CA1079011A

CA1079011A - Quick bond composite and process

Info

Publication number: CA1079011A
Application number: CA290,946A
Authority: CA
Inventors: Karl M. Prewo
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1976-12-17
Filing date: 1977-11-15
Publication date: 1980-06-10
Also published as: FR2374162B1; SE7714253L; IL53515A; JPS5376905A; FR2374162A1; GB1562270A; DE2756015A1; BE861498A; IL53515A0

Abstract

QUICK BOND COMPOSITE AND PROCESS

ABSTRACT OF THE DISCLOSURE

A tape of monolayer matrix for use in making up a multilayer matrix or composite which is bonded at a high pressure and temperature by pressing the composite between heated platens in air to cause densification, the tape consisting of collimated fibers held together by metal wire woven at right angles to the fibers. The aluminum matrix in which the fibers are embedded is provided by aluminum foils alternating with the collimated fibers in the multi-layer matrix.

Description

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

-2-. .

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, ~ 3 -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.

- 3a -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 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.

.. . - - . . . . . . .

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.

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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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.

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:

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In the manufacture of a composite structure having an aluminum matrix with a plurality of layers 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 inter-leaved aluminum sheets to form a stack, and densifying and bonding the stack of sheets and mats in air to form a composite with the corsswires becoming a part of the aluminum matrix.

2. The process of claim 1 in which the densification and bonding is done by heating and pressing the stack between heated platens.

3. A composite including:
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, 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 stacks 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 filaments to produce the densified composite.

4. A composite as in claim 3 in which the crosswires and the foils are aluminum.

5. A composite as in claim 3 in which the filaments are boron.

6. A composite as in claim 4 in which the crosswires become an integral part of the matrix in the densified com-posite.