Note: Descriptions are shown in the official language in which they were submitted.
RD-11,433
1~ ~51~2
Th~ present invention relates generally to the
metal alloy art and is more particularly concerned with
novel amorphous metal alloys having a unique combination of
magnetic and physical properties, and is further concerned
with ribbons and other useful articles made therefrom.
While it has been recognized by those skilled
in the art that amorphous metals with high saturation
magnetization might be used to advantage in electrical
apparatus such as distribution and power transformers, such
alloys are lacking in necessary ductility and stability for
this purpose. Thus, the iron-rich alloy Fe80B20 has a
4 ~ Ms of approximately 16,000 Gauss but begins to
crystallize within two hours at about 325C and is quite
difficult to produce in ductile ribbon form for electrical
machinery apparatus. Other amorphous alloys known heretofore
have somewhat greater stability and adequate ductility for
this purpose, but their saturation magnetization is too low.
This invention is based upon the discovery that a
very narrow range of iron, boron and silicon amorphous
alloys have both the desired magnetization and other pro-
perties for superior performance in electrical apparatus
such as motors and transformers. Consequently it is now
possible by means of this invention to provide an amorphous
metal in the form of a ribbon sufficiently ductile to be
readily used in electrical apparatus construction which has
good magnetic properties and elevated temperature stability.
FIGURE 1 is a ternary diagram plotting saturation
~ magnetization fo~ a variety o$ iron, boron and silicon alloys
at room temperature (30C~.
FIGURE 2 i5 a ternary diagram plotting coercivity
for a variety o$ iron, boron and silicon alloys;
FIGURE 3 is a ternary diagram plotting the
~`
- - . :: . :
~14S~2 RD-11,433
crystallizatlon temperature for said alloys and
FIGURE 4 is a composite of the saturation
magnetization contour lines of FIGURE 1 and the coercivity
contour lines of FIGURE 2 with the 320C contour line from
Figure 3 superimposed thereon. Shaded region A, B, C, D, E,
F, A designates those iron-boron-silicon ternary amorphous
metal alloy compositions simultaneously exhibiting the
properties of saturation magnetization of at least about
174 emu/g at about 30C, intrinsic coercivity after
annealing of less than about 0.03 oersteds and
crystallization temperature of at least about 320 C.
Referring now to the drawings and particularly FIGURE
1 it can be seen that a superior group of alloys is formed
from all alloys of iron, boron and silicon ~ithin the
broken lines, i.e., of from 80 atom percent iron, 19 atom
percent boron and 1 atom percent silicon to 81 3/4 atom
percent iron, 17 1/4 atom percent boron and 1 atom percent
silicon to 81 3/4 atom percent iron, 12 1/4 atom percent
boron and 6 atom percent silicon to 82 1/4 atom percent
iron, 11 3/4 atom percent boron and 6 atom percent silicon.
However, this designation includes only part of the spectrum
of iron-boron-silicon amorphous metal alloys exhibitin~
the unique confluence of properties comprising this
invention. This complete ~pectrum is described hereinafter
in connection with FIGuRE 4.
In FIGURE 1 saturation magnetizations are plotted
for a variety of amorphous alloys. Magnetizations at room
temperature and below Were determined on small weighed
specimens in a vibrating sample magnetometer to a maximum
field of 20 KOe. Results were extxapolated to H - oo using
a l/H function. ~alues above room temperature were
obtained from the reIative magnetization curves normalized
~ ~ ~ 5 ~ z RD-11,433
to the value of magnetization at room temperature. From
an examination of the diagram it can be seen that the
alloys of the invention have a desirable saturation
magnetization of 178 emu/g at room temperature (30C~.
In FIGURE 2 the intrinsic coercivity is plotted
for a number of iron-boron-silicon alloys which was
determined on 10 cm. long ribbons set into a 20 cm. long
solenoid which was then annealed for 120 min. at a few
degrees centrigrade below the crystallization temperatures
shown in FIGURE 3. A small sense coil was connected to an
integrating flux meter and the magnetization vs filed was
then displayed on an X-Y recorder as the field was slowly
varied. From an examination of the diagram it can be seen
that the lowest coercivity of 0.02 Oe is found with the
alloys having the desirable high saturation magnetization
of 178 emu/g reported in FIGURE 1.
In FIGURE 3 crystallization temperatures are
reported as determined by noting the temperature at which
the coercivity starts to increase after 2 hour exposures
at increasing temperature. From an examination of the
diagrams it can be seen that the alloys found to have high
saturation magnetization and low coercivity are also found to
have acceptably high crystallization temperatures.
Crystallization temperatures up to 340 C are obtained for
the 6 atom percent silicon alloys compared to 310-315 C
for the Fe82B18 alloy. This is desirable as it permits
the allo~ to be annealed to relieve the stresses and reduce
the initial high coercive field without permitting the
amorphous alloy to crystallize and lose its desirable
magnetic ~ualities. Thus ~ith the alloys of the invention
it is possible to anneal frQm above about 320 C ~ithout
cr~stallization occurring. Figure 4 presents a composite
~1~5~ RD-11,433
of the gradient lines of FIGURES 1 and 2 with the 320 C
contour line of FIGURE 3 added thereto. It is this
unification of data, which focuses on the discovery wherehy
for the first time those amorphous alloys of the iron-boron-
silicon system have been identified in which there is a
confluence of the properties of high room temperature
saturation magnetization, high crystallization temperature
and low coercivity. As can be seen from FIGURE 1, there is
a sharp increase in the steepness of the gradient of the
saturation magnetization contour lines from the value of 174
emu/g to higher ~alues. It was never previously recognized
that amorphous alloys in this system could be found with
the unusual combination of properties of saturation
magnetization at room temperature (i.e. about 30 C) of at
least about 174 emu/g, intrinsic coercivity of less than
about 0.03 oersteds and crystallization temperature of at
least about 320C. Alloys exhibiting this unusual collection
of properties are found in the shaded area bounded by the
gradient lines of coercivity, saturation magnetization and
crystallization temperature whose intersections are labeled
~, B, C, D, E, F. Even more effective alloy COmpQsitiOnS
are located in the area designated a, b, c, d defined by the
compositions 81 atom percent iron, 16 atom pecent boron and
3 atom percent silicon (point a); 81 3/4 atom percent iron,
15 1/4 atom percent boron and 3 atom percent silicon
(point d~; 81 1/2 atom percent iron, 13 1/2 atom percent
horon and 5 atom percent silicon (point b~, and 82 atom
pexcent iron, l3 atom percent boron and S atom percent
81.3 15.7Si3 and Fegl 7B13-3Si5 as well as the
aptimum composition, which has an iron content of 81 1/2
atom percent, a horQn cantent of 14 1/2 atQm percent and a
silicon content o~ 4 atom percent are part of area a,b,c,d. --
~ S~6Z RD-11,433
In practicing this invention, novel alloys
defined above and claimed herein are prepared suitable by
mixing together the alloy constituents in the required
proportions in the form of powders and then melting the
mixture to provide molten alloy for casting to ribbon of
the desired dimensions. The casting is preferably carried
out through the use of the method disclosed and claimed in
Canadian application Serial No. 321,822, filed Fèbruary 16,
1979, in the name of John L. Walter and assigned to the
lQ assi~nee hereof. The apparatus described in that application
as implementing the therein-claimed method may likewise be
used to provide long lengths of ribbons of this invention
of uniform ~idth and thickness and smooth edges and surfaces.
Cooling is carried out in the casting operation at a rate
sufficient to produce amorphous material.
While variations in melting point temperatures
between alloys of this invention may impose requirements which
vary with respect to alloy melting and casting operations, the
prepaXation and processing of these alloys can be carried
out with uniformly satisfactory results by following the
above procedure and using the described equipment. In other
~ords, the results of this invention are reproducible in a
substantially routine manner so long as the compositional
limitations stated above and in the appended claims are
strictly observed in the preparation of the alloys.
Ribbons of amorphous alloys claimed herein and
havin~ the properties detailed in FIGURES 1, 2 and 3 are made
by directing a stream of the alloy onto the surface of a
rapi:dl~ revolYing chill roll or dxum as described in EXAMPLE 1
of Canadian p~tent application ~erial No.321,822, noted above.
A t~pical ribbon has a thickness of O.Q025 cm and is 0.13 cm.
wide. The amorphous nature of the xesulting ribbon is-
~ 5~2 RD-11,433
confirmed by X-ray diffraction, differential scanning
calorimetry, and by magnetic and physical property
measurements. When the segments are annealed in purified
nitrogen for two hours at temperatures ranging from 100C
to 400C the crystallization temperature is taken as that
temperature, for the 2-hr. anneal, at which the coercive force
abruptly increases.
To prepare a transformer or motor stator, strips
of the aforesaid alloy about 1/2" wide and 2 mils thick can
be coated with a binder such as polyamide-imide and the
strips placed 6 layers deep in a non-magnetic die cavity of
stainless steel lined with Teflon-coated a-luminum with
alternating layers at 90. The strips are held in place by
means of permanent magnets placed under the die and the
composite pressed at 2000 psi and 330C for 2 minutes after
allowing the die to preheat to 330C for a few minutes
without pressure to equilibrate and drive out excessive air
and water from the die and ribbon. The composite is then
annealed at 325C for 2 hours and found to have a low coercive
force and high saturation magnetization.
Other composites are formed with or without a
binder with similar results. Other suitable binders include
the epoxies, polyamide-imides, cyanoacrylates, and phenolics.
The binder should have a coefficient of thermal expansion
compatible with the metal ribbon, be electrically insulating,
cure rapidly and be able to meet the thermal requirements
of the intended application and annealing if required. In some
applications there are further re~uirements such as being
compatible with commercial refrigements when used for air
conditioning compressor motors.
The above method for preparing a stator is
described and claimed in United States patent 4,201,837
- 6 -
11~51~2 RD-ll,433
issued May 6, 1980 to J.H. Lupinski and assigned to the present
assignee.
To prepare a wound-type transformer the amorphous
metal foil, with widths, for example, up to 6 inches wide,
may be wound on a mandrel with a circular or rectangular
cross-section. The number of turns wound onto the mandrel,
and the width of the tape, will depend on the transformer
rating.
It will be understood by those skilled in the art
that slight but obvious modifications can be made which will
fall within the scope of the invention. For example, an
article of manufacture claimed herein may contain a minor
amount of crystalline material which will not seriously
impair its desirable properties. Accordingly, depending upon
the particular article of manufacture and its intended use,
the article may contain up to 10% of crystalline material.
Consequently the application is intended to be limited only
by the appended claims.
- 7 -
