Note: Descriptions are shown in the official language in which they were submitted.
MA _ETIC DEVICE5
Background of the Invention
I. Field of the Invention
The invention is concerned with magnetic devices, and
more particularly, with magnetic devices utilizing amorphous
metal alloys as cores.
2. Description of the_Prior Art
Magnetic devices, such as transformers, motors, genera-
tors and the like, include cores which are composed of magnetically
soft material.
Outstanding characteristics required of magnetically
soft materials are: (a) low hysteresis 105s resulting from inter-
nal friction during a magnetic cycle; (b) low eddy current loss
from electric currents induced by changes in flux; (c) low coer-
cive force; (d~ high magnetic permeability and, in some cases,
constant permeability at low field strengths; (e) high saturation
value; and (f~ minimum or definite change in permeability with
temperature in special applications. Cost, availability and
ease of processin~ are other factors that influence the final
choice of material.
Investigations have revealed a number of metal alloys
suitable for use as cores in magnetic devices. These include high
purity iron, silicon steels, iron-nicke] alloys, iron-cobalt alloys,
and ferrites. Nevertheless, new compositions are continually
sought in which the foregoing properties are improved.
Summary of the Invention
In accordance with the invention, magnetic devices
utilize amorphous magnetic metal alloys as cores. The metal alloys
are at least 50% amorphous, as determined by X-ray diffraction,
and preferably at least 80% amorphous, and more preferably, at
least 95% amorphous. The metal alloys have the formula
~k
~ FE)7o-gsTo-lsxl5-25~
where FE is at least one of the elements of iron, cobalt and nickel,
T is at least one of the transition metal elements and X is at
least one of the metalloid elements of aluminum, antimony~ beryl-
lium, boron, germanium, carbon, indium, phosphorus, silicon and
tin. Preferably, X is at least one of the elements of phosphorus,
boron, carbon, silicon and aluminum. Used as cores of magnetic
devices, these amorphous metal alloys evidence generally superior
properties, as compared with well-known polycrystalline metal
alloys utilized in the prior artO
Detailed Description of the Invention
A theory has not yet been developed to correlate many
macroscopic physical properties of polycrystalline metal alloys
and of amorphous metal alloys having substantially the same com-
position. Many of the physical properties of previously disclosed
amorphous metal alloys tend to change at elevated temperatures.
In contrast to this, however, a class of amorphous metal alloys,
whose compositions are given below, exhibit the very low coercive
force, high permeability, high electrical resistivity and other
desirable properties required for use in magnetic devices.
~ morphous metal alloys used in the invention may he
represented by the following formula (the subscripts are in atom
percent):
(FE)70-8~o-lsxl5-25
where FE is at least one iron group element, T is at least one
transition metal element and X is at least one of the metalloid
elements of aluminum, antimony, beryllium, boron, germanium,
carbon, indium, phosphorus, silicon and tin. Iron group elements
.
are iron, cobalt and nickel. As used herein, the term "transi-
tion metal elements" i8 intended to include those elements listed
in Groups IB to VIIB and VIII of the Periodic Table. Preferably,
X is at least one of the elements of phosphorus,
--2--
'~,,.
~2a~
boron and carbon, with minor additions (up to about 5 atom percent)
of aluminum and silicon. Typical compositions include Feg0pl6Bl~
A13, Fe40Ni40Pl~B6, Fe2gNi4gPl~B6Si2~ Fe2sNi25co2ocrloB2o~ Fe55Ni8-
Co5Crl5B17~ Fe82.6Pl6AllgO.4~ Fe82.6P16Sil.sB0.4~ and Fe30Ni45-6
Cr5PlgBo.4. The purity of all elements described is that ound
in normal commercial practice.
Preferred compositions depend on the specific application
desired. For high saturation value greater than about 15 kilogauss,
it is desired that a relatively high amount of cobalt and/or iron
be present. Accordingly, such a composition may be represented by
the formula
(co~F~e)7o-8sTo-l5xl5-25
where T and X are defined as above. For low coercive force less
than about 0.05 oersteds, the preferred composition may be
represented by the formula
(Ni,Fe)70-8sTo-lsxl5-25
where T and X are given as above and where the ratio of nickel
to iron ranges from about 5:3 to 1:1.
The amorphous metal alloys are formed by cooling a melt
20 at a rate of about 105 to 106C/sec. These amorphous metal alloys
are usually at least 50% amorphous when processed in this manner,
as determined by X-ray diffraction and may be utilized in some
applications. It is preferred, however, that the amorphous alloys
be at least 80% amorphous, and more preferably, at least 95% amor-
phous to realize maximal performance in magnetic devices.
A variety of well-known techniques are available for
fabricating splat-quenched foils and rapid-quenched continuous
ribbon, wire, sheet, etc. Typically, when used in cores for
magnetic device applications, these alloys conveniently take the
form of wire or ribbon. The wire and ribbon are convenien-tly
prepared by casting molten material directly onto a chill surface
or into a quenching medium of some sort. Such processing tech-
niques considerably reduce the cost of fabrication, since no
intermediate wire-drawing or ribbon-forming procedures are
required.
These amorphous metal alloys evidence high tensile
strength, typically about 200,000 to 600,000 psi, depending on
the particular composition. This is to be compared with poly-
crystalline alloys, which are used in the annealed condition and
which usually range from about 40,000 to 80,000 psi. A high
tensile strength is an important consideration in applications
where high centrifugal forces are present, such as experienced by
cores in motors and generators, since higher strength alloys
allow higher rotational speeds.
All of the amorphous metal alloys evidence a high elec-
trical resistivity, ranging from about 160 to 180 microhm-cm at
25C, depending on the particular composition. Typical prior art
materials have resistivities of about 45 to 160 microhm-cm. A high
resistivity is useful in AC applications for minimizing eddy current
losses, which, in turn, are a factor in reducing core loss.
The fabricability and ductility of the amorphous metal
alloys are good. In the prior art, mechanical treatment, such as
punching and stamping, tends to degrade magnetic properties.
This degradation must be overcome with additional thermal treatment.
In amorphous metal alloys used in accordance with the invention,
the magnetic properties do not change and in fact, slightly improve
in many cases through such treatment.
A further unexpected characteristic of the amorphous
metal alloys is that lower coercive forces are obtained than with
prior art compositions of substantially the same metallic content,
thereby permitting more iron, which is relatively inexpensive, to
be utilized, as compared with a greater proportion of nickel,
which is more expensive.
Depending on the particular application desired, the
amorphous metal alloys are useful as cores for magnetic devices
such as transformers, motors, generators and the like.
Examples
Magnetic measurements were made on several amorphous
metal alloy specimens as indicated below. Ribbons were wound
into multiple layer rings of diameter from about 1 to 2 cm,
similar to tape wound cores for small and miniature transformers.
To measure the magnetic induction of the ring sample, primary
and secondary windin~s of enameled or polytetrafluoroethylene
coated copper wire were applied. Ma~netizing current was provided
by a bipolar operational amplifier controlled manually or driven
by a variable fre~uency signal generator. The output from the
secondary coil was integrated and displayed against field on an
X-Y recorder or on an oscillocope. In this manner, the satura-
tion magnetiz~tion, the remanence, the ratio of remanence to
magnetic induction, the coercive force and the maximum permea-
bility were determined in DC fields.
The results for three samples of amorphous metal alloys
are tabulated in the Table below. Sample 1 had a composition of
FegoP16BlA13 (the subscripts are in atom percent)~ Measurements
were made on ribbon of Sample 1 having dimensions 0.065 inch wide
by 0.0014 inch thick. Sample 2 had a composition Fe40Ni40P14B6.
Measurements were made on ribbon of Sample 2 having dimensions
0.063 inch wide by 0.0013 inch thick. Sample 3 had a composition
Fe2gNi49Pl4B6si2 Measurements were made on D-wire of Sample 3,
which in cross-section is half an ellipse, having dimensions as
follows: the major axis was Q.024 inch and one-half the minor
30 axis was 0.0028 inch.
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For comparison, strips of a polycrystalline alloy having
the composition 50 Ni - 50 Fe had a saturation magnetization of
15.5 kilogauss, a remanence of from 12 to 15 kilogauss, a ratio
of remanence to lnduction of 0.85 ~o 0.95, a coersive force of
0.08 oersteds, and a maximum permeability of 100 x 103. Strips
of another polycrystalline alloy having the composition 80 Ni -
15 Fe - 5 Mo had a saturation magnetization of 8 kilogauss, a
remanence of 4 to 6.5 kilogauss, a ratio of remanence to induction
of 0.5-0.9, a coersive force of 0.03 oersteds, and a maximum
permeability of 200 x 103.
