Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1315571
SPECIFICATION
TITLE OF THE INVE~3TION
MAGNETIC MATERIALS AND PERMANENT MAGNETS
FIELD OF THE INVENTION
The present invention relates to improvements in the
: temperature dependency of the magnetic properties of magnetic
materials and permanent magnets based on Fe-B-R systems. In
the present disclosure, R denotes rare earth element inclusive
of yttrium.
BAC~GROUND OF THE INVENTION
Magnetic materials and permanent magnet materials are
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one of the important electric and electronic materials applied
in an extensive range from various electrical appliances for
domestic use to peripheral terminal devices of large-scaled
computers. In view of recent needs for miniaturization and
S high efficiency of electric and electronic equipments, there
has been an increasing demand for upgrading of permanent
magnet materials and generally magnetic materials.
The permanent magnet materials developèd yet include
alnico, hard ferrite and samarium-cobalt (SmCo) base materials
which are well-known and used in the art. Among these,
alnico has a high residual magnetic flux density (hereinafter
referred to Br) but a low coercive force (hereinafter referred
to Hc), whereas hard ferrite has high Hc but low Br.
Advance in electronics has caused high integration and
miniaturization of electric components. However, the magnetic
circuits incorporated therein with alnico or hard ferrite
increase inevitably in weight and volume, compared with other
components. On the contrary, the SmCo base magnets meet a
demand for miniaturization and high efficiency of electric
2~ circuits due to their high Br and Hc. However, samarium is
rare natural resource, while cobalt should be included 50 - 60
wt ~ therein, and is also distributed at limited areas so that
its supply is unstable.
Thus, it is desired to develop novel permanent magnet
materials free from these drawbacks.
If it could be possible to use, as the main component
for the rare earth elements use be made of light rare earth
,
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elements that occur abundantly in ores without employing much
cobalt, the rare earth magnets could be used abundantly and
with less expense in a wider range. In an effort made to
obtain such permanent magnet materials, R-Fe2 base
S compounds, wherein R is at least one of rare earth metals,
have been investigated. A. E. Clark has discovered that
sputtered amorphous TbFe2 has an energy product of 29.5 MGOe
at 4.2 K, and shows a coercive force Hc = 3.4 kOe and a
maximum energy product (BH)max = 7 MGOe at room temperature
upon heat-treated at 300 - 500 C. Reportedly, similar
investigations on SmFe2 indicated that 9.2 MGOe was reached
at 77 K. However, these materials are all obtained by
sputtering in the form of thin films that cannot be generally
used as magnets, e.g., speakers or motors. It has further
been reported that melt-quenched ribbons of PrFe base alloys
show a coercive force Hc of as high as 2.8 kOe.
In addition, Koon et al discovered that, with
melt-quenched amorphous ribbons of
(FeO 82B0~18)0~9Tbo~05La0~05~ Hc Of 9 kOe was
reached upon annealed at 627 C ~Br=5kG). However, (BH)max is
then low due to the unsatisfactory loop squareness of
magnetization curves (N. C. Koon et al, Appl. Phys. Lett. 39
(10), 1981, pp. 840 - 842).
Moreover, L. Kabacoff et al reported that among
melt-quenched ribbons of (FeO 8Bo.2)1-xPrx (x=0-0.03
atomic ratio)~ certain ones of the Fe-Pr binary system show Hc
on the kilo oersted order at room temperature.
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These melt-quenched ribbons or sputtered thin films are
not any practical permanent magnets (bodies) that can be used
as such. It would be practically impossible to obtain
practical permanent magnets from these ribbons or thin films.
That is to say, no bul~ permanent magnet bodies of any
desired shape and size are obtainable from the con~entional
Fe-B-R base melt~quenched ribbons or R-Fe base sputtered thin
films. Due to the unsatisfac~ory loop squareness (or
rectangularity) of the demagnetization curves, the Fe-B-R base
ribbons heretofore reported are not taken as the practical
permanent magnet materials comparable with the conventional,
ordinary magnets. Since both the sputtered thin films and the
melt-quenched ribbons are magnetically isotropic by nature, it
is indeed almost impossible to obtain therefrom magnetically
anisotropic (hereinbelow referred to "anisotropic") permanent
magnets for the practical purpose comparable to the
conventional hard ferrite or SmCo magnets.
SUMM~RY OF THE DISCLOSURE
An essential object of the present invention is to
provide novel magnetic materials and permanent magnets based
on the fundamen~al composition of Fe-B-R having an improved
temperature dependency of tha magnetic properties.
Another object of the present invention is to provide
novel practical permanent magnets and magnetic materials which
do not share any disadvantages of the prior art magnetic
materials hereinabove mentioned.
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A further object of the present invention is to
provide novel magnetic materials and permanent magnets having
good temperature dependency and magnetic properties at room or
elevated temperatures.
5A still further object of the presen~ invention is to
provide novel magnetic materials and permanent magnets which
can be formed into any desired shape and practical size.
A still further object of the present invention is to
provide novel permanent magnets having magnetic anisotropy and
10excelling in both magnetic properties and mechanical strength.
A still further object of the present invention is to
provide novel magnetic materials and permanent magnets in
which as R use can effectively be made of rare earth element
occurring abundantl~ in nature.
15Other objects of ~he present invention will become
apparent from the entire disclosure given herein.
The magnetic materials and permanent magnets ac~ording
to the present invention are essentially formed of alloys
comprising novel intermetallic compounds, and are crystalline,
20sa1d intermetallic compounds being characterized at least by
new Curie points Tc.
In the followings the term "percent" or "%" denotes the
atomic percent (abridged as "at %") if not otherwise
specified.
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According to the first aspect of the present
invention, there is provided a magnetic material comprising
Fe, B, R (at least one of rare earth element including Y),
Co and M, wherein M is selected from the group given below
in an amount of from zero (0) at % to an amount of no more
than the values specified below, wherein when more than
one element comprises M, the sum of M is no more than the
maximum value among the values specified below of said
elements M actually added, M being:
4.5% Ti, 8.0% Ni, 5.0% Bi,
9.5% V, 12.5% Nb, 10.5% Ta,
8.5% Cr, 9.5% Mo, 9.5% W,
8.0% Mn, 9.5% Al, 2.5% Sb,
7.0% Ge, 3.5% Sn, 5.5% Zr,
and 5.5% Hf;
and having its major phase formed of Fe-Co-B-R type
compound that is of the substantially tetragonal system
crystal structure.
According to the second aspect of the present
invention, there is provided a sintered magnetic material
having its major phase formed of a compound consisting
essentially of, in atomic ratio, 8 to 30% of R (wherein R
represents at least one of rare earth element including Y),
2 to 28% of B, no more than 50% of Co (except that the
amount of Co is zero), M(as defined above) and the balance
being Fe and impurities.
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According to the third aspect of the present invention,
there is provided a sintered magnetic material having a
composition similar to that of the aforesaid sintered magnetic
material, wherein the major phase is formed of an Fe-Co-B-R
type compound that is of the substantially tetragonal system.
According to the fourth aspect of the present
invention, there is provided a sintered permanent magnet (an
Fe-Co-B-R base permanent magnet) consisting essentially of,
in atomic ratio, 8 to 30 % of R (at least one of rare earth
element including Y), 2 to 28 % of B, no more than 50 ~ of Co
(except that the amount of Co is zero), ~ (as defined above)
and the balance being Fe and impurities. This magnet is anisotropic.
According to the fifth aspect of the prese~t invention,
there i8 provided a sintered anisotropic permanent magne~
ha~ing a composition similar to that of the fourth permanent
magnet, wherein the major phase is formed by an Fe-Co-B-R type
compound that is of the substantially tetragonal system
crystal structure.
,;,,~ ,,,~,
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Fe-Co-B-R base magnetic materials according to the 6th
to 8th aspects of the present invention are obtained by adding
to the first - third magnetic materials the following
additional elements M, provided, however, that the additional
elements M shall individually be added in amounts less than
the values as specified below, and that, when two or more
elements M are added, the total amount thereof shall be less
than the upper limit of the element that is the largest, among
the elements actually added (For instance, Ti, V and Nb are
added, the sum of these must be no more than 12.5 % in all.):
4.5 % Ti,8.0 % Ni,5.0 % Bi,
9.5 % V,12.5 % Nb,10.5 ~ Ta,
8.5 % Cr,9.5 % Mo,9.5 % W,
8.0 ~ Mn,9.5 % Al,2.5 % Sb,
7.0 % Ge,3.5 % Sn,5.5 % Zr,
and 5.5 ~ Hf.
F~-B-R-Co base permanent magnets according to the 9th
to and 10th aspects of the present invention are obtained by
adding respectively to the 4th and 5th permanent magnets the
aforesaid additional elements M on the same condition.
Due to the inclusion of Co, the invented magnetic
materials and permanent magnets ha~e a Curie point higher than
that of the Fe-B-R type system or the Fe-B-R-M type system.
With the permanent magnets of the present invention,
practically useful magnetic properties are obtained if the
mean crystal grain size of the intermetallic compound is in a
range of about 1 to about 100 ~m for both the Fe-Co-B-R and
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Fe-Co-B-R-M systems.
Furthermore, the inventive permanent magnets can
exhibit good magnetic properties by containing l vol. % or
highèr of nonmagnetic intermetallic compound phases.
The inventive magnetic materials are advantageous in
that they can be obtained in the form of at least as-cast
alloys, or powdery or granular alloys or sintered bodies in
any desired shapes, and applied to magnetic recording media
(such as magnetic recording tapes) as well as magnetic paints,
magnetostrictive materials, thermosensitive materials and the
like. Besides, the magnetic materials are useful as the
intermediaries for the production of permanent magnets.
The magnetic materials and permanent magnets according
to the present invention are superior in mechanical strength
and machinability to the prior art alnico, R-Co type magnets,
ferrite, etc., and has high resistance against chipping-off on
machining.
In the following the present invention will be
elucidated with reference to the accompanying Drawings which,
however, are being presented for illustrative purpose.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing relationship between the
Curie point and the amount of Co of one embodiment of the
present invention, with the atomic percent of Co as abscissa;
Fig. 2 is a graph showing the relationship between the
amount of B and Br as well as iHc (kOe) of one embodiment of
;
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Fe-lOCo-xB-15Nd, with the atomic percent of B as abscissa;
Fig. 3 is a graph showing the relationship between the
amount of Nd and Br ~kG) as well as iHc ~kOe) of one
embodiment of Fe-lOCo-8B-xNd, with the atomic percent of Nd as
abscissa;
Fig. 4 is a view showing the demagnetization curves of
one embodiment of the present invention ~1 is the initial
magnetization curve 2 the demagnetization curve), with 4~I
~kG) as ordinate and a magnetic field H ~kOe) as abscissa;
Fig. 5 is a graph showing the relationship between the
amount of Co ~abscissa) and the Curie point o~ one embodiment
of the present invention;
Fig. 6 is a graph showing the demagnetization curves of
one embodiment of the present invention, with a magnetic field
H lkOe) as abscissa and 4~I (kG) as ordinate;
Figs. 7 to 9 are graphs showing the relationship
between the amount of additional elements M and the residual
magnetization Br (kG);
Fig. 10 is a graph showing the relationship between iHc
and the mean crystal grain size D (log-scale abscissa in ~m)
of one embodiment of the present invention;
Fig. 11 is a graph showing the demagnetization curves
of one embodiment of the present invention;
Fig. 12 is a Fe-B-R ternary system diagram showing
compositional ranges corresponding to the maximum energy
products (BH~max (MGOe) for one embodiment of an Fe-5Co-B-R
system;
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-- 10 --
Fig. 13 is a graph showing the relationship between
the amount of Cu, C, P and S (abscissa) and Br of one
embodiment o~ the present invention;
Fig. 14 is an X-ray diffraction pattern of one
embodiment of the invention; and
Fig. 15 is a flow chart of the experimental procedures
of powder X-ray analysis and demagnetization curve
measurements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present inventors have found magnetic materials
and permanent magnets of the Fe-B-R system the magnets
comprised of magnetically anisotropic sintered bodies to
be new high-performance permanent magnets without
employing expensive Sm and Co, and disclosed them in a
Canadian patent application filed on July 4, 1933 No.
431,730. The Fe-B-R base permanent magnets contain Fe as
the main component and light-rare earth elements as R,
primarily Nd and Pr, which occur abundantly in nature, and
contain no Co. Nonetheless, they are excellent in that
2Q they can show an energy product reaching as high as
25 - 35 MGOe or higher. The Fe-B-R base permanent magnets
possess high characteristics at costs lower than required
in the case with the conventional alnico and rare earth-
cobalt alloys. That is to say, they offer higher cost-
performance and, hence, greater advantages as they stand.
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As disclosed in the above Application, the Fe-B-R base
permanent magnets have a Curie point of generally about
3()0C and at most 370C. Such a Curie point is consider-
ably low, compared with the Curie points amounting to about
800C of the prior art alnico or R-Co base permanent
magnets. Thus, the Fe-B-R base permanent magnets have
their magnetic properties more dependent upon temperature,
as compared with the alnico or R-Co base magnets, and are
prone to deteriorate magnetically when used at elevated
temperatures.
As mentioned above, the present invention has for its
principal object to improve the temperature dependency of
the magnetic properties o~ the Fe-B R base magnets and
generally magnetic materials. According to the present
invention, this object is achieved by substituting part of
Fe, a main component of the Fe-B-R base magnets, with Co
so as to increase the Curie point of the resulting alloy.
The results of researches have revealed that the Fe-B-R
base magnets are suitably used in a usual range of not
higher than 70C~ since the magnetic properties deteriorate
at temperature higher than about 100C. As a result of
various experiments and studies, it has thus been found
that the substitution of Co for Fe is effective for
improving the resistance to the temperature dependency of
the Fe-B-R base permanent magnets and magnetic materials.
More specifically, the present invention provides
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permanent magnets comprised of anisotropic sintered bodies
consisting essentially of, in atomic percent, 8 to 30 % R
(representing at least one of rare earth element including
yttrium), 2 to 28 % of B and the balance being Fe and
inevitable impurities, in which part of Fe is substituted with
Co to incorporate 50 at ~ or less of Co in the alloy
compositions, whereby the temperature dependency of said
permanent magnets are substantially increased to an extent
comparable to those of the prior art alnico and R-Co base
alloys.
According to the present invention, the presence of Co
does not only improve the temperature dependency of the Fe-B-R
base permanent magnets, but also offer additional advantages.
That is to say, it is possible to attain high magnetic
properties through the use of light-rare earth elements such
as Nd and Pr which occur abundantly in nature. Thus, the
present,Co-substituted Fe-B-R base magnets are superior to the
existing R-Co base magnets from the standpoints of both
natural resource and cost as well as magnetic properties.
It has further been revealed from extensive experiments
that the resistance to the temperature dependency and the
magnetic properties best-suited for permanent magnets are
attained in the case where part of Fe is replaced by Co, the
crystal structure is substantially of the tetragonal system,
and the mean crystal grain size of the sintered body having a
substan~ially tetragonal system crystal structure is in a
certain range. Thus, the present invention makes it possible
- 13 ~ 1 3 1 5 57 1
to ensure industrial production of high-performance sintered
permanent magnets based on the Fe-Co-B-R system in a stable
malnner .
By measurements, it has been found that the Fe-Co-B-R
base alloys bave a high crystal magnetic anisotropy constant
Ku and an anisotropic magnetic field Ha standing comparison
with that of the existing Sm-Co base magnets.
According to the theory of the single domain particles~
magnetic substances having high anisotropy field Ha
potentially provide fine particle type magnets with
high-performance as is the case with the hard ferrite or SmCo
base magnets. From such a viewpoint, sintered, fine particle
type magnets were prepared with wide ranges of composition and
varied crystal grain size after sintering to determine the
permanent magnet properties thereof.
As a consequence, it has been found that the obtained
magnet properties correlate closely with the mean crystal
grain size after sintering. In general, the single magnetic
domain, fine particle type magnets magnetic walls which are
formed within each particles, if the particles are large. For
this reason, inversion of magnetization easily takes place due
to shifting of the magnetic walls, resulting in a low Hc. On
the contrary, if the particles are reduced in size to below a
certain value, no magnetic walls are formed within the
particles. For this reason, the inversion of magnetization
proceeds only by rotation, resulting in high Hc. The critical
size defining the single magnetic domain varies depending upon
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diverse materials, and has been thought to be about 0.01 ~m
for iron, about 1 ~m for hard ferrite, and about 4 ~m for
SmCo .
The Hc of various materials increases around their
critical size. In the Fe-Co-B-R base permanent magnets of the
present invention, Hc of 1 kOe or higher is obtained when the
mean crystal grain size ranges from 1 to 100 ~m, while Hc of 4
kOe or higher is obtained in a range of 1.5 to 50 ~m.
The permanent magnets according to the present
invention are obtained as sintered bodies. Thus, the crystal
grain size of the sintered body after sintering is of the
primary concern. It has experimentally been ascertained that,
in order to allow the Hc of the sintered compact to exceed 1
kOe, the mean crystal grain size should be no less than about
1 ym after sintering. In order to obtain sintered bodies
having a smaller crystal grain size than this, still finer
powders should be prepared prior to sintering. However, it is
then believed that the Hc of the sintered bodies decrease
considerably, since the fine powders of the Fe-Co-B-R alloys
are susceptible to oxidation, the influence of distortion
applied upon the fine particles increases, superparamagnetic
substances rather than ferromagnetic substances are obtained
when ~he grain size is excessively reduced, or the like. When
the crystal grain size exceeds 100 ~m, the obtained particles
are not single magnetic domain particles, and include magnetic
walls therein, so that the inversion of magnetization easily
takes place, thus leading to a drop in Hc~ A grain size of no
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more than 100 ~ m is required to obtain Hc of no less than 1
kOe. Particular preference is given to a range of 1.5 to 50
~rn, within which Hc of 4 kOe or higher is attained.
It should be noted that the Fe-Co-B-R-M base alloys to
be discussed later also exhibit the magnetic properties useful
for permanent magnets, when the mean crystal grain size is
between about 1 and about 100 ~m, preferably 1.5 and 50 ~m.
It is generally observed that, as the amount of Co
incorporated in Fe-alioys increases, some Fe alloys increase
in Curie `point (Tc), while another decrease in that point.
For this reason, the substitution of Fe with Co generally
causes complicated results which are almost unexpectable. As
an example, reference is made to the substitution of Fe in
RFe3 compounds with Co. As the amount of Co increases, Tc
lS first increases and peakes substantially at a point where a
half of Fe is replaced by Co, say, R(FeO 5Co0 5~3 is
obtained, and thereafter decreases. In the case of Fe2B
alloys, Tc decreases with certain gradient by the substitution
of Fe with Co.
According to the present invention, it has been noted
that, as illustrated in Fig. 1, Tc increases with increases in
the amount of Co, when Fe of the Fe-B-R system is substituted
with Co. Parallel tendencies have been observed in all the
Fe-B-R type alloys regardless of the type of R. Even a slight
amount of Co is effective for the increase in Tc and, as will
be seen from a (77-x)Fe-xCo-8B-15Nd alloy shown by way of
example in Fig. 1, it is possible to obtain alloys having any
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desired Tc between about 310 and about 750C by regulation of
x. In the Co-substituted Fe-B-R base permanent magnets
according to the present invention, the total composition of
B, R and (Fe plus Co) is essentially identical with that of
the Fe-B-R base alloys (without Co).
Boron (B) shall be used on the one hand in an amount no
less than 2 % so as to meet a coercive force of 1 kOe or
higher and, on the other hand, in an amount of not higher than
28 % so as to exceed the residual magnetic flux density Br of
about 4 kG of hard ferrite. R shall be used on the one hand
in an amount no less than 8 % so as to obtain a coercive force
of 1 kOe or higher and, on the other hand, in an amount of 30
% or less since it is easy to burn, incurs difficulties in
handling and preparation, and is e~pensive.
The present invention offers an advantage in that less
expensive light-rare earth element occurring abundantly in
nature can be used as R since Sm is not necessarily requisite
nor necessarily requisite as a main component.
The rare earth elements used in the magnetic materials
and the permanent magnets according to the present invention
include light- and heavy-rare earth elements inclusive of Y,
and may be applied alone or in combination. Namely, R
includes Nd, Pr, La, Ce, Tb, Dy, Ho, Er, Eu, Sm, Gd, Pm, Tm,
Yb, Lu and Y. Preferably, the light rare earth elements
amount to no less than 50 at % of the overall rare earth
elements R, and particular preference is given to Nd and Pr.
More preferably Nd plus Pr amounts to no less than 50 at % of
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the overall R. Usually, the use of one rare earth element
will suffice, but, practically, mixtures of two or more rare
earth elements such as mischmetal, didymium, etc. may be used
due to their ease in avilability. Sm, Y, La, Ce, Gd and the
like may be used in combination with other rare earth elements
such as Nd, Pr, etc. These rare earth elements R are not
always pure rare earth elements and, hence, may contain
impurities which are inevitably entrained in the production
process, as long as they are technically available.
Boron represented by B may be pure boron or ferroboron,
and those containing as impurities Al, Si, C etc. may be used.
Having a composition of 8 - 30 at % R, 2 - 28 at % B,
50 at % or less Co, and the balance Fe with the substantially
tetragonal system crystal structure after sintering and a mean
crystal grain size of 1 - 100 ~m, the permanent magnets
accordi~g to the present invention have magnetic properties
such as coercive force Hc of 2 1 kOe, and residual magnetic
flux density Br of ~ 4 kG, and provide a maximum energy
product (BH)max value which is at least equivalent or superior
to the hard ferrite (on the order of up to 4 MGOe). Due to
the presence of Co in an amount of 5 ~ or more the thermal
coefficient of Br is about 0.1 %/ C or less. If R ranges from
12 to 24 %, and B from 3 to 27 %, (BH)max 2 about 7 MGOe is
obtainable so far as R and B concern.
When the light rare earth elements are mainly used as R
(i.e., those elements amount to 50 at % or higher of the
overall R) and a composition is applied of 12 - 24 at % R, 4 -
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24 at % B, 5 - 45 at ~ Co, with the balance being Fe, maximum
energy product ~BH)max of 2 10 MGOe and said thermal
coefficient of Br as above are attained. These ranges are
more preferable, and (BEl)max reaches 33 MGOe or higher.
Referring to the Fe-5Co-B-R system for instance, the
ranges surrounded with contour lines of (BH)max 10, 20, 30 and
33 MGOe in Fig. 12 define the respective energy products. The
Fe-20Co-B-R system can provide substantially the same results.
Compared with the Fe-B-R ternary magnets, the
Co-containing Fe-B-R base magnets of the present invention
have better resistance against the temperature dependency,
substantially e~uivalent Br, equivalent or slightly less iHc,
and equivalent or higher (BH)max since the loop squareness or
rectangularity is improved due to the presence of Co.
Since Co has a corrosion resistance higher than Fe, it
is possible to afford corrosion resistance to the Fe-B-R base
.,
magnets by incorporation of Co. Particularly Oxidation
resistance will simplify the handling the powdery materials
and for the final powdery products.
As stated in the foregoing, the present invention
provides embodiments of magnetic materials and permanent
magnets which comprise 8 to 30 at % R (R representing at least
one of rare earth element including yttrium), 2 to 28 at ~ B,
50 at % or less Co (except that the amount of Co is zero), and
the balance being Fe and impurities which are inevitably
entrained in the process of production (referred to "Fe-Co-B-R
type n -
.
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The present invention provides further embodiments
which contain one or more additional elements M selected from
the group given below in the amounts of no more than the
values specified below wherein when two or more elements of M
are contained, the sum of M is no more than the maximum value
among the values specified below of said elements M actually
added and the amount of M is more than zero:
4.5 % Ti,8.0 % Ni,5.0 ~ Bi,
9.5 % V,12.5 % Nb,10.5 % Ta,
8.5 % Cr,9.5 % Mo,g.5 % W,
8.0 ~ Mn,9.5 % Al,2.5 % Sb,
7.0 % Ge,3.5 % Sn,5.5 % Zr,
and 5.5 % Hf.
The incorporation of the additional elements M enhances
Hc resulting in an improved loop squareness.
The allowable limits of typical impurities contained in
the final or finished products of magnetic materials or
magnets are up to 3.5, preferably 2.3, at % for Cu; up to 2.5,
preferably 1.5, at % for S; up to 4.0, preferably 3.0, at %
for C; up to 3.5, preferably 2.0, at % for P; and at most 1 at
%.for O ~oxygen), with the proviso that the total amount
thereof is up to 4.0, preferably 3.0, at ~. Above the upper
limits, no energy product of 4 MGOe is obtained, so that such
magnets as contemplated in the present invention are not
obtained (see Fig. 11). With respect to Ca, Mg and Si, they
are allowed to exist each in an amount up to about 8 at ~,
preferably with the proviso that their total amount shall not
1315571
- 20 ~
excee~ about 8 at ~. It is noted that, although Si has ef~ect
upon increases in Curie point, its amount is preferably about
8 at % or less, since iHc decreases sharply in an amount
exceeding 5 at %. In some cases, Ca and Mg may abundantly be
s contained in R raw materials such as commercially available
Neodymium or the like.
Iron as a starting material for instance includes
following impurities (by wt %) not exceeding the values below:
0.03 C, 0.6 Si, 0.6 Mn, 0.5 P, 0.02 S, 0.07 Cr, 0.05 Ni, 0.06
Cu, 0.05 Al, 0 05 2 and 0.003 N2.
Electrolytic iron generally with impurities as above mentioned
of 0.005 wt % or less is available.
Impurities included in starting ferroboron (19 - 13 %
B) alloys are not exceeding the values below, by wt %:
1~ 0.1 C, 2.0 Si, 10.0 Al, etc.
Starting neodymium material includes impurities, e.g.,
other rare earth element such as La, Ce, Pr and Sm; Ca, Mg,
Til Al, O, C or the like; and further Fe, C1, F or Mn
depending upon the refining process.
The permanent magnets according to the present
invelltion are prepared by a so-called powder metallurgical
process, i.e., sintering, and can be formed into any desired
shape and size, as already mentioned. However, desired
practical permanent magnets (bodies) were not obtained by such
a melt-quenching process as applied in the preparation of
amorphous thin film alloys, resulting in no practical coercive
force at all.
.
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On the other hand, no desired magnetic properties
(particularly coercive force) were again obtained at all by
melting, casting and aging used in the production of alnico
magnets, etc.. The reason is presumed to be that crystals
having a coarser grain size and a ununiform composition are
oDtained. Other various techniques have been attempted, but
none have given any results as contemplated.
In accordance with the present invention, however,
practical permanent magnets (bodies) of any desired shape are
obtained by forming and sintering powder alloys, which magnets
have the end good magnetic properties and mechanical strength.
For instance, the powder alloys are obtainable by melting,
casting and grinding or pulverization.
The sintered bodies can be used in the as-sintered
state as useful permanent magnets, and may of course be
subjected to aging as is the case in the conventional magnets.
The foregoing discussions also hold for both the
Fe-Co-B-R system and the Fe-Co-B-R-M system.
PREPARATION OF MAGNETIC MATERIALS
Typically, the magnetic materials of the present
invention may be prepared by the process forming the previous
stage of the overall process for the preparation of the
permanent magnets of the present invention~ For example,
various elemental metals are melted and cast into alloys
having a tetragonal system crystal structure, which are then
finely ground into fine powders.
.
- 22 _ 1 31 5571
As the magnetic material use may be made of the powdery
rare earth oxide R2O3 (a raw material for R). This may be
heated with powdery Fe, powdery Co, powdery FeB and a reducing
agent (Ca, etc) for direct reduction. The resultant powder
alloys show a tetragonal system as well.
The powder alloys can further be sintered into magnetic
materials. This is true for both the Fe-Co-B-R base and the
Fe-Co-B-R-M base magnetic materials.
The Fe-Co-B-R base magnets of the present invention
will now be explained with reference to the examples, which
are given for the purpose of illustration alone, and are not
intended to limit the invention.
Fig. 1 typically illustrates changes in Curie point Tc
of 77Fe-8B-15Nd wherein part of Fe is substituted with Co(x),
and (77-x)Fe-xCo-8B-15Nd wherein x varies from 0 to 77. The
samples were prepared in the following steps.
(1) Alloys were melted by high-frequency melting and cast
in a water-cooled copper mold. As the starting materials for
Fe, B and R use was made of, by weight ratio ~or the purity,
99.9 % electrolytic iron, ferroboron alloys of 19.38 % B, 5.32
% Al, 0.74 g Si, 0~03 % C and the balance Fe, and a rare earth
element or elements having a purity of 99.7 % or higher with
the impurities being mainly other rare earth elements,
respectively. As Co, electrolytic Co having a purity of 99.9
% was used.
(2) Pulverization : The castings were coarsely ground in a
stamp mill until they pass through a 35-mesh sieve, and then
,.
- 23 - 1 31 5571
finely pulverized in a ball mill for 3 hours to 3 - 10 ~m.
(3) The resultant pow~ers were oriented in a magnetic field
of 10 kOe and compacted under a pressureof 1.5 t/cm2.
(~) The resultant compacts were sintered at 1000 - 1200 ~C
for about one hour in an argon atmosphere and, thereafter,
allowed to cool.
Blocks weighing about 0~1 g were obtained from the
sintered bodies by cutting, and measured on their Curie points
using a vibrating sample magnetometer in the following manner.
A magnetic field of 10 kOe was applied to the samples, and
changes in 4~I depending upon temperature were determined in a
temperature range of from 250C to 800 C. A temperature at
which 4~I reduced virtually to zero was taken as Curie point
Tc.
In the above-mentioned systems, Tc increased rapidly
with the increase in the amount of Co replaced for Fe, and
exceeded 600C in Co amounts of no less than 30 ~.
In the permanent magnets, increases in Tc are generally
considered to be the most important factor for reducing the
changes in the magnetic properties depending upon temperature.
To ascertain this point, a number of permanent magnet samples
as tabulated in Table 1 were prepared according to the
procedures as applied for the preparation of those used in Tc
measurements to determine the temperature dependency of Br.
(5) The changes in Br depending upon temperature were
measured in the following manner. Magnetization curves are
obtained at 25 C, 60 C and 100C, respectively, using a BH
- 24 - 1315571
tracer, and the changes in Br at between 25 and 60~C and
between 60 and 100C were averaged. Table l shows the thermal
coefficient of Br and the measurement results of magnetization
curves at 25~C, which were obtained of various Fe-B-R and
5 Fe-Co-B-R base magnets.
From Table l, it is evident that the changes in Br
depending upon temperature are reduced by incorporation of Co
into the Fe-B-R base magnets. Namely, thermal coefficients of
about 0.1 ~/ C or less are obtained if Co is 5 % or more.
Table 1 also shows the magnetic properties of the
respective samples at room temperature.
In most of the compositions, iHc generally decreases
due to the Co substitution, but (B~l)max increases due to the
improved loop rectangularity of the magnetization curves.
1~ However, iHc decreases if the amount of Co increases from 25
to 50 ~% finally reaching about the order of 1.5 kOe.
Therefore the amount of Co shall be no higher than 50 ~ 50 as
to obtain iHc ~ 1 kOe suitable for permanent magnets.
From Table l and Fig. l the relationship between the Co
amount and the magnetic properties is apparent. Namely, even
a small amount of Co is correspondingly effective for the
improvement of Tc. In a range of 25 % or less Co, other
magnetic properties (particularly, the energy product) are
substantially not affected. (See, samples *2, and 8 - 12 of
Table l). If Co exceeds 25 %, (BH)max also decreases.
The reasons already given in connection with the upper
and lower limits of B and the lower limit of R will be
con~irmed from Table l, Fig. 2 and Fig. 3.
- 25 - 1315571
Table 1
_ then~
No. composit ons oo~e~i,t i~ ~Ce¦ Br(kG) (HH)m~x i
*1 Fe-2B-15Nd 0.14 1.0 9.6 4.0
*2 Fe-8B-15Nd 0.14 7.3 12.1 32.1
*3 Fe-17B-lSNd 0.15 7.6 8.7 17.6
*4 Fe-17B-30Nd 0.16 14.8 4.5 4.2
*5 Fe-20Co-15Nd _ O O O
*6 Fe-lOCo-19B-SPr _ O O O
*7 Fe-60Co-8B-15Nd 0.05 0.8 8.2 3.5
8 Fe-lOCo-8B-15Nd 0.09 5.2 12.0 33.0
9 Fe-20Co-8B-15Nd 0.07 8.8 12.0 33.1
Fe-30Co-8B-15Nd 0.06 4.5 12.0 24.2
11 Fe-4OCo-8B-15Nd 0.06 3.1 11.8 17.5
12 Fe-50Co-8B-15Nd 0.06 1.5 8.7 7.7
13 Fe-15Co-17B-15Nd 0.10 ¦ 7.4 8.9 18.2
14 Fe-30Co-17B-15Nd 0.08 6.3 8.6 16.5
Fe-2000-8B,lOTb,3Ce O.08 6.1 6.3 8.8
16 Fe-20Co-12B-14Pr 0.07 7.2 10.5 25.0
17 Fe-15Co-17B-8Nd-5Pr O.08 7.4 8.3 15.7
18 Fe-20Cb-1 ~ 3 ~ 13Pr O.07 6.5 9.6 17.5
19 Fe-10Go-15B-8Nd-7Y O.O9 6.0 7.5 ~.O
Fe-10Co-14B-7Nd-3Pr O.O9 6.8 7.8 14.2
Zl Fe-30Co-17B-28Nd 0.09 12.2 4.6 4.7
N.B. :prefix * refers to comparative tests
.
..
,
- 26 - 1 31 5571
As a typical embodiment of the sintered magnetic
magnets of the Fe-Co-B-R system in which part of Fe is
substituted with Co, Fig. 2 shows an initial magnetization
curve 1 for 57Fe-20Co-8B-15Nd at room temperature.
The initial magnetizaton curve 1 rises steeply in a low
magnetic field, and reaches saturation. The demagnetization
curve 2 shows very high loop rectangularity, which indicates
that the magnet is a typical high-performance anisotropic
magnet. From the form of the initial magnetization curve 1,
it is thought that this magnet is a so-called nucleation ~ype
permanent magnet since the SmCo type magnets of the nucleation
type shows an analogous curve, wherein the coercive force of
which i8 determined by nucleation occurring in the inverted
magnetic domain. The high loop rectangularity of the
lS demagnetization curve 2 indicates that this mgnet is a typical
high-performance anisotropic magnet. Other samples according
to the present invention set forth in Table 1 all showed
magnetization curves similar to that of Fig. 4.
A number of magnets using primarily as R light-rare
earth element such as Nd, Pr, etc., are shown in Table 1, from
which it is noted that they possess high magnetic properties,
and have their tempPrature dependency further improved by the
substitution of Fe with Co. It is also noted that the use of
a mixture of two or more rare earth element as R is also
useful.
Permanent magnet samples of Fe-Co-B-R-M alloys
.
. . .
- 27 - 1 31 557 t
containing as ~1 one or two additional elements were prepared
in a manner similar to that applied for the preparation of the
F~e-Co-B-R base magnets.
The additional elements M used were Ti, Mo, Bi, Mn, Sb,
Ni, Sn, Ge and Ta each having a purity of 99 %, by weight so
far as the purity concerns as hereinbelow, W having a purity
of 98 %, Al having a purity of 99.9 %~ and Hf having a purity
of 95 %. As V ferrovanadium containing 81.2 % of V; as Nb
ferroniobium containing 67.6 % of Nb; as Cr ferrochromium
containing 61.9 % of Cr; and as Zr ferrozirconium containing
75.5 % of Zr were used, respectively.
A close examination of the samples having a variety of
compositions was carried out by the determination of iHc, Br,
(~H~max, etc~ ~s a result, it has been found that, in
1~ quintinary or multicomponent systems based on Fe-Co-B-R-M
(wherein M represents one or two or more additional elements),
there is a certain region in which high permanent magnet
properties are developed.
Table 2 shows the maximum energy product (BH)max,
which is the most important factor of the permanent magnet
properties, of typical samples. In Table 2, Fe is the
balance.
From Table 2, it has been appreciated that the
Fe-Co-B-R-M base magnets have high energy product of 10 MGOe
or greater over a wide compositional range.
This table mainly enumerates the examples of alloys
containing Nd and Prl but any of 15 rare earth element (Y, La,
I'J ~
- 28 - 1 31 5571
Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) give rise
to increase in (BH)max. However, the alloys containing Nd and
Pr according to the present invention are more favorable than
those containing as the main materials other rarer rare earth
element (Sm, Y and heavy-rare element), partly because Nd and
Pr occur relatively abundantly in rare earth ores, and
especially because no applications of Nd in larger amounts
have been found.
Also in the Fe-Co-B-R-M alloys, Co has no noticeable
infiuence upon (BH)max, when it is added in an amount of 25 ~
or less and Co contributes to the increase in the Curie points
with the increasing Co amount as is the case for the Fe-Co-B-R
alloys. For instance, comparisons of Sample Nos. 48 with 50,
5~ with 60, and 68 with 70 reveal that a compositional
1~ difference in the amount of Co (1 to 10 Co) between these
alloys causes no noticeable difference in tBH)max. Fig. 5
shows the relationship between the Curie point and the amount
of Co (by at %) of the Fe-Co-B-R-M alloys wherein M is V, Nb,
Zr and Cr, and indicates that the Curie point increases with
increases in the amount of Co, but the addition of M gives
rise to substantially no remarkable change in the Curie point.
Parallel tendencies have been observed in the
Fe-Co-B-R-M fundamental alloys regardless of the type of R.
Even a slight amount of Co, e.g., 1 % is effective for Tc
increases, and it is possible to obtain alloys having any
desired Tc between about 310 C and about 750C by varying of
x, as will be evi~ent from the (76 - x) Fe-xCo-8B-15Nd-l~
- 29 -
1315571
system exemplified in Fig. S.
Accordingly, it has turne~ out that with respect to the
Fe-Co-B-R-M system the relationships between the Co amount and
the magnetic properties, and between the ranges of B and R and
the magnetic properties are established analogously to the
Fe-Co-B-R system previously discussed, provided that the
effect of the additional elements M acts additionally.
The Fe-Co-B-R-M magnets according to the present
invention have Curie points higher than the Fe-B-R-M magnets
without Co.
In the Fe-Co-B-R-M magnets, most of M have an effect
upon increases in Hc. Fig. 6 shows the demagnetization curves
of the typical examples of the Fe-Co-B-R-M ma~nets and M-free
~e-Co-B-R magnets given for the purpose of comparison. In
lS this figure, reference numerals 1 to 3 denote the
demagnetization curves of a M-free magnet, a Nb-containing
magnet (Table 1 No.3) and a W-containing magnet ~Table 1 No.
83), respectively.
An increase in ~c due to the addition of M provides an
increased stability and wide applicability of the permanent
magnets. However, the greater the amount of ~1, the lower the
Br and (BH)max will be, due to the fact that they are
nonmagnetic materials (except Ni). Since permanent magnets
having slightly reduced (BH)max but high Hc have recently been
often required in certain fields, the addition of M is very
useful, however, provided that (BH)max is at least 4 MGOe.
To ascertain the effect of M upon Br, Br was measured
~ ,.
_ 30 - t 31 5571
in varied amounts of M. The results are summarized in Figs. 7
to 9. ~s seen from Figs. 7 to 9, the upper limits of the
additional elements M (Ti, Zr, Hf, V, Ta, ~b, Cr, W, Mo, Sb,
Sn, Ge and Al) other than Bi, Ni, and Mn may be chosen such
that Br is at least equivalent to about 4 kG of hard ferrite.
A preferable range in view of Br should be appreciated from
Figs. 7 to 9 by defining the Br range into 6.5 kG, 8~G, 10 kG
or the like stages.
Based on these figures, the upper limits of the amounts
of additional elements M are fixed at the following values at
or below which (BH)max is at least equivalent or superior to
about 4 MGOe of hard ferrite:
4.5 % Ti,8.~ % Ni,5.0 % Bi,
9.5 % V,12.5 % Nb,10.5 % Ta,
8.5 % Cr,9.5 % Mo,9.5 % W,
8.0 % Mn,9.5 % Al,2.5 ~ Sb,
7.0 ~ Ge,3.5 % Sn,5.5 % Zr,
and 5.5 ~ Hf.
When two or more elements M are employed, the resulting
characteristic curve will be depicted between the
characteristic curves of the individual elements in Fig. 7 to
9. Thus each amount of the individual elements M are within
each aforesaid range, and the total amount thereof is no more
than the maximum values among the values specified for the
individual elements which are actually added and present in a
system~ For instance, if Ti, V and Nb are addednt, the total
amount of these must be mo more than 12.5% in all.
- 31 - 1 31 5 571
A more preferable range for the amount of M is
determined from a range of (BH)max within which it exceeds 10
r~;Goe of the highest grade alnico. In order that ~B~)max is no
less than 10 MGOe, sr of 6.5 kG or higher is required.
From Figs. 7 to 9, the upper limits of the amounts of M
are preferably defined at the following values:
4.0 % Ti,6.5 % Ni, 5.0 % Bi,
8.0 ~ V,10.5 % Nb, 9.5 % Ta,
6.5 ~ Cr,7.5 ~ Mo, 7.~ ~ W,
6.0 % Mn,7.5 % Al, 1.5 % Sb,
5.5 % Ge,2.5 % Sn, 4.5 % Zr,
and 4.5 % Hf
wherein two or more additional elements M are used, the
preferable ranges for M are obtained when the individual
15 elements are no higher than the aforesaid upper limits, and
the total amount thereof is no higher than the maximum values
among the values allowed for the individual pertinent elements
which are actually added and present.
Within the upper limits of M, when the Fe-Co-B-R base
system preferably comprises 4 to 24 % of B, 11 to 24 % of R
(light-rare earth elements, primarily Nd and Pr), and the
balance being the given amounts of Fe and Co, ~BH)max of 10
MGOe or higher is obtained within the preferable ranges of the
additional elements M, and reaches or exceeds the (BH)max
level of hard ferrite within the upper limit of M.
Even when the Ee-Co-B-R base system departs from the
above-mentioned preferable range, (BH~max exceeding that of
s~ .
-32-131557~
hard ferrite is obtained, if the additional element M are in
the above-mentioned preferable range. According to more
preferable embodiments of the present invention, the permanent
magnets have (BH)max of 15, 20, 25, 30 and even 33 MGOe or
higher.
In general, the more the amount of M, the lower the Br;
however, most elements of M serve to increase iHc. Thus,
(BH)max assumes a value practically similar to that obtained
with the case where no M is applied, through the addition of
an appropriate amount of M, and may reach at most 33 MGOe or
higher. The increase in coercive force serves to stabilize
the magnetic properties, so that permanent magnets are
obtained which are practically very stable and have a high
energy product.
If large amoùnts of Mn and Ni are incorporated, iHc
will decrease; there is only slilght decrease in Br due to the
fact that Ni is a ferromagnetic element (see Fig. 8).
Therefore, the upper limit of Ni is 8 %, preferably 6.5 ~, in
view of Hc.
The effect of Mn upon decrease in Br is not strong but
~larger than is the case with Ni~ Thus, the upper limit of Mn
is 8 ~, preferably 6 %, in view of iHc.
With respect to Bi, its upper limit shall be 5 %, since
any alloys having a Bi content exceeding 5 % cannot
practically be produced due to extremely high vapor pressure.
- 33 - 1 31 5571
Table 2 - 1
s~ e ~o compositions (at %)
_ Fe-2Co-8B-15Nd-2AQ 29.5
2 Fe-5Co-8B-15Nd-0.5AQ 35.2
3 Fe-5Co-17B-15Nd-4AQ 11.5
4 Fe-lOCo-17B-17Nd-0~5AQ 12.7
Fe-lOCo-8B-15Nd-lAQ 31.6
6 Fe-20Co-8B-12Nd-0.5AQ 23.0
7 Fe-35Co-6B-24Nd-5AQ 10.5
8 Fe-5Co-17B-15Nd-2.5Ti 11.0
9 Fe-lOCo-13B-14Nd-2Ti 18.1
Fe-20Co-12B-16Nd-lTi ., 22.1
11 Fé-35Co-8B-15Nd-0.5Ti 20.5
12 Fe-35Co-6B-25Nd-0.3Ti 12.4
13 Fe-2Co-8B-16Nd-2V 24.0
14 Fe-5Co-6B-15Nd-0.3V 31.1
Fe-5Co-8B-14Nd-6V 16.3
16 Fe-lOCo-17B-15Nd-lV 14.8
17 Fe-20Co-8B-12Nd-0.5V 21.6
18 Fe-20Co-15B-17Nd-lV 17.2
19 Fe-35Co-6B-25Nd-lV 15.2
Fe-2Co-8B-16Nd-2Cr 22.4
~ 34 1 31 557
Table 2 - 2
n~. compositions (at %) (MGOe)
21 Fe-5Co-20B-15Nd-0.5Cr 12.0
22 Fe-5Co-7B-14Nd-4Cr 18.1
23 Fe-lOCo-8B-15Nd-0~5Cr 32.7
24 Fe-lOCo-17B-12Nd-0.2Cr 17.2
Fe-20Co-8B-15Nd-0.5Cr 31.7
26 Fe-20Co-8B-15Nd-lCr 30.5
27 Fe-35Co-6B-25Nd-lCr 14.7
28 Fe-2Co-8B-13Nd-0.5Mn 30.1
29 Fe-5Co-7B-14Nd-lMn 25.1
Fe-lOCo-9B-lSNd-lMn . , 21.0
31 Fe-20Co-8B-16Nd-lMn 24.9
32 Fe-20Co-16B-14Nd-0.2Mn 17.1
33 Fe-20Co-7B-14Nd-4Mn 14.5
34 Fe-35Co-9B-20Nd-lMn 14.2
Fe-5Co-8B-15Nd-lZr 32.3
36 Fe-lOCo-9B-14Nd-lZr 32.2
37 Fe-lOCo-17B-16Nd-6Zr 12.9
38 Fe-lOCo-6B-20Nd-0.5Zr 18.1
39 Fe-20Co-8B-12Nd-O.SZr 25.6
Fe-20Co-20B-14Nd-0.3Zr 13.2
~ 35 ~ 1 31 557
Table 2 - 3
sample No. compositions (at %) ~Oe¦
41 Fe-35Co-6B-20Nd-lZr 16.0
42 Fe-5Co-8B-15Nd-lHf 32.2
43 Fe-lOCo-9B-14Nd-lHf 32.0
44 Fe-lOCo-17B-16Nd-6Hf 13.1
Fe-20Co-8B-12Nd-0.5Hf 17.9
46 Fe-20Co-20B-14Nd-0.3Hf 25.2
47 Fe-35Co-6B-20Nd-lHf 15.7
48 Fe-lCo-8B-16Nd-0.5Nb 33.3
49 Fe-2Co-8B-14Nd-lNb 35.5
Fe-lOCo-8B-15Nd-0.5Nb ~ 33.4
51 Fe-lOCo-7B-14Nd-lNb 33.1
, 52 Fe-20Co-9B-14Nd-0.5Nb 33.1
53 Fe-20Co-8B-15Nd-lNb 31.3
54 Fe-20Co-17B-13Nd-6Nb 10.7
Fe-20Co-8B-15Nd-8Nb 14.8
56 Fe-20Co-6B-25Nd-lNb 16.8
57 Fe-35Co-7B-15Nd-3Nb 21.6
58 Fe-lCo-8B-16Nd-0.5Ta 32.5
59 Fe-2Co-8B-14Nd-lTa 31.5
Fe-lOCo-8B-15Nd-0.5Ta 32.3
_
.~ .
- 36 - 1 31 5571
Table 2 - 4
sample No. compositions (at %) (BH)max
61 Fe-lOCo-7B-14Nd-lTa 31.2
62 Fe-20Co-9B-14Nd-0.5Ta 31.5
63 Fe-20Co-7B-16Nd-lTa 30.3
64 Fe-20Co-15B-13Nd-6Ta 10.5
Fe-20Co-8B-15Nd-8Ta 11.6
66 Fe-20Co-6B-25Nd-lTa 15.6
67 Fe-35Co-7B-15Nd-3Ta 20.0
68 Fe-lCo-8B-15Nd-0.5Mo 35.1
69 Fe-2Co-8B-15Nd-lMo 34.7
Fe-lOCo-8B-16Nd-0.5Mo'' 33.0
71 Fe-lOCo-7B-14Nd-lMo 31.0
72 Fe-2aCo-9B-14Nd-0.5Mo 31.0
73 Fe-20Co-6B-16Nd-lMo 32.2
74 Fe-20Co-17B-13Nd-2Mo 14.6
Fe-20Co-8B-13Nd-6Mo 14.3
76 Fe-20Co-6B-25Nd-lMo 16.4
_ 77 Fe-35Co-7B-15Nd-3Mo 18.8
78 Fe-lCo-8B-15Nd-0.5W 33.6
79 Fe-2Co-8B-16Nd-lW 33.2
Fe-lOCo-8B-16Nd-0.5W 33.7
- 37 - 1 31 5571
Table 2 - 5
sample No. compositions (at %) (BH)max
.__
81 Fe-lOCo-7B-14Nd-lW 33.3
82 Fe-20Co-9B-14Nd-0.5W 32.5
83 Fe-20Co-8B-15Nd-lW 32.4
84 Fe-20Co-17B-13Nd-2W 14.5
Fe-20Co-8B-13Nd-6W 16.2
86 Fe-20Co-6B-25Nd-lW 16.0
87 Fe-35Co-?B-15Nd-3W 18.4
88 Fe-5Co-8B-15Nd-lGe 22.2
89 Fe-lOCo-9B-14Nd-2Ge 11.4
Fe-lOCo-17B-16Nd-0.5Gè ~14.2
91 Fe-20Co-6B-20Nd-0.5Ge 17.2
.92 Fe-20Co-8B-12Nd-0.3Ge25.3
93 Fe-20Co-20B-14Nd-0.5Ge10.5
94 Fe-35Co-6B-20Nd-lGe 10.1
Fe-5Co-8B-15Nd-lSb 13.2
96 Fe-lOCo-9B-14Nd-0.5Sb15.4
_ 97 Fe-lOCo-17B-16Nd-lSb 11.1
98 Fe-20Co-6B-20Nd-O.lSb21.2
99 Fe-20Co-8B-12Nd-1.2Sb12.0
100 Fe-20Co-20B-14Nd-0.5Sb10.5
- 38 - 1 31 5571
Table 2 - 6
sample No. compositions (at ~) ~U)
101 ~e-35C~-~B~ d-0.5s~ 10.2
102 Fe-5Co-8B-lSNd-lSn 20.2
103 Fe-lOCo-9B-14Nd-0.5Sn 26.1
104 Fe-lOCo-17B-16Nd-0.5Sn 11.2
105 Fe-20Co-6B-20Nd-0.5Sn 15.1
106 Fe-20Co-8B-12Nd-lSn 15.0
107 Fe-20Co-20B-14Nd-0.5Sn 10.4
108 Fe-35Co-6B-20Nd-0.5Sn 10.9
109 Fe-5Co-8B-15Nd-0.2Bi 31.5
110 Fe-lOCo-9B-14Nd-Q.5Bi~, 29.6
111 Fe-lOCo-17B-16Nd-lBi 16.0
112 Fe-20Co-6B-20Nd-3Bi 15.8
113 Fe-20Co-8B-12Nd-1.5Bi 21.9
114 Fe-20Co-20B-14Nd-lBi 10.9
115 Fe-35Co-6B-20Nd-0.5Bi 18.2
116 Fe-5Co-8B-15Nd-lNi 24.3
117 Fe-lOCo-9B-14Nd-4Ni 17.1
118 Fe-lOCo-17~-16Nd-0.2Ni 16.2
119 Fe-20Co-6B-20Nd-5Ni 15.8
120 Fe-20Co-8B-12Nd-0.5Ni 25.3
- 39 - 1 31 5571
Table 2 - 7
~ample No. compositions (at %) ¦MGOe)
.
121 Fe-20Co-20B-14Nd-lNi 15.3
122 Fe-35Co-6B-20Nd-3Ni 15.3
123 Fe-5Co-8B-15Pr-lAQ 24.8
124 Fe-lOCo-9B-14Pr-lW 26~5
125 Fe-5Co-17B-14Pr-2V 10.7
126 Fe-lOCo-8B-16Pr-0.5Cr 23.2
127 Fe-20Co-8B-17Pr-0.5Mn 21.3
128 Fe-20Co-8B-15Pr-lZr 25.4
129 Fe-lOCo-7B-14Pr-lMo-lZr 20.3
130 Fe-lOCo-7B-14Nd-0.5AQ-lV , 29.1
131 Fe-lOCo-9B-15Nd-2Nb-0.5Sn 22.8
, 132 Fe-2OCo-8B-16Nd-lCr-1Ta-0.5AQ22.5
133 Fe-20 ~ 8B-14Nd-~0.5W~0. ~22.1
134 Fe-20Co-15B-15Pr-0.5Zr-0.5Ta-0.5Ni 10.9
135 Fe-lOCo-17B-lONd-5Pr-0.5W 16.2
136 Fe-lOCo-8B-8Nd-7Ho-lAQ 19.9
137 Fe-lOCo-7B-9Nd-5Er-lMn 20.1
138 Fe-5Co-8B-lONd-5Gd-lCr 21.5
139 Fe-lOCo-9B-lONd-5La-lNb 19.3
140 Fe-20Co-lOB-lONd-5Ce-0.5Ta 20.1
141 Fe-20Co-7B-llNd-4Dy-lMn 19.5
- ~o - 1 31 5571
The relationship between the crystal grain size and the
magnetic properties of the Fe-Co-B-R base magnets will be
described in detail hereinbelow.
The pulverization procedure as previously mentioned was
5carried out for varied periods of time selected in such a
manner that the measured mean particle sizes of the powder
ranged from 0.5 to lO0 ~m. In this manner, various samples
having the compositions as specified in Table 3 were obtained.
Comparative Examples : To obtain a crystal grain
10size of lO0 ~m or greater, the sintered bodies were
maintained for prolonged time in an argon atmosphere at
a temperature lower than the sintered temperature by 5
- 20C.
From the thus prepared samples having the compositions
15as specified in Table 3 were obtained magnets which were
studied to determine their magnetic properties and their mean
crystal grain sizes. The results are set forth in Table 3.
The mean crystal grain size referred to herein was measured in
the following manner:
20The samples were polished and corroded on their
surfaces, and photographed through an optical microscope at a
magnification ranging from xlO0 to xlO00. Circles having
known areas were drawn on the photographs, and divided by
lines into eight equal sections. The number of grains present
25on the diameters were counted and averaged. However, grains
on the borders (circumferences) were counted as half grains
(this method is known as Heyn's method). Pores were omitted
- 1- 13l557l ,
from calculation.
In Table 3, the samples marked * represent comparative
examples.
From the sample Nos. *7 and *8, it is found that Hc
drops to less 1 kOe if the crystal grain size departs from the
scope as defined in the present invention.
Samples designated as Nos. 13 and 16 in Table 3 were
studied in detail in respect of the relationship between their
mean crystal grain size D and Hc. The results are illustrated
in Fig. 10, from which it is found that Hc peaks when D is
approximately in a range of 3 - 10 ~m, decrease steeply when D
is below that range, and drops moderately when D is above that
range. Even when the composition varies within the scope as
defined in the present invention, the relationship between the
lS mean crystal grain size D and Hc is substantially maintained.
This indicates that the Fe-Co-B-R system magnets are the
single domain particle type magnets.
~rom the results given in Table 3 and Fig. 10, it is
evident that, in order for the Fe-Co-B-R base magnets to
possess Br of about 4 kG of hard ferrite or more and Hc of no
less than 1 kOe, the composition comes within the range as
defined in the present invention and the mean crystal grain
size D is 1 - 100 ~m, and that, in order to obtain Hc of no
less than 4 kOe, the mean crystal grain size should be in a
range of 1.5 - 50 ~m.
Control of the crystal grain size of the sintered
compact can be carried out by controlling process conditions
such as pulverization, sintering, post heat treatment, etc.
.; .
- 42 - 1 31 5571
Tal: le 3
_ magnetic prop~ties
~ean crystal then~l
No c~rpositions (at %) grain size coefficient iNc(JcOe) ~r(lsG) (~H)IIBX
*1 Fe-2B-15Nd 6 . O O .14 1.0 9.6 4.0
*2 Fe-8B-lSNd 5 . 5 0.14 9.5 12.3 33.2
*3 Fe-32B-15Nd 10 .1 O .1611.0 2.5 1.3
*4 Fe-17B-30Nd 7 . 3 O .1614.8 4.5 4.2
*5 Fe-lOCo-15B-5Pr 22 . O _ O O O
*6 Fe-60Co-lOB-13Nd 15 .7 O . 070.6 7.9 2.8
*7 Fe-20Co-12B-14Pr 110 O . 09~1 5.7 1.8
*8 Fé-40Co-17B-15Nd O . 85 O . 07< 1 6.1 1.4
9 Fe-20Co-12B-14Pr 8 . 8 O . 096.8 10.4 19.5
Fe-40Co-17B-15Nd 2 . 8 O . 066.5 9.2 17.1
11 Fe-50Co-8B-15Nd 4 . 7 O . 061.5 8.7 5.5
12 Fe-5Co-8B-15Nd 29 . O O .11 6.4 11.3 25.2
13 Fe-30Co-17B-15Nd 36 . 5 O . 085.2 8.6 13.6
14 Fe-15Co-16B-16Pr 68 . O O . 093.6 10.2 9.4
Fe-20Co--7B--15Nd5 . 6 O . 098.6 12.1 31.9
16 Fe--5Co--7B-15Nd 6 . 5 0.11 9.0 12.5 34.2
17 Fe--20Co--llB-8Nd-7Pr17 . 5 O . 096.3 9.5 14.7
Fe-10~11B 7N~I-
18 3Pr-5La22 . 3 O .10 4.8 7.7 9.8
19 Fe--30Co-17B-22Nd13 . 5 O . 084.4 5.4 4.8
Fe~ -lOB-5Hi~-lONd19 . O 0.10 6.6 8.9 15.7
21 Fe-lOCo lOB-13Nd--2~7-lLa 15 . 50.10 6.8 10.0 22.3
22 F~20~9B--lONd-6Pr-l~n10 . 3 O .105 . 7 10 . 4 21. 5
23 Fe-lSCo-7B-14Nd-2Gd 7 . S O .104 . 7 9 . 7 16 . 7
!
~ 43 - 1 31 5571
The embodiments and effects of the M-containing
Fe-Co-B-R base magnets (Fe-Co-B-R-M magnets) will now be
explained with reference to the following examples given for
the purpose of illustration alone and intended not to limit
S the invention .
Tables 4 - 1 to 4 - 3 show properties of the permanent
magnets comprising a variety of Fe-Co-B-R-M compounds, which
were prepared by melting and pulverization of alloys, followed
by forming of the resulting powders in a magnetic field then
sintering. Permanent magnets departing from the scope of the
present invention are also shown with mark *. It is noted
that the preparation of samples were substantially identical
with that of the Fe-Co-B-R base magnets.
From the samples having the compositions as shown in
Tables 4 - 1 to 4 - 3 were obtained magnets whose magnetic
properties and mean crystal grain size were measured. The
results are set out in Table 4 - 1 to 4 - 3.
- 44 - 1 3t 5 ~7
Table 4 - 1
No. compositions (at %) mlan crys ~ ~MGOe)
1 Fe-2Co-8B-15Nd-2AQ 4.8 29.5
2 Fe-30Co-17B-13Nd-4AQ 7.4 17.6
3 Fe-lOCo-13B-14Nd-2Ti 10.1 16.6
4 Fe-lOCo-13B-14Nd-2Ti 75.0 4.3
Fe-20Co-13B-16Nd-0.5Ti3.2 27.5
6 Fe-35Co-8B-20Nd-lTi 25.0 11.2
7 Fe-2Co-17B-16Nd-2V 55.0 8.3
8 Fe-20Co-12B-12Nd-0.5V 5.2 21.5
9 Fe-35Co-6B-20Nd-5V 13.5 10.7
10 Fe-5Co-7B-14Nd-3Cr 8.7 16.0
11 Fe-35Co-6B-23Nd-lCr 18.8 7.4
12 Fe-15Co-16B-15Nd-1.5Mn21.2 14.6
13 Fe-5Co-8B-17Nd-3Zr 37.5 23.1
14 Fe-lOCo-20B-15Nd-0.5Hf28.0 12.6
15 Fe-35Co-7B-2ONd-2Hf 11.2 15.4
16 Fe-3Co-8B-14Nd-lNb 5.0 36.0
17 Fe-lOCo-7B-17Nd-5Nb 10.7 18.8
18 Fe-5Co-15B-14Nd-lTa 16.2 11.4
19 Fe-35Co-7B-15Nd-3Ta 7.6 20.8
20 Fe-2Co-8B-lSNd-0.5No 6.5 33.5
-45-131557
Table 4 - 2
No. compositions (at ~) mean crys~ (BH)max
21Fe-lOCo-9B-14Nd-2~1o 9.2 28. 5
22 Fe-20Co-17B-15Nd-2Mo26.2 22.4
23 Fe-20Co-17B-14Nd-6Mo15 . 7 14.7
24 Fe-20Co-7B-25Nd-lMo 9.5 15.4
Fe-35Co-8B-17Nd-3Mo 22.8 16.9
26 Fe-2Co-7B-17Nd-0.5W 11.2 32.2
27 Fe-5Co-12B-17Nd-3W 35.1 26.3
28 Fe-lOCo-8B-.14Nd-lW 3.8 35.4
29 Fe-20Co-17B-15Nd-lW 47.0 13.2
Fe-20Co-8B-14Nd-6W 27.3 14.8
31 Fe-35Co-7B-15Nd-3W 12.7 12.0
32 Fe-20Co-8B-14Nd-lGe 18.2 10.7
33 Fe-lOCo-9B-16Nd-0.5Sb9.7 17.8
34 Fe-20Co-17B-15Nd-lSn 6.0 18.8
Fe-20Co-6B-20Nd-3Bi 6.2 16.6
36 Fe-5Co-8B-15Nd-3Ni 16.8 14.8
37 Fe-20Co-lOB-17Nd-lNi 8.4 19.2
38 Fe-20Co-7B-16Nd-lCu 23.2 13.8
39 Fe-5Co-8B-15Px-lAQ 4.4 27.3
Fe-lOCo-lOB-17Pr-lW .... .... 26.4
- 46 - 1315571
Table 4 - 3
No. compositions (at ~)grain size D(~m) (BH)max
.
41 Fe-20Co-8B-15Pr-2Zr 4.6 25.4
42 Fe-lSCo-8B-lONd-5Pr-lNb-lW 7.3 2801
43 Fe-lOCo-7B-15Nd-lLa-lTa-0.5Mn12.3 17.8
44 Fe-20Co-12B-12Nd-3Ho-2W-0.5Hf 2.8 22.3
Fe-20Co-8B-llNd-4Dy-lAQ-0.5Cr14.1 18.6
46 Fe-lOCo-7B-lONd-5Gd-lW-0.5Cu 28.3 11.4
47 Fe-12Co-8B-13Nd-lSm-lNb .6.0 20.5
48 Fe-5Co-7B-14Nd-lCe-lMo 9.4 . 18.3
49 Fe-20Co-8B-13Nd-2Pr-lY-lAQ 12.5 22.3
~,,
~ . , '''' .
,
'
- 47 ~ 1 3 1 5 57 1
Table 5
_ ~ magnetic properties
mean crystal
No. compositions (at %) D (~m) iHc(kOe) Br(kG) (BH)max
*1 80Fe-20Nd lS 0 0 0
*2 53Fe-32B-lSNd 10 11.0 2.5 1.3
*3 48Fe-17B-35Nd - 4 >15 1.4 <1
*4 73Fe-lOB-17Nd 0.7 <1 5.0 <1
82Fe-5B-13Nd 140 <1 6.3 2.2
N.B.:prefix * refers to comparativ~ tests
- 48 ~ 1 31 557 1
Fig. 11 shows the demagnetization curves of the typical
examples of the invented Fe-Co-B-R-M base magnets and the
M-free Fe-Co-B-R base magnets. In this figure, reference
numerals 1 - 3 denote the demagnetization curves of a M-free
magnet, a Mo-containing magnet (Table 4 - 1 No. 20) and a
Nb-containing magnet (Table 4 - 1 No. 16), all of which show
the loop squareness useful for permanent magnet materials.
The curve 4 represents ones with a mean crystal grain
size D of 52 ~m for the same composition as 3.
In Table 5 comparative samples with marks * are shown,
wherein *l - *3 are samples departing from the scope of the
present invention.
From *4 and *5, it is found that Hc drops to 1 kOe or
less if the mean crystal grain size departs from the scope of
the present invention.
Samples designated as Nos. 21 and 41 in Tables 4 - 2
and 4 - 3 samples were studied in detail in respect of the
relationship between their mean crystal grain size D and Hc.
The results are illustrated in Fig. 11, from which it is found
that Hc peaks when D is approximately in a range of 3 - 10 ~m,
decreases steeply when D is below that range, and drops
moderately when D is above that range. Even when the
composition varies within the scope as defined in the present
invention, the relationship between the average crystal grain
size D and Hc is substantially maintained. This indicates
that the Fe-Co-B-R-M base magnets are the single domain
!
~ 49 ~ 1 31 557
particle type magnets.
Apart from the foregoing samples, an alloy having the
same composition as Sample No. 20 of Table 4 - 1 was prepared
by the (casting) procedure ~1) as already stated. However,
the thus cast alloy had Hc of less than 1 kOe in spite of its
mean crystal grain size being in a range of 20 - 80 ~m.
From the results given in Table 4 - 1 and Fig. 10, it
is evident that, in order for the Fe-Co-B-R-M base magnets to
possess Br of about 4 kG of hard ferrite or more and Hc of no
less than 1 kOe, the composition comes within the range as
defined in the present invention and the mean crystal grain
size is about 1 - about 100 ~m, and that, in order to obtain
Hc of no less than 4 kOe, the mean crystal grain size should
be in a range of about 1.5 - about 50 ~m.
Control of the crystal grain size of the sintered
compact can be controlled as is the case of the Fe-Co-B-R
system.
As mentioned in the foregoing, the invented permanent
magnets of the Fe-Co-B-R-M base magnetically anisotropic
sintered bodles may contain, in addition to Fe, Co, B, R and
M, impurities which are entrained therein in the process of
production as is the case ~or the Fe-Co-B-R system.
CRYSTAL STRUCTURE
It is believed that the magnetic materials and
permanent magnets based on the Fe-Co-B-R base alloys according
to the present invention can satisfactorily exhibit their own
- 50 ~ 1 31 5571
magnetic properties due to the fact that the major phase is
formed by the substantially tetragonal crystals of the Fe-B-R
type. As already discussed, the Fe-Co-B-R type alloy is a
novel alloy in view of its Curie point. As will be discussed
hereinafter, it has further been experimentally ascertained
that the presence of the substantially tetragonal crystals of
the Fe-Co-B-R type contributes to the exhibition of magnetic
properties. The Fe-Co-B-R type tetragonal system alloy is
unknown in the art, and serves to provide a vital guiding
principle for the production of magnetic materials and
permanent magnets having high magnetic properties as aimed at
in the present invention.
According to the present invention, the desired
magnetic properties can be obtained, if the Fe-Co-B-R crystals
lS are of the substantially tetragonal system. In most of the
Fe-Co-B-R base compounds, the angles between the axes a, b and
c are 90~ within the limits of measurement error, and aO = bo
cO. Thus, these compounds can be referred to as the
tetragonal system crystals. The term "substantially
tetragonal" encompasses ones that have a slightly deflected
angle between a, b and c axes, e.g., within about 1 , or ones
-
that have ~O slightly different from ~O , e.g., within about 1
% .
To obtain the useful magnetic properties in the present
invention, the magnetic materials and permanent magnets of the
present invention are required to contain as the major phase
an intermetallic compound of the substantially tetragonal
1315571
system crystal structure. By the term "major phase", it is
intended to indicate a phase amounting to 50 vol % or more of
the crystal structure, among phases constituting the crystal
structure.
s The Fe-Co-B-R base permanent magnets having various
compositions and prepared by the manner as hereinbelow set
forth as well as other various manners were examined with an
X-ray diffractometer, X-ray microanalyser (XMA) and optical
microscopy.
EXPERIMENTAL PROCEDURES
(1) Starting Materials (Purity is given by weight %)
Fe : electrolytic iron 99.9 %
B : ferroboron, or B having a purity of 99 %
R : 99.7 % or higher with impurities being mainly
other rare earth elements
Co : electrolytic cobalt having purity of 99.9 %
(2) The experimental procedures are shown in Fig. 15.
The experimental results obtained are illustrated as
below:
(1) Fig. 14 illustrates a typical X-ray diffraction
pattern of the Fe-Co-B-Nd (Fe-lOCo-8B-15Nd in at %) sintered
body showing high properties as measured with a powder X-ray
diffractometer. This pattern is very complicated, and can not
~5 be explained by any R-Fe, Fe-B or R-~ type compounds developed
yet in the art.
(2) XMA measurement of the sintered body of (1)
1315571
- 52 -
h~reinabove under test has indicated that it comprises three
or four phases. The major phase simultaneously contains Fe,
Co, B and R, the second phase is a R-concentrated phase having
a R content of 70 weight % or higher, and the third phase is
an Fe-concentrated phase having an Fe content of 80 weight
or higher. The fourth phase is a phase of oxides.
(3) As a result of analysis of the pattern given in
Fig. 14, the sharp peaks included in this pattern may all be
explained as the tetragonal crystals of QO=8.80A and cO
lo =12.23A~.
In Fig. 14, indices are given at the respective X-ray
peaks. The major phase simultaneously containing Fe, Co, B
and R, as confirmed in the XMA measurement, ha~ turned out to
exhibit such a structure. This structure is characterized by
its extremely large lattice constants. No tetragonal system
compounds having such large lattice constants are found in any
one of the binary system compounds such as R-Fe, Fe-B and B-R.
(4) Fe-Co-~-R base permanent magnets having various
compositions and prepared by the aforesaid manner as well as
other various manners were examined with an X-ray
diffractometer, XMA and optical microscopy. As a result, the
following matters have turned out:
(i) Where a tetragonal system compound having macro
unit cells occurs, which contains as the essential components
R, Fer Co and B and has lattice constants ~o of about 9 A and
cO of about 12 A, good properties suitable for permanent
magnets are obtained. Table 6 shows the lattice constants of
~ 53 ~ 1 31 5571
tetragonal system compounds which constitute the major phase
of typical Fe-Co-B-R type magnets, i.e., occupy 50 vol % or
mole of the crystal structure.
In the compounds based on the conventional binary
system compounds such as R-Fe, Fe-B and B-R, it is thought
that no tetragonal system compounds having such macro unit
cells as mentioned above occur. It is thus presumed that no
good permanent magnet properties are achieved by those known
compounds.
_ 54 - ~ 3 1 5 57 ~
Table 6
crystal structure of various Fe-B-R/Fe-Co-B-R type compounds
_ structure lattice constants
of major phase of maior phase
No. alloy compositions (system) ~o tA) cO tA)
1 Fe-15Pr-8B tetragonal 8.84 12.30
2 Fe-lSNd-8B , 8.80 12.23
3 Fe-15Nd-8B-lNb ll 8.82 12.25
4 Fe-15Nd-8B-lTi .. 8.80 12.24
Fe-lOCo-15Nd-8B n 8.79 12.21
6 Fe-20Co-15Nd-BB " 8.78 12.20
7 Fe-2OCo-15Nd-8B-lV n 8.83 12.24
8 Fe-20Co-15Nd-8B-lSi ll 8.81 12.19
9 Fe-6Nd-6B body~æ~tered cubic 2.87
10 Fe-15Nd-2B rhombohedral 8.60* 12.50*
N.B.: (*) indicated as hexagonal
-
.
1315~7~ i
(ii) Where said tetragonal system compound has a
suitable crystal grain size and, besides, nonmagnetic phases
occur which contain much R, good maqnetic properties suitable
for permanent magnets are obtained.
With the permanent magnet materials, the fine particles
having a high anisotropy constant are ideally separated
individually from one another by nonmagnetic phases, since a
high Hc is then obtained. To this end, the presence of 1 vol
% or higher of nonmagnetic phases contributes to the high Hc.
In order that Hc is no less than 1 kOe, the nonmagnetic phases
should be present in a volume ratio between 1 and 45 vol %,
preferably between 2 and 10 vol ~. The presence of 45 % or
hîgher of the nonmagnetic phases is unpreferable. The
nonmagnetic phases are mainly comprised ~of intermetallic
compound phases containing much of R, while oxide phases serve
partly ef~ectively.
(iii) The aforesaid Fe-Co-B-R type tetragonal system
compounds occur in a wide compositional range.
Alloys containing, in addition to the Fe-Co-B-R base
components, one or more additional elements M and/or
impurities entrained in the process of production can also
exhibit good permanent magnet properties, as long as the major
phases are comprised of tetragonal system compounds.
As apparent from Table 6 the compounds added with M
based on the Fe-B-R system exhibit the tetragonal system as
well as the Fe-Co-B-R-M system compounds also does the same.
- 56 - 1 31 5571
Detailed disclosure regarding other additional elements M
as disclosed in the Canadian Patent application No. 431,730
filed on July 4, 1983.
The aforesaid fundamental tetragonal system compounds
are stable and provide good permanent magnets, even when
they contain up to 1 % of H, Li, ~a, K, Be, Sr, Ba, Ag,
zn, N, F, Se, Te, Pb, or the like.
As mentioned above, the Fe-Co-B-R type tetragonal
system compounds are new ones which have been entirely
unknown in the art. It is thus new fact that high
properties suitable for permanent magnets are obtained by
forming the major phases with these new compounds.
In ~he field of R-Fe alloys, it has been reported to
prepare ribbon magnets by melt-quenching. However, the
invented magnets are different from the ribbon magnets in
the following several points. That is to say, the ribbon
magnets can exhibit permanent magnet properties in a
transition stage from the amorphous or metastable crystal
phase to the stable crystal state. Reportedly, the ribbon
magnets can exhibit high coercive force only if the
amorphous state still remains, or otherwise metastable
Fe3B and R6Fe23 are present as the major phases. The
invented magnets have no sign of any alloy phase remaining
in the amorphous state, and the major phases thereof are
not Fe3B and R6Fe23.
The present invention will now be further explained
with reference to the following example.
- 57 -
1315571
EXAMPLE
An alloy of 10 at ~ Co, 8 at % B, 15 at ~ Nd and the
balance ~e was pulverized to prepare powders having an average
particle size of 1.1 ~m. The powders were compacted under a
pressure of 2 t/cm2 and in a magnetic field of 12 kOe, and
the resultant compact was sintered at 1080C for 1 hour in
argon of 1.5 Torr.
X-ray diffraction has indicated that the major phase of
the sintered body is a tetragonal system compound with lattice
constants ao=8.79A and c~=12.21A~ As a consequence of XMA and
optical microscopy, it has been found that the major phase
contains simultaneously Fe, Co, B and Pr, which amount to 90
volume % thereof. Nonmagnetic compound phases having a R
content of no less than 80 % assumed 4.5 % in the overall with
lS the remainder being substantially oxides and pores. The mean
crystal grain siæe was 3.1 ~m.
The magnetic properties measured are : Br = 12.~ kG,
iHc = 9.2 kOe, and (BH)max = 34MGOe, and are by far higher
than those of the conventional amorphous ribbon magnet.
By measurement, the typical sample of the present
invention has also been found to have high mechanical
strengths such as bending strength of 25 kg/mm2, compression
strength of 75 kg/mm2 and tensile strength of 8 kg/mm2.
This sample could effectively be machined, since chipping
hardly took place in machining testing.
As is understood from the foregoing, the present
invention makes it possible to prepare magnetic materials and
- 58 - 1315571
sintered anisotropic permanent magnets having high remanence,
high coercive force and high energy product with the use of
less expensive alloys containing light-rare earth elements, a
relatively small amount of Co and based on Fe, and thus
present a technical breakthrough.
