Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTION
AMORPHO~S METAL ALLOYS HAVING
_
ENHANCED AC MAGNETIC PROPERTIES
BACK5ROUND OF TEI~ INVENTIO~
Field of the Invention
-
The invention relates to amorphous metal alloy
compositions an~, in particular, to amorphous alloys
containing iron, silicon and boron having enhanced A.C.
magnetic properties.
Description of the Prior Art
Investigations have demonstrated that it is
possible to obtain solid amorphous materials from
certain metal alloy compositions. An amorphous material
substantially lacks any long range atomic order and is
characterized by an X-ray diffraction profile consisting
o~ broad intensity maxima. Such a profile is qualita-
tively similar to the diffraction profile of a liquid or
ordinary window glass. This is in contrast to a
crystalline material which produces a diffraction pro-
file consisting of sharp, narrow intensity maxima.
These amorphous materials exist in a
metastable state. Upon heating to a sufficiently high
temperature, they crystallize with evolution of the heat
of crystallization, and the X-ray diffraction profile
changes from one having amorphous characteristics to one
having crystalline characteristics.
Novel amorphous metal alloys have been
disclosed by H.S. Chen and D.E. Polk in U.S. Pat. No.
3,~56,513, issued Dec. 24, 1974. These amorphous alloys
have the formula MaYbZC where M is at least one metal
~52~3
--2--
selected from the group of iron, nickel, cobalt,
chromium and vanadium, Y is at least one element
selected from the group consistin~J of phosphorus, boron
and carbon, 2 is at least one element selected from the
group consisting of aluminum, antimony, beryllium,
germanium, indium, tin and silicon, "a" ranges frorn
about 60 to ~0 atom percent, "b" ranges froM about 10 to
30 atom percent and i'c" ranges from about 0.1 to 15 atom
percent. These amorphous alloys have been found suit-
able for a wide variety of applications in the forrn ofribbon, sheet, wire, powder, etc. The Chen and Polk
patent also discloses amorphous alloys having the
fon-nula TiXj, where T is at least one transition metal,
X is at least one element selected from the group con-
sisting of aluminum, antimony, beryllium, boron,germanium, carbon, indium, phosphorus, silicon and tin,
"i" ranges from about 70 to 87 atom percent and "j"
ranges from about 13 to 30 atom percent. These
amorphous alloys have been found suitable for wire
applications.
~ t the time that the amorphous alloys
described above were discovered, they evidenced magnetic
properties that were superior to then known poly-
crystalline alloys. Nevertheless, new applications
requiring improved magnetic properties and higher
thermal stability have necessitated efforts to develop
additional alloy compositions.
SUMMARY OF THE INVENTION
.
In accordance with the present invention,
there is provided a metal alloy which is at least 90%
amorphous consisting essentially of a composition having
h f 1 Fe Si ~ wherein "a" "b" and "c" are atomic
percentayes ranging from about 75 to 7~.5, 4 to 10.5 and
11 to 21 respectively, with the proviso that the sum of
"a", "b" and "c" equals 100.
The subject alloys are at least 90% amorphous
and preferably at least 97% amorphous, and most prefer-
ably 100~ amorphous, as determined by X-ray diffraction.
5;3
The alloys are fabricated by a known process which com~
prises forming a melt of the desired composition and
quenching at a rate OL at least about 105C/ sec. by
casting molten alloy onto a rapidly rotatiny chill wheel.
In addition, the invention provides a method
of enhancing the magnetic properties of a metal alloy
which is at least ~0~ amorphous consisting essentially
of a composition having the formula FeaSibBc wherein
"a", "b" and "c" are atomic percentages ranging from
about 75 to 7~.5, 4 to 10.5 and 11 to 21, respectively,
with the proviso that the sum of "a", "b" and "c" equals
100, which method comprises the step of annealing the
amorphous metal alloy.
Further, the invention provides a core for use
in an electromagnetic device; such core comprising a
metal alloy which is at least 90% amorphous consisting
essentially of a composltion having the formula Fe SibB
wherein "a", "b" and "c" are atornic percentages ranging
frorn about 75 to 78.5, 4 to 10.5 and 11 to 21, respec-
tively, with the proviso that the sum of "a", "b" and"c" equals 100.
The alloys of this invention exhibit improved
A.C. magnetic properties at temperatures up to about
150C. As a result, the alloys are particularly suited
for use in power tranformers, aircraft transforrners,
current transformers, high frequency transformers (e.g.
transformers having operating frequencies ranging from
about 400 13z to 100 kHæ~, switch cores, high gain
magnetic ~nplifiers and low frequency inverters.
DETAILED DESCRIPTION OF T~E INVENTION
_
The composition of the new amorphous Fe-Si-B
alloy, in accordance with the invention, consists of 75
to 7~.5 atom percent iron, 4 to 10.5 atom percent
silicon and 11 to 21 atom percent boron. Such com-
positions exhibit enhanced A.C. magnetic properties.The improved magnetic properties are evidenced by high
magnetization, low core loss and low volt-ampere demand
which remain constant and stable at temperatures up to
125C. A preferred composition within the foregoing
2~.~
ranges consists of 78 atom Percent iron, 6 to 10 atom
percent silicon, the balance being boron.
The alloys of the present invention are at
least about 90~ amorphous and preferably at least about
97~ amorphous and most preferably 100% amorphous.
Magnetic properties are improved in alloys possessing a
greater volume percent of amorphous material. The
volume percent of amorphous material is conveniently
determined by X-ray diffraction.
The amorphous metal alloys are formed by cool-
ing a melt at a rate of abou-t 105~ to 106C/sec. The
purity of all materials is that found in normal com-
mercial practice. A variety of techniques are available
for fabricating splat-auenched foils and rapid-quenched
continuous ribbons, wire, sheet, etc. Typically, a
particular composition is selected, powders or granules
of the re~uisite elements (or of materials that decom-
pose to form the elements, such as ferroboron, ferro-
silicon, etc.) in the desired proportions are melted and
homogenized, and the molten alloy is rapidly quenched on
a chill surface, such as a rotating cylinder.
The most preferred process for fabricating
continuous metal strip containing the alloys of the
invention is that set forth in U.S.P. 4,142,571 to
Narasimhan. The Narasimhan patent sets forth a method
of forming a continuous metal strip by depositing molten
metal onto the surface of a moving chill bod~. The
method comprises the steps of (a) moving the surface of
a chill body in a longitudinal direction at a constant
predetermined velocity of from about 100 to about 2000
meters per minute past the orifice of a slotted nozzle
defined by a pair of generally parallel lips located
proximate to the surface such that the gap between the
lips and the surface is from about 0.03 to about 1
millimeter, the orifice being arranged generally
perpendicular to the direction of movement of the
chill body, and (b) forcing a stream of molten
metal through the orifice of the nozzle into con-
~5~53
tact with ~the s~rface of the moving chill body to permitthe metal to solidify thereon to form a continuous strip
Preferably, the nozzle slot has a width of from about
0~34 to 1 millimeter, the first lip has a width at least
equal to the width of the slot and the second lip has a
width of from about 1.5 to 3 times the width of the slot
amorphous metal strip produced in accordance with the
~arasimhan process has a width of at least about 7 mill~
imeters, preferably at least about 1 centimeter and,
more preferably yet, a width of at least about 3 centi-
meters. The strip is at least 0.02 millimeter thick but
may be as thick as about 0.14 millimeter, or thicker,
depending on the melting point, solidirication and
crystallization characteristics of the alloy employed.
The alloys of the present invention have an
improved processability as compared to other iron-based
metallic glasses, since the subject alloys demonstrate a
minimized melting point and maximized undercooling.
The magnetic properties of the subject alloys
can be enhanced by annealing the alloys. The method of
annealing generally comprises heating the alloy to a
temperature sufficient to achieve stress relief but less
than that required to initiate crystallization, cooling
the alloy, and applying a magnetic field to the alloy
during the heating and cooling. Generally, a temper-
ature ranye of about 340C to 440C is employed during
heating. A rate of cooling range of about 0.5C/min. to
75C/min. is employed, with a rate of about 1C/min. to
16C/min. being preferred.
As discussed above, the alloys of the present
invention exhibit improved magnetic properties that are
stable at temperatures up to about 150C, rather than a
maximum of 125C as evidenced by prior art alloys. The
increased temperature stability of the present alloys
allows utilization thereof in high temperature applica-
tions, such as cores in transformers for distributing
electrical power to residential and commercial con
sumers.
5~
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When cores comprising the subject alloys are
utilized in electrornagnetic devices, such as trans-
formers, they evidence high magnetization, low core loss
and low volt-ampere demand, thus resulting in more
efficient operation of the electromagnetic device. The
loss of energy in a magnetic core as the result of eddy
currents, which circulate through the core, results in
the dissi~pation of energy in the form of heat. Cores
made from the subject alloys require less electrical
energy for operation and produce less heat. In appli-
cations where cooling apparatus is required to cool the
~ransformer cores, such as transformers in aircraft and
large power transformers, an additional savings is
realized since less cooling apparatus is required to
remove the smaller arnount of heat generated by cores
made from the subject alloys. In addition, the high
magnetization and high efficiency of cores made from the
subject alloys result in cores of reduced weight for a
given capacity rating.
The following examples are presented to
provide a more complete understanding of the invention.
The specific techniques, conditions, materials, propor-
tions and reported data set forth to illustrate the
principles and practice of the invention are exemplary
and should not be construed as limiting the scope of the
invention.
EXAMPLES
Toroidal test samples were prepared by winding
approximately 0.030 kg of 0.0254 m wide alloy ribbon of
various compositions containing iron, silicon and boron
on a steatite core having inside and outside diameters
of 0~0397 m and 0.0445 m, respectively. One hundred and
fifty turns of high temperature magnetic wire were wound
on the toroid to provide a D.C. circumferential field of
795.8 ampere/meter for annealing purposes. The samples
were anuealed in an inert gas atmosphere for 2 hours at
a temperature ranging from 340C to 440C with the 795.8
A/m field applied during heating and cooling to
5~S3
--7--
determine the optimum field annealing conditions for
each composition. The optimum field annealing condition
for each composition is that at which the exciting power
of the core is lowest. The samples were cooled at a
rate of approximately 10C/min.
The A.C. magnetic properties, i.e., power loss
(watts/kilogram) and exciting power (RM~ Volt-amperes/
kilogram), of the samples were measured at a frequency
of 60 Hz and a magnetic intensity of 1.4 Tesla by the
sine-flux method.
Field annealed A.C~ magnetic values for a
variety of alloy compositions that are within the scope
of the present invention are shown in Table I.
Table I
FIELD ANNEALED A.C. MAGNETIC MEASUREMENTS FOR
A~IORPHOUS METAL ALLOYS ~ITHIN THE SCOPE OF THE INVENTION
Composition A.C. Properties: 60Hz, 1.4T
Fe B Si Room Temperature 100C
(atorn %) Power Exciting Power Exciting
Loss Power Loss Power
Ex. (weight %) (W/kg) (VA/kg) (W/kg) (VA/kg)
1. 7515 100.25 1.81 0.23 2.34
94.4 3.5 6.1
2. 7614 100.20 0.67 0.20 0.92
90.8 3.2 6.0
3. 7713 100.21 1.31 0.18 2.06
91.0 3.0 6.0
4. 7812 10.27 .39 .30 .37
91.4 2.7 5.9
5~ 7818 4.21 .47 .22 .95
93.4 4.2 2.4
6. 7817 50.18 0.24 0.20 0.27
93.1 3.~ 3.0
7. 7816 60.33 0.41 0.37 0.67
92.7 3.7 3.6
8. 7814 ~.23 .34 .28 .42
92.1 3.2 4~7
9. 7812 10.27 .39 .23 .24
91.4 2.7 5.9
For comparison, the compositions of some amor-
phous metal alloys lying outside the scope of the inven-
~LSZ5~
--8--tion and their field annealed A.C. measurements are
listed in Table II~ These alloys, in contrast to those
within the scope of the present invention, h~ve higher
core loss and higher volt-ampere demand at roorn
temperature and at 100C.
Table II
FIELI) ANNEALED A.C. MAGI~ETIC MEASUREMENTS FOR AMORPHOUS
METAL ALLOYS NOT WITHIN THE SCOPE OF THE INVENTION
Composition A.C. Properties: 60~1z, 1.4T
Fe B Si Room Temperature 100C
l0(atom %) Power Exciting Power Exciting
Loss Power Loss Power
Ex.(weight %) (W/kg) (VA/kg) _(W/kg) (VA/kg)
l0. 80 l0 lO>.2* >.2* _ ** _ **
92.0 2.2 5.8
ll. 81 l0 9_ ** _ ** _ ** _ **
92.6 2.2 5.2
12. 82 9 9_ ** _ ** _ ** _ **
92.9 2 5.1
13. 78 10 12.27 2.08 .19 2.58
90.7 2.3 7
14. 78 8 14_*** _*** _*** _***
90.l 1.8 8.1
* Values indicated are at 1.26T and are expected to be
higher at 1.4T.
** VA/kg at 1.4T >l0; Power Loss corresponding to such
high VA demand is innacurate.
*** Not castable into ductile ri~bon.
