Diamondlike Flake Composites

This invention is concerned with producing a unique composite material that utilizes diamondlike carbon flakes as the filler material. The properties of the flakes used as a filler in the composite material produce desirable thermal, electrical, mechanical, and tribological properties when used in aerospace structures and components.

Previous composite materials were made from fibers, fiber bundles, and woven fiber bundles as the strength providing component in a composite material. Fibers of graphite, boron, tungsten, and glass have been used frequently in conjunction with various organic and metallic binders. Oftentimes these materials did not have the high tensile strength and other properties required of the composite material.

Aisenberg U.S. Pat. No. 3,961,103 discloses the deposition of a carbon-diamond film on a substrate by ionizing and electrostically accelerating a beam of atomic particles of carbon. A plasma ion source produces plasma which contains large concentrations of ions of the species that is to be deposited on substrate.

Eckel et al U.S. Pat. No. 4,288,353 discloses a composite contact paste produced by mixing solid constituents in the form of graphite and metal powder with a binder comprising a mixture of epoxy resin and tar. The metal powders selected from a group include iron, aluminum, copper and alloys thereof. The resulting paste has electrical and thermal conductivity corresponding to that of carbon blocks. Neither this patent nor the Aisenberg patent is concerned with simultaneously ion beam sputtering and vacuum arc depositing to produce diamondlike flakes.

Nelson et al U.S. Pat. No. 4,191,735 discloses a method for producing synthetic diamonds utilizing an ion source from which ions of carbon and oxygen are extracted and passed through a magnetic field. This separates the carbon and oxygen beams by virtue of the different masses. A flux of carbon ions is thus produced having a sufficient energy to penetrate a diamond crystal and cause crystal growth which is predominantly internal.

British U.S. Pat. No. 1,008,618 is directed to a device for producing synthetic diamonds produced by the absorption of energies supplied by a laser beam adapted to converge upon a glass plate containing graphite inclusions. These inclusions are situated at the focal point of the optical system through which the laser beam passes, and a diamond crystal is produced by the absorption of energy supplied by the laser beam.

Both the Nelson et al patent and the British patent disclose the broad concept of utilizing a carbon ion beam or laser beam respectively, which is focused on the target to produce synthetic diamonds. These patents, however, do not disclose simultaneously ion beam sputtering and vacuum carbon arc depositing to produce diamondlike flakes.

A unique composite material is produced in accordance with the present invention. Diamondlike carbon flakes are utilized as a filler material with a variety of organic or metallic binders.

The diamondlike carbon flakes are produced by the vacuum arc deposition of carbon on a smooth surface that is simultaneously ion beam sputtered. The bombarding ions have sufficient energy to create diamond bonds. As the carbon deposit on the target thickens, spalling occurs and the diamondlike carbon flakes are collected in a receiving container.

The flakes are mixed with a binder or matrix such as epoxy or aluminum. The composite material produced has desirable thermal, electrical, and mechanical properties.

The details of the invention will be described in connection with the accompanying drawing which is a schematic view showing the apparatus for producing diamondlike carbon flakes in accordance with the present invention.

Referring now to the drawing, there is shown a target 10 that is exposed to a beam 12 of 50 eV to 3000 eV argon ions at current densities of 0.1 mA/cm.sup.2 to 20 mA/cm.sup.2. The argon ion beam 12 is furnished by an electron bombardment ion source 14 of the type developed for electronic propulsion technology.

Argon gas from a suitable source, not shown, is fed through a line 16 to a cathode 18 where the gas is ionized. The argon ions are retained within a chamber containing an anode 20 about its outer periphery. Such an ion source is described in "Advances in Electronics and Electron Physics" by H. R. Kaufman, vol. 36, pages 365-373. It will be appreciated that other gasses, in addition to argon, can be used to form the bombarding ions in the beam 12. For example, xenon and hydrogen may be used, and even vaporized carbon may be provided in the ion source 14.

Extraction of the beam 12 is accomplished by a two grid ion optics system 22. Such a system is described in AIAA Paper No. 76-1017 entitled "A 30 cm Diameter Argon Ion Source". Such a double grid system includes both a screen grid and an accelerator grid. The screen grid serves to contain the discharge plasma while forming the necessary ion optics to prevent direct impingement of accelerated ions onto the accelerator grid. Ions in the near vicinity of the screen grid have a high probability of being accelerated through the openings in the screen and the accelerator grids because of the high electric fields present at the grids.

Neutralization of the ions is achieved by the interjection of electrons into the beam 12. A suitable neutralizer 24 in the form of a downstream cathode provides these electrons.

The electron bombardment ion source 14 is located in a vacuum facility which is sufficiently large to prevent back sputtered facility material from contaminating the process. The operating pressure within the vacuum facility during sputtering is about 1.times.10.sup.-4 torr or lower.

According to the present invention, diamondlike carbon flakes 26 are produced by carbon deposition on a smooth surface of the target 10 that is simultaneously being ion beam sputter bombarded by the beam 12. This carbon deposition is produced by a vacuum arc between a carbon rod cathode 28 and an annular carbon anode 30 that are connected to a suitable power supply 32. A striker wand 34 is provided to initiate the arc in a manner well known in the art.

The carbon rod cathode 28 and anode 30 are likewise positioned within the vacuum chamber. The target 10 is positioned within 50 centimeters of both the ion source 14 and the arc produced by the electrodes 28 and 30.

The vacuum carbon arc has a low voltage between 20 and 40 volts produced by the power supply 32. This arc also has a high current discharge between 25 and 200 amperes. It is contemplated that automatic feed means may be provided for the carbon rod 28 to maintain the arc.

In operation carbon vapor as well as carbon ions will leave the tip of the carbon rod cathode 28, and a portion of these will arrive at the deposition surface of the target 10 and remain there. The bombarding argon ions in the beam 12 have sufficient energy to create diamond sp.sup.3 bonds in the carbon coating 36 being deposited by the vaccum arc. As the deposited carbon 36 thickens on the deposition target 10, spalling will occur due to the stresses in this deposit.

The spalled flakes 26 are then collected as they fall into a receiving container 38. The flakes 26 will vary from less than 0.1 microns in thickness to several microns thick. The shapes of the flakes 26 are normally random; however, it is contemplated that a texture patterned or embossed deposition target 10 may provide some control of the flake shape and size.

The collected flakes are then mixed with or joined by a matrix or binder from a reservoir 40. A variety of low viscosity organic binders, such as epoxys, may be used. The binder is then cured or hardened to form a composite material 42. It is contemplated that a low melting temperature metallic matrix, such as aluminum, may likewise be used. The composite material is formed when the metallic binder cools.

Ideally, the percentage of diamondlike flakes 26 in the composite material 42 is maximized to fully utilize their unique properties. This is achieved by using binders that have both low viscosities and low melting temperatures. Such binders not only wet the flakes, but also accommodate the greatest amount of flakes in a given volume of composite.

Typically, the diamondlike composite material 42 produced by this simultaneous sputter etching and deposition is insulating, extremely hard, semitransparent, and resistant to acids that can normally etch graphite. It is evident that extremely hard diamondlike carbon flakes 26 are produced by this process, rather than softer and lower strength graphite. The unique properties of these diamondlike carbon flakes 26 result in the superior composite material 42. It is contemplated that the carbon rod 28 may be doped to produce semiconducting flakes or other doped flake properties.

While the preferred embodiment of the invention has been disclosed and described it will be apparent that various modifications may be made to the apparatus and process without departing from the spirit of the invention or the scope of the subjoined claims. By way of example, other techniques can be employed to produce a carbon deposit 36 on the deposition target surface 10. Electron beam evaporation, laser beam evaporation, and electro-thermal evaporation may be used. Also, organic gasses may be brought into the vacuum chamber toward the deposition target 10, and these gasses would condense on this target if active cooling is used to hold the temperature low enough. In addition, a shutter or chopper may be placed between the carbon source and the deposition target to reduce or regulate the ratio of arrival of carbon atoms to beam ions. It is further contemplated that the carbon deposit 36 could be formed without simultaneously sputter etching the target 10 in certain applications.