Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
MANUFACTURE OF POWDER CORES FOR
ELECTROMAGNETIC APPARATUS
BACKGROUND OF THE INVENTION
yield of the Invention
This invention relates to magnetic articles
made as cores and pole pieces and to a process for
making them from metallic glass powder.
Description of the Prior Art
Amorphous metal alloys and articles made
therefrom are disclosed by Chin and Polk in United
States Patent 3,856,513 issued December 24~ 1974. That
patent teaches certain novel metal alloy compositions
which are obtained in the amorphous state and are
superior to previously known crystalline alloys based on
the same metals. The compositions taught therein are
easily quenched to the amorphous state and possess
desirable physical properties. The patent discloses
further that amorphous metal powders having a particle
size ranging from about 10 to 250 em can be made by
grinding or air milling the cast ribbon.
Manufacture of magnetic articles by console-
ration of permalloy and other crystalline alloy powders is known. New applications requiring improved magnetic
properties have necessitated efforts to develop alloys
and consolidation processes that increase, concomitant-
lye r the strength and magnetic response of magnetic
articles.
SUMMARY OF THE INVENTION
_..
The present invention provides amorphous metal
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alloy powders especially suited for consolidation into
bodies having excellent magnetic response. In addition,
the invention provides a method for manufacture of
magnetic articles in which consolidation of glassy metal
powder is effected using a thermomechanical process and
insulating materials.
Articles produced in accordance with the
method of this invention have low Rumanians and
permeabilities which remain constant over a wide
frequency range. Typically, such consolidated magnetic
glassy metal alloy bodies have a relative magnetic
permeability of at least about 15. As used herein, the
term "relative permeability" is intended to mean the
ratio of the magnetic induction in a medium generated by
a certain field to the magnetic induction in vacuum
generated by the same field.
More specifically, molded magnetic metal alloy
articles are produced in accordance with the invention
by a method comprising the step of compacting err-
magnetic glass powder with static pressure at a pressing temperature in the vicinity of the glass transition
temperature and below the crystallization temperature of
said alloy, and at a pressure of about 69 Ma to
690 Ma. consolidated glassy metal alloy body is
thereby formed, which is especially adapted to be post
fabrication annealed at a temperature ranging from about
3~0 to 450C for a time period of about 1 to 4 hours in
the presence of a magnetic yield of about 0 to 800 A/m.
The annealed article has improved impedance permeability
and it particularly suited for use in signal and high
frequency power transformers and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood
and further advantages will become apparent when
reference is made to the following detailed description
of the preferred embodiments of the invention and the
accompanying drawings, in which
Fig 1 is a schematic representation of
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apparatus used to cast amorphous metal powder directly
from the melt, the apparatus having a serrated casting
substrate;
Fig. 2 is a graph showing variation in density
of consolidated objects as a function of pressing time
and temperature;
Fig. 3 is a graph showing variation in
impedance permeability as a function of post fabrication
anneal time;
Fig. 4 is a graph showing variation in
impedance permeability as a function of frequency of
uninsulated and insulated powders;
Fig. 5 is a graph showing variation in
impedance permeability as a function of frequency of
cores made of different particle sizes; and
Fig. 6 is a graph showing the variation in
core loss as a function of post fabrication anneal time.
DETAILED DESCRIPTION OF THE INVENTION
The magnetic compact bodies with permeability
greater than 15 of the present invention are generally
made from glassy metal alloys in powder form The
general process for preparing metallic glass powders
from alloys involves a step of rapid quenching and a
step of atomization. Alloys are cast directly into
ribbon, followed by grinding, ball milling or air
milling into powders or flakes of desirable size range.
To aid the pulverization process, ribbon samples are
subjected to an embrittlement heat treatment below the
crystallization temperature of the alloy.
Alternatively, powders or flakes, defined
herein as particles with the major diameter more than
an order of magnitude smaller than their thickness, can
be cast directly into the final form having a desirable
size range using a serrated casting substrate of the
type illustrated in Figure lo The size of the particles
or flakes thereby produced will vary, depending on the
depth of the serrations and the distance there between.
Typically the serrations comprise a plurality of
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regularly spaced peaks and valleys, the distance between
adjacent peaks ranging from about 0.01 cm to 0.1 cm and
the distance from the top of a peak to the bottom ox a
valley ranging from about 0.005 cm to 0.05 cm Such
configuration of the casting substrate typically yields
powder particles or flakes having a size ranging from
about 0.01 cm to 0.1 cm.
As shown in Figure 1, the apparatus 10 has a
movable chill surface 12~ a reservoir 14 for holding
molten metal 16 and a nozzle 18 in communication at its
top with reservoir I and having at its bottom an open-
in 20 in close proximity to the chill surface 12. The
chill surface 12 has a plurality of regularly spaced
peaks 22 and valleys 24. Adjacent peaks are separated
by a distance, d, of about 0.01 cm to Cot cm. The
distance, y (not shown) from the top ox a peak to the
bottom of a valley is about 0.005 cm to 0.05 cm. Powder
is produced directly by deposition of molten alloy on
the serrated substrate (chill surface 12) which is a
rotatable chill roll, an endless belt (not shown) or the
like, adapted for longitudinal movement at a velocity of
about 100 to 200 meters per minute. The size of the
powder particles thereby produced varies directly with
the magnitude of distances d and y.
In the embodiment shown, the nozzle means has
a slot arranged generally perpendicular to the direction
of movement of the chill surface The slot is defined
by a pair of parallel lips, a first lip and a second lip
numbered in the direction of movement of the chill
surface. The slot of nozzle 18 has a width of from
about 0.2 to about 1 millimeter, measured in the direct
lion of movement of the chill surface. 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 about 3
limes the width of the slot. The gap between the lips
and the chill surface is from about 0.1 to about 1 times
the width of the slot. The preparation of a glassy
alloy can be achieved by following the basic teaching
set forth in US 3,856,553 to Chin, et at. The
resulting sheets, ribbons, tapes and wires are useful
precursors of the materials disclosed here.
Consolidation of the powder is the initial
step in producing a body. Powder adapted for
consolidation can comprise fine powder (having particle
size under 105 micrometers), coarse powder (having
particle size between 105 micrometers and 300
micrometers) and flake (having particle size greater
than 300 micrometers). Consolidation can be obtained by
pressing glassy metal alloy powder near its glass
transition and below the crystallization temperature.
In case low permeabilities (i.e., less than
about 25) are desired, a particle diameter of less than
about 105 micrometers is used. For high permeabilities
(greater than about 100), larger particle diameters of
about 300 micrometers or more are employed
For consolidation, powders can be put in
evacuated cans and then be formed to strips or isostati-
gaily pressed to discs, rings or any other desirable shape such as transformer and inductor cores, motor
stators and rotor parts, and the like. Furthermore,
powders can be warm pressed below the crystallization
temperature and in the region of glass transition
temperature into any desirable shapes of transformer/
inductor cores or motor rotor/stator segments. Console-
ration is believed to result from mechanical interlock
in and short-range diffusion bonding between the
powder or flake particles occurring in the vicinity of
the glass transition temperature. At temperatures too
far below the glass transition temperature Tug the
particles are relatively hard and are not readily
deformed by shear and compressive forces exerted thereon
during consolidation Temperatures too far above Tug
enhance the risk of incipient crystallization of the
amorphous particles during consolidation Generally, it
has been found that interpartical bonding is best
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achieved during consolidation at pressing temperatures
within about 50C of Tug.
The powders can also be mixed with a suitable
organic binder, for instance, paraffin, polysulfone,
polyamide, finlike formaldehyde resins, and then cold
pressed to suitable forms. The amount of binder can be
up to 30 weight percent and is preferably less than 10
weight percent and more preferably between 0~5 and 3
weight percent for high permeability cores. Such wormed
alloy can have a density of at least 60 percent of the
theoretical maximum. The pressed object can be cured at
a relatively low temperature below the curing tempera-
lure of the binder to give more strength and then ground
to final dimensions. The preferred product of this
process comprises shapes suitable as magnetic
components The curing process can be performed with
simultaneous application of a magnetic field.
A metallic glass is an alloy product of fusion
which has been cooled to a rigid condition without cry-
tallization. Such metallic glasses generally have at least some of the following properties: high hardness
and resistance to scratching, great smoothness of a
glassy surface, dimensional and shape stability, motion-
teal stiffness, strength, ductility, high electrical
resistance compared with related metals and alloys
thereof, and a diffuse X-ray diffraction pattern.
me term Allah" is used herein in the convent
tonal sense as denoting a solid mixture of two or more
metals (Condensed Chemical Dictionary Ninth Edition,
Van Nostrand Reinhold Co., New York, 1977). These
alloys additionally contain admixed at least one non-
metallic element. The terms "glassy metal alloy,"
"metallic glass," "amorphous metal alloy" and "vitreous
metal alloy" are all considered equivalent as employed
herein
Lloyd suitable for the processes disclosed in
the present invention include the composition
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phonic 88[Mo,Nb,Ta,Cr,V]O_lO[B,C,S]5 25
Preferred ferromagnetic alloys according to
the present invention are based on one member of the
group consisting of iron, cobalt and nickel. The iron
based alloys have the general composition
I (Cowan 40(Mo~Nb~Ta~v~cr)o-lo 5-25
the cobalt based alloys have the general composition
40_88(Pe,Ni)O_~LO(Mo,Nb,Ta,V,Mn,Cr)O lo(B,C,Si)
and the nickel based alloys have the general composition
Noah Coffey 40(Mo~Nb,Ta,V,Mn,Cr)O_lO(B,C,Si)5_25.
An especially preferred alloy has the
composition 79 atomic percent iron, 16 atomic percent
boron and 5 atomic percent silicon.
Amorphous metallic powders can be compacted to
fabricate parts suitable for a variety of applications
such as electromagnetic cores, pole pieces and the like.
The glassy metal compacts have either high or low
permeability. The resulting cores can be used as
transformer cores, motor stators or rotors and in other
alternating current applications. Amorphous alloys
that are preferred for such applications include
Phoebes' Fe7gB16Si5 and Foe 13.~ 3.5 2
The following examples are presented to pro-
vise a more complete understanding of the invention.
The specific techniques, conditions, materials, proper-
lions 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.
Example 1
Amorphous metallic powders having a particle
size below 300 em and a composition of Phoebes
(subscripts in atom percent) were prepared by air mill-
in ribbon cast directly from the melt according to the
35 procedure detailed in US. patent 4l142,571. Cast
ribbon was also given an embrittlement treatment in an
inert nitrogen atmosphere for 1-2 hours at 400C prior
to ball milling for 16 hours. The above processes
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resulted in fine amorphous particles ranging from 300-
in em. The resulting fine powder particles were sieved
into different size ranges, namely "-325 mesh"
(< 40 em), "-15n mesh" (< 105 em) and "-48 mesh I< 300
em). Powders were then coated with either 1-3 wit% Sue
by mixing the particles with a slurry containing Sue
and methanol or l White Moo using a slurry containing
Moo and methanol. The coated powders of -150 and ~325
mesh size were then pressed in graphite molds at
n temperatures, ranging from 41n-510C for 5, 15 and 30
minutes. The pressure employed was I Ma. Since
the glass transition temperature (To) cannot be
accurately determined for the Pharisee alloy, warm
pressing was conducted over a wide temperature range
A10-51nC below the crystallization temperature
Tx(=53nC). Variation of core density as a function of
pressing conditions is shown in Figure 2. Approximately
8n-85~ of ideal density can be achieved at 460C, l/2
hr. however, pressing time can be shortened at higher
on temperatures to achieve the same density. Also,
various molds can be fabricated to warm press directly
into the desired shape, namely rods, toxoid, HI shapes
etc. necessary for the specific applications.
Example 2
Amorphous metallic powder particles with size
below 105 em of an alloy and a composition of Foibles
were prepared by air milling as indicated in Example l
and also by ball milting after embrittling the as-cast
ribbon by heat treating at ~0C for 1 hr. Air milled
on Powder particles were coated with l wit% Moo. Towardly
cores (ID = 25 mm, OX = 38 mm & thickness = 12 mm) were
fabricated by warm pressing at 430C for 1/2 hr. To
evaluate the effect of a post fabrication anneal,
pressed cores made from both insulated and uninsulated
35 powders were annealed at 435C for 1 to 4 his. and the
corresponding impedance permeability values were deter-
mined and plotted in Figure I
A post fabrication anneal substantially
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improves the permeability and the optimum anneal was
found to be 1-2 his. at 435C for the specific compost-
lion and consolidation process employed in the present
example.
Example 3
Amorphous metallic powder particles with size
below 105 em of an alloy and a composition of Phoebes
were prepared by air milling as indicated in Example 1.
To evaluate the effects of insulation,
towardly cores (I.D. = 25 mm, OLD. = 38 mm and thick-
news - 12 mm) were prepared with 1-3 White Sue or Moo by
warm pressing at 430C for 1/2 hr. Fabricated cores
were then annealed at 435C for 1 hr. and their
impedance permeability was determined as a function of
frequency (1-100 kHz at .1 Tussle induction). The
results are illustrated in Figure 4. The impedance
permeability for the insulated powder cores does not
change with frequency; whereas the permeability for
the uninsulated cores rolls off with frequency due to
eddy current shielding. This constant permeability is
a very important magnetic characteristic desirable for
signal and high frequency power transformer applique-
lions.
Example 4
Amorphous metallic powder particles having
two different size ranges, namely "-48 mesh size"
25 (< 300 em) and "-150 mesh size" (<105 em) were prepared
by air milling in accordance with the procedure set
forth in Example 1. Powder particles were coated with
1 wit Moo pressed to towardly samples (ID = 25 mm,
OX = 38 mm and thickness = 12 mm) and post fabrication
30 annealed at 435C for 1-2 his. Impedance permeability
values of the cores were plotted as a function of
frequency. As shown in Figure 5, higher permeability
was obtained with coarser particle size.
Example 5
Core loss characteristics, in addition to
impedance permeabilities, are important to power
transformer core applications. Towardly cores
IDEA = 25 mm, OX = 38 mm, thickness = 12 mm) were
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prepared from insulated I Moo) powder Of particle size
-48 and -150 mesh using the same alloy Phoebes and
the same fabricator technique described in Example 1.
Fabricated cores were annealed at 435 for 1-3 his. Core
loss values at 50 kHz/.l Tussle are shown in Figure 5.
Optimum heat treatment appears to be greater than 2 his.
at 435C. High frequency core loss values are sub-
staunchly reduced with a smaller particle size and
1-3~ by weight insulation. Powder and insulation
characteristics necessary for optimum low frequency
(60-400 Ho) core loss are substantially different from
those necessary for high frequency applications. Since
eddy currents are not dominant at lower frequencies,
larger particle size (erg. greater than 300 em) with no
insulation is desirable for 60-400 Ho transformer and
motor applications. Also for such lower frequency
transformer and motor applications, post fabrication
annealing should be conducted at lower temperatures, as
in the order of temperatures ranging from about 380 Jo
420C, to avoid partial crystallization, of the
amorphous matrix. For high frequency applications, the
particle size is smaller (erg. less than 105 micro-
meters), the particles are coated with an insulator
such as Moo, Sue or the like, and the annealing
temperature ranges from about 420-450C.
Having thus described the invention in rather
full detail it will be understood that these details
need not be strictly adhered to but that various changes
and modifications may suggest themselves to one skilled
in the art, all falling within the scope of the invent
lion as defined by the subjoined claims.
