US 3720257 A
A method of producing carbon fiber-reinforced metal wherein the carbon fibers are first coated with nickel, the coated fibers are then combined with a melt of the metal heated in a crucible under a vacuum or protective gaseous atmosphere to exclude the possibility of oxidation and which is then allowed to solidify. Suitable materials for the metallic melt are aluminum, copper, tin and alloys of these metals all of which meet the requirement of a melting temperature lower than that of nickel.
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Description (OCR text may contain errors)
' United States Patent 1 m1 Be'utler et al.
[ 1March 13, 1973 METHOD OF PRODUCING CARBON FIBER-REINFORCED METAL  Inventors: Hans Beutler, Sulz; Emmanuel De Lamotte Oberrohrdotf; Anthony James Perry, Nussbaumen, all of Switzerland  Assignee: Aktiengesellschalt Brown, Boveri &
Cie, Baden, Switzerland  Filed: Dec. 18, 1970  App1.No.: 99,521
 Foreign Application Priority Data Jan, 7, 1970 "Switzerland "96/70  U.S.Cl. ....l64/75, 164/100, 164/108, 29/191  Int. Cl. ..B22d 19/00  Field of Search ..164/46, 61, 66, 68, 75,100, 164/108,333;29/191,195C
[5 6] References Cited UNITED STATES PATENTS 1,314,603 9/1919 Mott ..29/195C 3,097,931 7/1963 Davidson et a1. 29/195 C 3,384,463 5/1968 Olstowski et al. ..29/l91 X 3,473,900 10/1969 Sara ..29/1)5 3,547,180 12/1970 Cochran et a1.- i i ..164/61 3,622,283 Sara ..-......29/191 C Primary Examiner-R. Spencer Annear Atlorney-Pierce, Scheffler & Parker  ABSTRACT A method of producing carbon fiber-reinforced metal wherein the carbon fibers are first coated with nickel, the coated fibers are then combined with a melt of the metal heated in a crucible under a vacuum or protec- 8-Claims, No Drawings METHOD OF PRODUCING CARBON FIBER- REINFORCED METAL troduce carbon fibers into various'metals, which did not bring, however, the expected result in most cases. This seems to be due to the difficulty of achieving a good wetting between the metallic melt and the carbon fibers. For example, attempts at casting pure aluminum or copper around commercial carbon fibers failed completely. Other methods, such as the application from the gaseous-phase, by electrolysis, or in powder form in combination with hot pressing are much more complicated and thus more expensive than melt infilmatrix, and that it is possible to produce in thismanner tration. Moreover, these methods frequently lead to mechanical, chemical or structural deterioration of the carbon fibers.
The general object of this invention is to provide a method which does not suffer from these disadvantages.
The method according to the invention is characterized in that carbon fibers, whose surface is completely covered with nickel, are surrounded with a metallic melt whose temperature is below the melting temperature of nickel, and allowed to solidify to a compound material. The molten metal consists preferably of aluminum or an aluminum alloy. Copper or tin or copper or tin alloys can also'be of advantage for certain uses.
It is advisable when joining the metal with the nickelcoated carbon fibers to keep the latter under such a vacuum or protective gas that no oxidation takes place between the individual components. Furthermore, it is of advantage to keep the time of contact between the nickel-coated carbon fibers and the surrounding metallic melt as short as possible, in order to avoid orat least reduce harmful reactions between the melt and the fibers. The invention will be described more fully on the basis of the following examples.
In order to reinforce aluminum with carbon fibers, the fibers whose starting material was polyacrylicnitrile were first provided electrolytically with a copper coat varying in thickness from 20 to 100 A in order to increase the uniformity of the fiber surface and the electric conductivity of the fibers; subsequently the fibers were covered electrolytically with a nickel coat varying in thickness between 0.l and 1 micron. Then the nickel coated fibers were brought into a crucible with aluminum pieces. The crucible was then heated to the melting point of the aluminum under a vacuum of 10" mm Hg, so that the fibers become surrounded by liquid aluminum. To keep the contact time between the fibers and the liquid metallic melt short, the temperature was brought below the melting point again after 1 to 20 seconds, to allow the aluminum to solidify again after this time. The crucible consisted of graphite and was heated electrically by current induction. The same procedures were carried out with nickel coated carbon fibers and surrounding copper, tin or aluminum-,
Tests showed that it is possible to reinforce in this manner a metal with carbon fibers without impairing the good properties of the latter, that the carbon fibers thus treated are uniformly distributed in the metal compound materials with improved properties within a wide range of specific temperatures, cooling rate and chemical composition.
When using metallic melts which yield a brittle intermediate structure when they solidify with the nickel coat of the carbon fibers, one shouldendeavor to keep the thickness of the nickel coat as small as possible. This can be achieved, for example, by depositing the nickel coat by chemical reaction from the gaseous phase. I e
The starting material of the carbon fibers is preferably polyacrylic-nitrile. The metallic melt can also contain alloying additions which reduce the specific surface tension of the melt with respect to the carbon fibers. Carbon compound materials can be used, for example, in lightconstruction, where a high specific strength is required. Examples are centrifugal motors, turbine blades, compressor blades and moving parts in looms.
Carbon fiber/copper compound materials have good electrical properties and increased strength. Examples for the use of such a material are, for example, locomotive'pantographs, trolley wires and liquid-cooled tubular conductors.
Carbon fiber/tin/alloycompound materials have increased strength and improved friction properties. Examples can be found in the highly stressed babbitbearings for diesel engines and turbo rotors.
1. The method of producing a carbon fiber-reinforced metal body which comprises the sequence of steps of enhancing the electrical conductivity of the carbon fibers by initially covering them with a copper coating having a thickness of from 20 to A; completely covering the copper-coated surfaces of the carbon fibers with a uniform layer of nickel having a thickness not greater than 1 micron; surrounding said nickel-coated carbon fibers, in a non-oxidizing environment, with a melt of a metal having a melting temperature lower than that of nickel; and solidifying the melt to a carbon fiber-reinforced metal body. I
2. The method of producing carbon fiber-reinforced metal as defined in claim 1 wherein said metallic melt is constituted by aluminum or an alloy thereof.
3. The method of producing carbon fiber-reinforced metal as defined in claim 1 wherein said metallic melt is constituted by copper or an alloy thereof.
4. The method of producing carbon fiber-reinforced metal as defined in claim 1 wherein said metallic melt is constituted by tin or an alloy thereof.
5. The method of producing carbon fiber-reinforced metal as defined in claim 1 wherein the nickel which covers the copper-coated carbon fibers has a thickness of less than 1 micron.
6. The method of producing carbon fiber-reinforced metal as defined in claim 1 wherein the step of surrounding the nickel coated carbon fibers with the metallic melt is carried out under a vacuum of at least 10" mm Hg.
7. The method of producing carbon fiber-reinforced metal as defined in claim 1 wherein the starting material for the carbon fibers is polyacrylic-nitrile.
8. The method of producing carbon fiber-reinforced metal as defined in claim 1 wherein the metallic melt includes alloying additives which serve to reduce the specific surface tension of the melt with respect to the carbon fibers.