Note: Descriptions are shown in the official language in which they were submitted.
10790~
I~AC'~DnD OE IUE INVENTION
The quick bond process described in U.S. Patent 3,~84,043
was developed to make possible the manufacture in air of an
aluminum matrix composite reinforced by a plurality of
parallel layers of unidirectional filaments. This "air
bonding" process comprises positioning a plurality of fila-
ment reinforced aluminum matrix monolayer tapes in a stack
and then pressing the stack between heated platens or dies
at high pressure in air to densify the matrix, the platen
temperature causing bonding of the matrix to the filaments.
It was believed, in this patent, that-the monolayer tapes
were best made by bonding the layer of filaments to an
aluminum backing foil by a plasma sprayed metal coating,
such as aluminum, on the surface of the filaments opposite
to the foil. It was hoped that other less expensive forms
of tapes could be developed that would produce equally
acceptable matrix composites.
SUMMARY OF THE INVENTION
A feature of this invention is a monolayer filament tape
consisting of collimated fibers, preferably boron, with in
some cases a silicon coating, held in collimated form by
metal wires woven with the fibers. This tape is then inter-
leaved with sheets of aluminum foil in making a stacked high
strength matrix composite that is bonded together and
densified by compacting it between heated platens at a high -
pressure and at a temperature below the liquidus temperature
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107gO~l
of the aluminum matrix. With this tape, the compacting and
bonding may be done in air, as in the process of the above
patent, thereby avoiding the necessity for a vacuum chamber
for the compaction and bon~ing as well as avoiding the long
time cycle required for vacuum pump-down and subsequent heat-
ing in a vacuum or inert atmosphere.
According to the present invention, the tape is pro-
duced by forming a single layer of collimated fibers and inter-
weaving with them, crosswise metal wires which serve to hold
the fibers in the single layer collimated condition during
assembly with layers of aluminum foil in making the multi-
layer composite. me interwoven wires are spaced from one
another and a minimum number of these crosswires are utilized,
only enough to permit handling of the collimated layer with-
out affecting its integrity.
In accoxdance with a particular embodiment of one
aspect of the invention there is provided, in a manufacturing
of a composite structure having an aluminum matrix with a
plurality of layerQ of high strength filaments therein, the
steps of: forming a mat consisting of a single layer of coll-
imated filaments held in mat form by aluminum crosswires inter-
woven with said filaments, assembling a plurality of these
mats with interleaved aluminum sheets to form a stack, and
densifying and bonding the stack of sheets and mats in air
to form a composite with the crosswires becoming a part of
the aluminum matrix.
In accordance with the invention, and from a
different aspect thereof, a composite includes: a plurality of
tapes each consisting of a collimated single layer of parallel
filaments and crosswires spaced apart and interwoven with said
filaments to hold the filaments in a collimated, single layer,
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107901~
mat form, a plurality of layers interleaved with the plurality
of tapes to form a stack consisting of alternate layers of
foil with layers of tape therebetween, said stack being heated
and compacted in air to press the foil around the filaments
of the several layers and to cause bonding of the adjacent foil
layers to one another between the filaments and to the fil-
- aments to produce the densified composite.
The foregoing and other objects, features, and ad-
vantages of the present invention will become more apparent
in the light of the following detailed description of pre-
ferred embodiments thereof as shown in the accompanying draw-
ing.
BRIEF DESCRIPTION OF THE DRAWq~G
Fig. 1 is an enlarged perspective view of the tape.
Fig. 2 is an enlarged end view of a stack of tapes.
Fig. 3 is an enlarged end view of a completed
composite.
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1079011
DESCRIPTION OF THE PREFERRED EMBODIl!~NT
A particular method for assembly and bonding of a
plurality of stacked tapes is described in the above-
identified patent 3,984,043, where the assembly, densifica-
tion, and bonding are all carried out in air thereby being
a low-cost, quick bond with fewer limitations on the finished
size of the composite. By this process the finished size is
limited only by the size of the press available and not by
the size of available vacuum chambers which were necessary
previously as the densification and bonding were done in a
vacuum. The tape of this invention is a simple form of tape
that is particularly usable in this process and which itself
is simple to produce and inexpensive. This tape can be used
in the air bonding process to produce an acceptable com-
posite structure of adequate strength.
To produce this tape, a plurality of filaments or fibers
2, for example boron fibers, silicon carbide fibers, or
silicon coated boron fibers, are collimated in a single
layer, as shown in Fig. 1. These filaments in the layer
are not in contact with one another and are held in the
desired spaced relation and in the single layer configura-
tion by crosswires 4 woven with the fibers, preferably at
90 to the fibers, and in spaced relation to one another.
Only enough of these crosswires are used as are needed to
hold the fibers in position as the tapes are handled in
making the composite. These crosswires are preferably
metallic and may be of aluminum to bond with the aluminum
1079011
of the interleaved foils in forming the composite. This tape
differs from the usual tape in that it has no matrix as such.
The tape is solely the fibers and the interwoven support
wires. The usual aluminum foil backing sheet is not needed.
In use the aluminum for the matrix of the composite is
provided by interleaving sheets 6 of aluminum foil between
adjacent tape layers 8, Fig. 2. This arrangement permits a
faster assembly of the several tapes or sheets for the
multilayer composite and permits a better control of the
percentage of matrix in the completed composite structure,
since thicker or thinner aluminum foil sheets may be inter-
leaved with the tapes or the number of interleaved foil
sheets may be varied to produce the proper percentage of
aluminum matrix.
The completed tapes, that is the fibers and the inter-
woven crosswires are cut to appropriate sized strips for
stacking with the interleaved foil sheets to build up the
composite structure or stack 10, Fig. 2, and the assembled
stack is then heated and densified by compression between
heated platens or dies in a press, as described in the
above-identified patent, to form the completed composite 12,
Fig. 3. The deformation of the aluminum foil sheets during
compaction, and the heating of the composite to a tempera-
ture nearly the liquidus temperature of the foils assures a
bonding of the aluminum foils to one another and to the
fibers of the several tapes. The aluminum corsswires
become an integral part of the matrix during the compaction
and bonding under pressure.
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1079011
It was expected that the fibers would oxidize during
the assembly and densification because there was no coating
on the fibers to prevent oxidation as in the plasma sprayed
tapes. High strength composites were achieved, however, even
without the protection against oxidation. It was found
desirable to minimize the assembly time for the composite
and also to minimize the time prior to the application of
pressure on the composite after positioning the composite
between the heated platens. It was found that adequate
strength in the composite could be obtained with a tape of
this character and even with the densification and bonding
occurring in air. It is believed that the minimum of oxida-
tion that occurs in the process is not detrimental and the
loss of fiber strength due to oxidation may be reversible
and may in fact produce a stronger fiber if the extent of
the oxidation is limited by the time involved in the
densification and bonding.
These tapes and the resultant composite are signifi-
cantly lower in cost tha~ the plasma sprayed tapes described
in said application. It was originally expected that this
woven mat type of tape would prove unusable in air bonding
because 1) of the oxidation of the fibers since there was no
coating on the fibers that would be impervious to air and
2) the matrix would not bond because of the oxide on the
fibers.
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10790~1
Neither of these pro~lems appears to be serious. As
above stated, by minimizing the time prior to the application
of pressure in the press any oxidation has been minimized.
Further, the a~ount of oxidation that takes place does not
appear to reduce significantly the fiber strength. The
ability to handle the woven mats of fibers independently of
the aluminum foil sheets making up the matrix has facilitated -
the stacking of the mats and foils in making the composite
and has also permitted a control of the percentage of matrix
in the completed composite.
The results of tests showed these mat tapes to be com- -
parable to the plasma sprayed tapes of the above patent when
in the completed composite structure, as shown in the
following comparison:
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1079011
The 5056 wire is an aluminum wire 0.002 inch in diameter
and these wires were spaced apart about 0.25 inch in the tape
or mat. The "tape" fiber strength is the strength of the
tape fiber before being made into the composite, the
"composite" fiber strength is that of a fiber extracted from
the composite. The "measured't bending strength is determined
by experiment and the 50% bend strength is determined by
calculation, based on the assumption of 50% fibers by volume
in the composite and utilization of the measured strength.
The data was obtained from composites made as above
described and bonded in air. The fiber strengths and
torsional performances all indicated excellent material
strength in the finished product as compared with the plasma
sprayed composites. The composite structures made with the
woven mat fibers were shown to be adequate for any of the
presently known uses for this type of composite.
When the stack of tapes is completed, the top of the
stack is preferably covered by a layer of foil 14 to form
a covering for the exposed fibers of the top tape or tapes
in the stack. This top layer of foil serves to protect
these fibers from oxidation during heating and compaction;
and when the compaction is completed, this top foil is -
bonded to the adjacent foil and to the enclosed fibers in
the same manner as the interleaved foils between the tapes.
It will be understood that a stack may in certain
instances consist of a single tape with foil on each side
where the thickness of the completed compacted composite
does not permit more than the-single layer of tape. Whether
107901~
the composite is made from a single tape stack or a multitape
stack, the crosswires of the tape, if aluminum, are incor-
porated into and become an integral part of the matrix. In
this way the composite, when densified and bonded, consists
of the filaments and matrix; the wires having served their
purpose having disappeared into the matrix.
Although the invention has been shown and described
with respect to a preferred embodiment thereof, it should be
understood by those skilled in the art that other various
changes and omissions in the form and detail thereof may be
made therein without departing from the spirit and the scope
of the invention.
CLAIMS
H~ving thus described a typical embodiment of my
invention, that which I claim as new and desire to secure
by Letters Patent of the United States is:
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