized in that the sintering is conducted
so that the ratio, by atomic percent, of the sum of Co and Al to the amount of rare
earth elements contained in the boundary phase is 0.5-10.
33. The process as defined in one of claims 16, 17, 19, 20, 23, or 25, characterized in
that the ingot further includes 0.1-1.0 at% of Ti, Nb or mixtures thereof.
34. The process as defined in one of claims 16, 17, 23, or 25, characterized in that the
wet milling uses a solvent containing an organic chloro-fluoro-compound--.
1. (Fe,Co)-B-R-Magnet, dessen Hauptphase eine tetragonale Struktur hat und der eine stabilisierte,
R-reiche Korngrenzenphase und eine hohe Korrosionsbeständigkeit aufweist, mit
0,2-3,0 Atom-% Dy und 12-17 Atom-% der Summe aus Nd und Dy als R; 5-10 Atom-% B; 0,5-13
Atom-% Co; 0,5-4 Atom-% Al; wobei der Rest mindestens 65 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß C 1000 ppm, vorzugsweise 700 ppm, und Cl 1500 ppm, vorzugsweise
1000 ppm, nicht übersteigen.
2. (Fe,Co)-B-R-Magnet, dessen Hauptphase eine tetragonale Struktur hat und der eine stabilisierte,
R-reiche Korngrenzenphase und eine hohe Korrosionsbeständigkeit aufweist, mit
0,2-3,0 Atom-% Dy und 12-17 Atom-% der Summe aus Nd und Dy als R; 5-10 Atom-% B; 0,5-13
Atom-% Co; 0,5-4 Atom-% Al; und 0,1-1,0 Atom-% Ti und/oder Nb; wobei der Rest mindestens
65 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß C 1000 ppm, vorzugsweise 700 ppm, und Cl 1500 ppm, vorzugsweise
1000 ppm, nicht übersteigen.
3. Magnet gemäß einem der vorhergehenden Ansprüche, bei dem das Verhältnis, ausgedrückt
in Atom-%, der Summe aus Co und Al zu der Menge an in der Grenzphase enthaltenen Seltenerdmetallen
0,5-10 beträgt.
4. Magnet gemäß einem der vorhergehenden Ansprüche, bei dem Nd 12-14,5 Atom-% und Dy
0,2-2 Atom-% beträgt, wobei die Summe aus Nd und Dy 12,5-15 Atom-% beträgt, B 6-8
Atom-%, Co 1-10 Atom-%, Al 0,5-2 Atom-% und Fe mindestens 68 Atom-% betragen.
5. Magnet gemäß einem der vorhergehenden Ansprüche, bei dem die R-reiche Grenzphase 5-30
Atom-% Co enthält und 5 Atom-% Al nicht übersteigt.
6. Magnet gemäß Anspruch 5, bei dem die R-reiche Grenzphase eine erste R-reiche Phase
aufweist, die Co, aber nicht Al enthält, und eine zweite R-reiche Phase, die Co und
Al enthält.
7. Magnet gemäß einem der vorhergehenden Ansprüche, bei dem N 2000 ppm, vorzugsweise
1000 ppm, nicht übersteigt.
8. Magnet gemäß einem der vorhergehenden Ansprüche, bei dem Sauerstoff 8000 ppm, vorzugsweise
6000 ppm, nicht übersteigt.
9. Magnet gemäß einem der vorhergehenden Ansprüche, der ein anisotroper Sintermagnet
mit einem Energieprodukt von mindestens 199,0 kJ/m³ (25 MGOe), vorzugsweise 238,8
kJ/m³ (30 MGOe), ist und eine Koerzitivkraft iHc von mindestens 796,0 kA/m (10 kOe),
vorzugsweise 1.034,8 kA/m (13 kOe) aufweist.
10. (Fe,Co)-B-R-Magnetlegierungspulver, dessen Haupt-phase eine tetragonale Struktur hat
und das eine stabilisierte, R-reiche Korngrenzenphase und eine hohe Korrosionsbeständigkeit
aufweist, mit
0,2-3,0 Atom-% Dy und 12-17 Atom-% der Summe aus Nd und Dy als R; 5-10 Atom-% B; 0,5-13
Atom-% Co; 0,5-4 Atom-% Al; wobei der Rest mindestens 65 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß C 1000 ppm und Cl 1500 ppm nicht übersteigen.
11. (Fe,Co)-B-R-Magnetlegierungspulver, dessen Haupt-phase eine tetragonale Struktur hat
und das eine stabilisierte, R-reiche Korngrenzenphase und eine hohe Korrosionsbeständigkeit
aufweist, mit
0,2-3,0 Atom-% Dy und 12-17 Atom-% der Summe aus Nd und Dy als R; 5-10 Atom-% B; 0,5-13
Atom-% Co; 0,5-4 Atom-% Al; und 0,1-1,0 Atom-% Ti und/oder Nb; wobei der Rest mindestens
65 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß C 1000 ppm und Cl 1500 ppm nicht übersteigen.
12. Legierungspulver gemäß einem der Ansprüche 10 und 11, bei dem das Verhältnis, ausgedrückt
in Atom-%, der Summe aus Co und Al zu der Menge an in der Grenzphase enthaltenen Seltenerdmetallen
0,5-10 beträgt.
13. Legierungspulver gemäß einem der Ansprüche 10 bis 12, bei dem Nd 12-14,5 Atom-% und
Dy 0,2-2 Atom-% beträgt, wobei der Gesamtbetrag von Nd und Dy 12,5-15 Atom-% beträgt,
B 6-8 Atom-%, Co 1-10 Atom-%, Al 0,5-2 Atom-% und Fe mindestens 68 Atom-% beträgt.
14. Legierungspulver gemäß einem der Ansprüche 10 bis 13, bei dem die R-reiche Grenzphase
5-30 Atom-% Co enthält und 5 Atom-% Al nicht übersteigt.
15. Legierungspulver gemäß Anspruch 14, bei dem die R-reiche Grenzphase eine erste R-reiche
Phase, die Co, aber nicht Al enthält, und eine zweite R-reiche Phase, die Co und Al
enthält, aufweist.
16. Ein Verfahren zur Herstellung eines (Fe,Co)-B-R-Magneten, dessen Hauptphase eine tetragonale
Struktur hat und der eine hohe Korrosionsbeständigkeit aufweist, bei dem R Seltenerdmetalle
darstellt und der eine durch Co und Al gegen Korrosion stabilisierte Grenzphase aufweist,
wobei das Verfahren folgendes umfaßt:
Zurverfügungstellen eines Blocks aus einer Legierung bestehend im wesentlichen aus
12-14,5 Atom-% Nd und 0,2-3,0 Atom-% Dy, so daß die Summe aus Nd und Dy als R 12,5-15
Atom-% beträgt, 6-8 Atom-% B, 0,5-8 Atom-% Co, 0,5-3 Atom-% Al, und nicht mehr als
1000 ppm C, wobei der Rest mindestens 68 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß der Block durch Naßmahlen unter Verwendung einer organischen
Verbindung, die Chlor als Lösungsmittel enthält, unter der Bedingung pulverisiert
wird, daß das erhaltene Pulver einen Cl-Gehalt von nicht mehr als 1500 ppm aufweist,
und das Pulver unter der Bedingung gesintert wird, daß der erhaltene Sinterkörper
einen C-Gehalt von nicht mehr als 1000 ppm oder einen Cl-Gehalt von nicht mehr als
1500 ppm aufweist, um eine durch Co und Al gegen Korrosion stabilisierte Grenzphase
zur Verfügung zu stellen.
17. Verfahren zur Herstellung eines (Fe,Co)-B-R-Magnetlegierungspulvers, dessen Hauptphase
eine tetragonale Struktur hat und das eine hohe Korrosionsbeständigkeit aufweist,
in dem R Seltenerdmetalle darstellt und das eine durch Co und Al gegen Korrosion stabilisierte
Grenzphase aufweist, wobei das Verfahren folgendes umfaßt:
Zurverfügungstellen eines Blocks aus einer Legierung bestehend im wesentlichen aus
12-14,5 Atom-% Nd und 0,2-3,0 Atom-% Dy, so daß die Summe aus Nd und Dy als R 12,5-15
Atom-% beträgt, 6-8 Atom-% B, 0,5-8 Atom-% Co, 0,5-3 Atom-% Al, und nicht mehr als
1000 ppm C, wobei der Rest mindestens 68 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß der erhaltene Block durch Naßmahlen unter Verwendung einer
organischen Verbindung, die Chlor als Lösungsmittel enthält, unter der Bedingung pulverisiert
wird, daß das erhaltene Pulver einen Cl-Gehalt von nicht mehr als 1500 ppm aufweist,
um eine durch Co und Al gegen Korrosion stabilisierte Grenzphase zur Verfügung zu
stellen.
18. Verfahren gemäß Anspruch 16 oder 17, dadurch gekennzeichnet, daß nicht mehr als 6
Atom-% Co vorliegen.
19. Verfahren zur Herstellung eines (Fe,Co)-B-R-Magneten, dessen Hauptphase eine tetragonale
Struktur hat und der eine hohe Korrosionsbeständigkeit aufweist, in dem R Seltenerdmetalle
darstellt und der eine durch Co und Al gegen Korrosion stabilisierte, R-reiche Korngrenzenphase
aufweist, wobei das Verfahren folgendes umfaßt:
Zurverfügungstellen eines Blocks aus einer Legierung bestehend im wesentlichen aus
12-14,5 Atom-% Nd und 0,2-3,0 Atom-% Dy, so daß die Summe aus Nd und Dy 12,5-15 Atom-%
als R beträgt, 6-8 Atom-% B, 0,5-8 Atom-% Co, 0,5-3 Atom-% Al, und nicht mehr als
1000 ppm C, wobei der Rest mindestens 68 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß der Block durch Strahlmahlen in N₂-Gas unter der Bedingung
pulverisiert wird, daß der N-Gehalt des erhaltenen Pulvers 2000 ppm nicht übersteigt,
und das Pulver unter der Bedingung gesintert wird, daß der erhaltene Sinterkörper
einen C-Gehalt von nicht mehr als 1000 ppm oder einen N-Gehalt von nicht mehr als
2000 ppm aufweist, um eine durch Co und Al gegen Korrosion stabilisierte Grenzphase
zur Verfügung zu stellen.
20. Verfahren zur Herstellung eines (Fe,Co)-B-R-Magnetlegierungspulvers, dessen Hauptphase
eine tetragonale Struktur hat und das eine hohe Korrosionsbeständigkeit aufweist,
in dem R Seltenerdmetalle darstellt und das eine durch Co und Al gegen Korrosion stabilisierte,
R-reiche Korngrenzenphase aufweist, wobei das Verfahren folgendes umfaßt:
Zurverfügungstellen eines Blocks aus einer Legierung bestehend im wesentlichen aus
12-14,5 Atom-% Nd und 0,2-3,0 Atom-% Dy, so daß die Summe aus Nd und Dy 12,5-15 Atom-%
als R beträgt, 6-8 Atom-% B, 0,5-8 Atom-% Co, 0,5-3 Atom-% Al, und nicht mehr als
1000 ppm C, wobei der Rest mindestens 68 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß der Block durch Strahlmahlen in N₂-Gas unter der Bedingung
pulverisiert wird, daß das erhaltene Pulver einen N-Gehalt von nicht mehr als 2000
ppm aufweist, um eine durch Co und Al gegen Korrosion stabilisierte Grenzphase zur
Verfügung zu stellen.
21. Das Verfahren gemäß Anspruch 19 oder 20, dadurch gekennzeichnet, daß die Pulverisierung
so durchgeführt wird, daß der N-Gehalt 1000 ppm im erhaltenen Pulver nicht übersteigt.
22. Das Verfahren gemäß Anspruch 19, dadurch gekennzeichnet, daß das Sintern so durchgeführt
wird, daß der N-Gehalt 1000 ppm im erhaltenen Sinterkörper nicht übersteigt.
23. Verfahren zur Herstellung eines (Fe,Co)-B-R-Magneten, dessen Hauptphase eine tetragonale
Struktur hat und der eine hohe Korrosionsbeständigkeit aufweist, in dem R Seltenerdmetalle
darstellt und der eine durch Co und Al gegen Korrosion stabilisierte, R-reiche Korngrenzenphase
aufweist, wobei das Verfahren folgendes umfaßt:
Zurverfügungstellen eines Blocks aus einer Legierung bestehend im wesentlichen aus
12-14,5 Atom-% Nd und 0,2-3,0 Atom-% Dy, so daß die Summe aus Nd und Dy 12,5-15 Atom-%
als R beträgt, 6-8 Atom-% B, 0,5-8 Atom-% Co, 0,5-3 Atom-% Al, und nicht mehr als
1000 ppm C, wobei der Rest mindestens 68 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß der Block durch Naßmahlen in einem Lösungsmittel unter
der Bedingung pulverisiert wird, daß das erhaltene Pulver nicht C in einer Menge,
die 1000 ppm übersteigt, oder Cl in einer Menge, die 1500 ppm übersteigt, enthält,
und das Pulver unter den Bedingungen gesintert wird, daß der erhaltene Sinterkörper
weder C in einer Menge, die 1000 ppm noch Cl in einer Menge, die 1500 ppm im Sinterkörper
übersteigt, enthält, um eine durch Co und Al gegen Korrosion stabilisierte Grenzphase
zur Verfügung zu stellen.
24. Das Verfahren gemäß Anspruch 16 oder 23, dadurch gekennzeichnet, daß das Sintern unter
der Bedingung durchgeführt wird, daß der erhaltene Sinterkörper eine seltenerdreiche
Mehrfachphase als Korngrenzenphase enthält, wobei die seltenerdreiche Mehrfachphase
5 bis 30 Atom-% Co und nicht mehr als 5 Atom-% Al enthält und der Rest hauptsächlich
aus den Seltenerdmetallen Nd und Dy besteht.
25. Verfahren zur Herstellung eines (Fe,Co)-B-R-Magnetlegierungspulvers, dessen Hauptphase
eine tetragonale Struktur hat und das eine hohe Korrosionsbeständigkeit aufweist,
in dem R Seltenerdmetalle darstellt und das eine durch Co und Al gegen Korrosion stabilisierte,
R-reiche Korngrenzenphase aufweist, wobei das Verfahren folgendes umfaßt:
Zurverfügungstellen eines Blocks aus einer Legierung bestehend im wesentlichen aus
12-14,5 Atom-% Nd und 0,2-3,0 Atom-% Dy, so daß die Summe aus Nd und Dy 12,5-15 Atom-%
beträgt, 6-8 Atom-% B, 0,5-8 Atom-% Co, 0,5-3 Atom-% Al, nicht mehr als 1000 ppm C,
wobei der Rest mindestens 68 Atom-% Fe beträgt,
dadurch gekennzeichnet, daß der erhaltene Block durch Naßmahlen unter Verwendung eines
Lösungsmittels unter der Bedingung pulverisiert wird, daß das erhaltene Pulver nicht
C in einer Menge, die 1000 ppm übersteigt oder Cl in einer Menge, die 1500 ppm übersteigt,
enthält, um eine durch Co und Al gegen Korrosion stabilisierte Grenzphase zur Verfügung
zu stellen.
26. Verfahren gemäß Anspruch 16, dadurch gekennzeichnet, daß das Pulverisieren und Sintern
unter Bedingungen durchgeführt wird, daß Cl im Sinterkörper 1000 ppm nicht übersteigt.
27. Verfahren gemäß Anspruch 17, dadurch gekennzeichnet, daß das Pulverisieren unter Bedingungen
durchgeführt wird, daß Cl im erhaltenen Pulver 1000 ppm nicht übersteigt.
28. Verfahren gemäß Anspruch 19, dadurch gekennzeichnet, daß das Pulverisieren und Sintern
unter Bedingungen durchgeführt wird, daß N im Sinterkörper 1000 ppm nicht übersteigt.
29. Verfahren gemäß Anspruch 20, dadurch gekennzeichnet, daß das Pulverisieren unter Bedingungen
durchgeführt wird, daß N im erhaltenen Pulver 1000 ppm nicht übersteigt.
30. Verfahren gemäß Anspruch 23, dadurch gekennzeichnet, daß das Pulverisieren und Sintern
unter Bedingungen durchgeführt wird, daß C im Sinterkörper 700 ppm nicht übersteigt.
31. Verfahren gemäß Anspruch 25, dadurch gekennzeichnet, daß das Pulverisieren unter Bedingungen
durchgeführt wird, daß C im erhaltenen Pulver 700 ppm nicht übersteigt.
32. Verfahren gemäß Anspruch 16 oder 23, dadurch gekennzeichnet, daß das Sintern so durchgeführt
wird, daß das Verhältnis, ausgedrückt in Atom-%, der Summe aus Co und Al zu der Menge
an in der Grenzphase enthaltenen Seltenerdmetallen 0,5-10 beträgt.
33. Verfahren gemäß einem der Ansprüche 16, 17, 19, 20, 23 oder 25, dadurch gekennzeichnet,
daß der Block außerdem 0,1-1,0 Atom-% Ti, Nb oder Gemische davon enthält.
34. Verfahren gemäß einem der Ansprüche 16, 17, 23 oder 25, dadurch gekennzeichnet, daß
beim Naßmahlen ein Lösungsmittel verwendet wird, das eine organische Chlorfluor-Verbindung
enthält.
1. Aimant du type (Fe, Co)-B-R dont la phase principale est de structure tétragonale
qui possède une phase stabilisée de joints de grains riche en R et une résistance
élevée à la corrosion, comportant :
pour R, en valeurs atomiques, 0,2 à 3,0 % de Dy et 12 à 17 % de la somme de Nd
et de Dy ;
5 à 10 % de B ;
0,5 à 13 % de Co ;
0,5 à 4 % d'Al ; et
le reste étant d'au moins 65 % de Fe,
caractérisé en ce que
C ne dépasse pas 1000 ppm, avantageusement 700 ppm, et
Cl ne dépasse pas 1500 ppm, avantageusement 1000 ppm.
2. Aimant du type (Fe, Co)-B-R où la phase principale est de structure tétragonale qui
possède une phase stabilisée de joints de grains riche en R et une résistance élevée
à la corrosion, comportant :
pour R, en valeurs atomiques, 0,2 à 3,0 % de Dy et 12 à 17 % de la somme de Nd
et Dy ;
5 à 10 % de B ;
0,5 à 13 % de Co ;
0,5 à 4 % d'Al ; et
0,1 à 1,0 % de Ti et/ou de Nb ; et
le reste étant d'au moins 65 % de Fe, caractérisé en ce que
C ne dépasse pas 1000 ppm, avantageusement 700 ppm, et
Cl ne dépasse pas 1500 ppm, avantageusement 1000 ppm.
3. Aimant selon l'une des revendications précédentes, dans lequel le rapport, en pourcentage
atomique, de la somme de Co et d'Al à la quantité d'éléments des terres rares contenus
dans la phase de joints est de 0,5 à 10.
4. Aimant selon l'une des revendications précédentes, dans lequel, en valeurs atomiques,
Nd est de 12 à 14,5 %;
Dy est de 0,2 à 2 %, la quantité totale de Nd et de Dy étant de 12,5 à 15 % ;
B est de 6 à 8 % ;
Co est de 1 à 10 % ;
Al est de 0,5 à 2 % ; et
Fe est d'au moins 68 %.
5. Aimant selon l'une des revendications précédentes, dans lequel ladite phase de joints
riche en R comprend, en valeurs atomiques, 5 à 30 % de Co et sans dépasser 5 % d'Al.
6. Aimant selon la revendication 5, dans lequel ladite phase de joints riche en R comprend
une première phase riche en R contenant Co, mais non Al, et une seconde phase riche
en R contenant Co et Al.
7. Aimant selon l'une des revendications précédentes, dans lequel N ne dépasse pas 2000
ppm, avantageusement 1000 ppm.
8. Aimant selon l'une des revendications précédentes, dans lequel l'oxygène ne dépasse
pas 8000 ppm, avantageusement 6000 ppm.
9. Aimant selon l'une des revendications précédentes, qui est un aimant fritté anisotrope
ayant un produit énergétique d'au moins 199,0 k.J/m³ (25 MGOe), avantageusement de
238,8 k.J/m³ (30 MGOe), et une coercitivité iHc d'au moins 796,0 k.A/m (10 kOe), avantageusement
de 1034,8 k.A/m (13 kOe).
10. Poudre d'alliage pour aimant de type (Fe,Co)B-R où la phase principale est de structure
tétragonale, qui possède une phase stabilisée de joints de grains riche en R et une
résistance élevée à la corrosion, comportant :
pour R, en valeurs atomiques, 0,2 à 3,0 % de Dy et 12 à 17 % de la somme de Nd
et de Dy ;
5 à 10 % de B ;
0,5 à 13 % de Co ;
0,5 à 4 % d'Al ; et
le reste étant d'au moins 65 % de Fe,
caractérisée en ce que
C ne dépasse pas 1000 ppm et Cl ne dépasse pas 1500 ppm.
11. Poudre d'alliage pour aimant de type (Fe,Co)-B-R où la phase principale est de structure
tétragonale, qui possède une phase stabilisée de joints de grains riche en R et une
résistance élevée à la corrosion, comportant :
pour R, en valeurs atomiques, 0,2 à 3,0 % de Dy et 12 à 17 % de la somme de Nd
et de Dy ;
5 à 10 % de B ;
0,5 à 13 % de Co ;
0,5 à 4 % d'Al ; et
0,1 à 1,0 % de Ti et/ou de Nb ; et
le reste étant d'au moins 65 % de Fe,
caractérisée en ce que
C ne dépasse pas 1000 ppm et Cl ne dépasse pas 1500 ppm.
12. Poudre d'alliage selon l'une des revendications 10 et 11, dans laquelle le rapport,
en pourcentage atomique, de la somme de Co et d'Al à la quantité d'éléments des terres
rares contenus dans la phase de joints est compris entre 0,5 et 10.
13. Poudre d'alliage selon l'une des revendications 10 à 12, dans laquelle, en valeurs
atomiques, Nd est de 12 à 14,5 % ;
Dy est de 0,2 à 2 %, la quantité totale de Nd et de Dy étant de 12,5 à 15 % ;
B est de 6 à 8 % ;
Co est de 1 à 10 % ;
Al est de 0,5 à 2 % ; et
Fe est d'au moins 68 %.
14. Poudre d'alliage selon l'une des revendications 10 à 13, dans laquelle ladite phase
de joints riche en R comprend 5 à 30 % de Co, et sans dépasser 5 % d'Al, en valeurs
atomiques.
15. Poudre d'alliage selon la revendication 14, dans laquelle ladite phase de joints riche
en R comprend une première phase riche en R contenant Co, mais non Al, et une seconde
phase riche en R contenant Co et Al.
16. Procédé pour produire un aimant du type (Fe, Co)-B-R où la phase principale est de
structure tétragonale, ayant une résistance élevée à la corrosion, où R représente
des éléments des terres rares, et qui possède une phase de joints stabilisée par Co
et Al contre la corrosion, consistant :
à produire un lingot d'un alliage constitué essentiellement, en valeurs atomiques,
de 12 à 14,5 % de Nd et de 0,2 à 3,0 % de Dy, de manière que la somme de Nd et de
Dy, en tant que R, soit de 12,5 à 15 % ;
de 6 à 8 % de B ;
de 0,5 à 8 % de Co ;
de 0,5 à 3 % d'Al ; et
sans dépasser 1000 ppm de C ; et
le reste étant d'au moins 68 % de Fe,
caractérisé en ce que ledit lingot est pulvérisé en une poudre par un broyage au
mouillé en utilisant un composé organique contenant du chlore en tant que solvant
sous la condition que la poudre résultante ne contienne pas de Cl en quantité dépassant
1500 ppm, et
la poudre est frittée sous les conditions que le corps fritté résultant ne comprenne
pas de C en quantité dépassant 1000 ppm ou de Cl en quantité dépassant 1500 ppm dans
le corps fritté pour produire une phase de joints stabilisée par Co et Al contre la
corrosion.
17. Procédé pour produire une poudre d'alliage pour aimant de type (Fe, Co)-B-R où la
phase principale est de structure tétragonale ayant une résistance élevée à la corrosion,
où R représente des éléments des terres rares et qui possède une phase de joints stabilisée
par Co et Al contre la corrosion, consistant :
à produire un lingot d'un alliage constitué essentiellement, en valeurs atomiques,
de 12 à 14,5 % de Nd et de 0,2 à 3,0 % de Dy, de manière que la somme de Nd et de
Dy, en tant que R, soit de 12,5 à 15 % ;
de 6 à 8 % de B ;
de 0,5 à 8 % de Co ;
de 0,5 à 3 % d'Al ;
sans dépasser 1000 ppm de C ; et
le reste étant d'au moins 68 % de Fe, caractérisé en ce que
ledit lingot résultant est pulvérisé en une poudre par broyage au mouillé en utilisant
un composé organique contenant du chlore en tant que solvant sous la condition que
la poudre résultante ne contienne pas de Cl en quantité dépassant 1500 ppm pour produire
une phase de joints stabilisée par Co et Al contre la corrosion.
18. Procédé selon la revendication 16 ou 17, caractérisé en ce que Co ne dépasse pas 6
% en valeurs atomiques.
19. Procédé pour produire un aimant de type (Fe, Co)-B-R où la phase principale est de
structure tétragonale, ayant une résistance élevée à la corrosion, où R représente
des éléments des terres rares, et qui possède une phase de joints de grains riche
en R, stabilisée par Co et Al contre la corrosion, consistant :
à produire un lingot d'un alliage constitué essentiellement, en valeurs atomiques,
de 12 à 14,5 % de Nd et de 0,2 à 3,0 % de Dy, de manière que la somme de Nd et de
Dy soit de 12,5 à 15 %, en tant que R ;
de 6 à 8 % de B ;
de 0,5 à 8 % de Co ;
de 0,5 à 3 % d'Al ; et
sans dépasser 1000 ppm de C ; et
le reste étant d'au moins 68 % de Fe,
caractérisé en ce que ledit lingot est pulvérisé en une poudre par broyage par
jets dans du N₂ gazeux sous la condition que la poudre résultante ne contienne pas
de N en quantité dépassant 2000 ppm, et
la poudre est frittée sous les conditions que le corps fritté résultant ne comprenne
pas de C en quantité dépassant 1000 ppm ou de N en quantité dépassant 2000 ppm dans
le corps fritté pour produire une phase de joints stabilisée par Co et Al contre la
corrosion.
20. Procédé pour produire une poudre d'alliage pour aimant de type (Fe, Co)-B-R où la
phase principale est de structure tétragonale, ayant une résistance élevée à la corrosion,
où R représente des éléments des terres rares, et qui possède une phase de joints
de grains riche en R, stabilisée par Co et Al contre la corrosion, consistant :
à produire un lingot d'un alliage constitué essentiellement, en valeurs atomiques,
de 12 à 14,5 % de Nd et de 0,2 à 3,0 % de Dy, de manière que la somme de Nd et de
Dy, soit de 12,5 à 15 %, en tant que R ;
de 6 à 8 % de B ;
de 0,5 à 8 % de Co ;
de 0,5 à 3 % d'Al ;
sans dépasser 1000 ppm de C ; et
le reste étant d'au moins 68 % de Fe,
caractérisé en ce que le lingot est pulvérisé en une poudre par broyage par jets
dans du N₂ gazeux sous la condition que la poudre résultante ne contienne pas de N
en quantité dépassant 2000 ppm pour produire une phase de joints stabilisée par Co
et Al contre la corrosion.
21. Procédé selon la revendication 19 ou 20, caractérisé en ce que la pulvérisation est
effectuée de façon que N ne dépasse pas 1000 ppm dans la poudre résultante.
22. Procédé selon la revendication 19, caractérisé en ce que le frittage est effectué
de façon que N ne dépasse pas 1000 ppm dans le corps fritté résultant.
23. Procédé pour produire un aimant de type (Fe, Co)-B-R où la phase principale est de
structure tétragonale, ayant une résistance élevée à la corrosion, où R représente
des éléments des terres rares et qui possède une phase de joints de grains riche en
R, stabilisée par Co et Al contre la corrosion, consistant :
à produire un lingot d'un alliage constitué essentiellement, en valeurs atomiques,
de 12 à 14,5 % de Nd et de 0,2 à 3,0 % de Dy, de manière que la somme de Nd et de
Dy soit de 12,5 à 15 %, en tant que R ;
de 6 à 8 % de B ;
de 0,5 à 8 % de Co ;
de 0,5 à 3 % d'Al ; et
sans dépasser 1000 ppm de C ; et
le reste étant d'au moins 68 % de Fe,
caractérisé en ce que ledit lingot est pulvérisé en une poudre par broyage au mouillé
dans un solvant sous la condition que la poudre résultante ne contienne pas de C en
quantité dépassant 1000 ppm ou de Cl en quantité dépassant 1500 ppm, et
la poudre est frittée sous les conditions que le corps fritté résultant ne comprenne
pas de C en quantité dépassant 1000 ppm ni de Cl en quantité dépassant 1500 ppm dans
le corps fritté pour produire une phase de joints stabilisée par Co et Al contre la
corrosion.
24. Procédé selon la revendication 16 ou 23, caractérisé en cde que le frittage est conduit
sous la condition que le corps fritté résultant contienne une phase multiple riche
en terres rares en tant que phase de joints de grains, ladite phase multiple riche
en terres rares contenant, en valeurs atomiques, 5 à 30 % de Co et pas plus de 5 %
d'Al, et le reste étant principalement des éléments Nd et Dy des terres rares.
25. Procédé pour produire une poudre d'alliage pour aimant de type (Fe, Co)-B-R où la
phase principale possède une structure tétragonale, ayant une résistance élevée à
la corrosion, où R représente des éléments des terres rares et qui possède une phase
de joints de grains riche en R, stabilisée par Co et Al contre la corrosion, consistant
:
à produire un lingot d'un alliage constitué essentiellement, en valeurs atomiques,
de 12 à 14,5 % de Nd et de 0,2 à 3,0 % de Dy, de manière que la somme de Nd et de
Dy soit de 12,5 à 15 % ;
de 6 à 8 % de B ;
de 0,5 à 8 % de Co ;
de 0,5 à 3 % d'Al ;
sans dépasser 1000 ppm de C ; et
le reste étant d'au moins 68 % de Fe,
caractérisé en ce que le lingot résultant est pulvérisé en une poudre par broyage
au mouillé en utilisant un solvant sous la condition que la poudre résultante ne contienne
pas de C en quantité dépassant 1000 ppm ou de Cl en quantité dépassant 1500 ppm pour
produire une phase de joints stabilisée par Co et Al contre la corrosion.
26. Procédé selon la revendication 16, caractérisé en ce que la pulvérisation et le frittage
sont conduits sous les conditions que Cl dans le corps fritté ne dépasse pas 1000
ppm.
27. Procédé selon la revendication 17, caractérisé en ce que la pulvérisation est conduite
sous les conditions que Cl dans la poudre résultante ne dépasse pas 1000 ppm.
28. Procédé selon la revendication 19, caractérisé en ce que la pulvérisation et le frittage
sont conduits sous les conditions que N dans le corps fritté ne dépasse pas 1000 ppm.
29. Procédé selon la revendication 20, caractérisé en ce que la pulvérisation est conduite
sous les conditions que N dans la poudre résultante ne dépasse pas 1000 ppm.
30. Procédé selon la revendication 23, caractérisé en ce que la pulvérisation et le frittage
sont conduits sous les conditions que C dans le corps fritté ne dépasse pas 700 ppm.
31. Procédé selon la revendication 25, caractérisé en ce que la pulvérisation est conduite
sous les conditions que C dans la poudre résultante ne dépasse pas 700 ppm.
32. Procédé selon la revendication 16 ou 23, caractérisé en ce que le frittage est conduit
de manière que le rapport, en pourcentage atomique, de la somme de Co et de Al à la
somme des éléments des terres rares contenus dans la phase de joints soit compris
entre 0,5 et 10.
33. Procédé selon l'une des revendications 16, 17, 19, 20, 23 ou 25, caractérisé en ce
que le lingot comprend en outre 0,1 à 1,0 %, en valeurs atomiques, de Ti, de Nb ou
de mélanges de ceux-ci.
34. Procédé selon l'une des revendications 16, 17, 23 ou 25, caractérisé en ce que le
broyage au mouillé utilise un solvant contenant un composé organique chloré et fluoré.