Patent Application
20050186104
The present invention relates generally to composite materials containing a nanostructured carbon binder phase, and more particularly to composite materials containing a matrix phase interspersed with a nanostructured carbon binder phase, and to a pressure-sintering process for making the same.
Research in advanced composite materials has yielded a substantial range of remarkable and diverse products. Advanced composite materials typically exhibit properties including high strength and high stiffness, low weight, corrosion resistance, and even special electrical properties in certain materials. The combination of properties have made advanced composite materials useful for various applications including aircraft and aerospace structural parts, exhaust systems, machine tools, armor plates, chemical- and heat-resistant protective coatings, and the like.
Composite materials are grouped generally into three basic groups depending on the corresponding matrix phase composed of a material selected from polymers, metals, and/or ceramics. Manufacturing and sale of composite materials represent a multi-billion dollar industry that provides a range of materials for products from high performance sports equipment to aerospace components. A common composite material is the carbon/carbon composite, which is typically composed of a matrix phase comprising carbon fibers and a binder phase in the form of a graphitized resin for providing strength and rigidity. These composites represent special materials that exhibit high specific strength and toughness, while providing good resistance to heat. These materials can be suitably used in high temperature applications such as, for example, heat shields for re-entry vehicles, braking components, radiators and heat sinks.
Such carbon composites typically can be made either through standard impregnation processes or chemical vapor infiltration (CVI) processes. The impregnation process typically takes preforms of carbon fibers, impregnates them with resin or pitch, followed by carbonization and graphitization. Both the impregnated resin and pitch shrink during the carbonization and graphitization steps, necessitating several cycles of impregnation and carbonization to obtain dense carbon composites. The carbonization and graphitization process is typically carried out through pyrolysis (chemical change via heating) of the resin at relatively high temperatures, for example, in the range of from about 500° C. to 3,000° C. depending on the corresponding process implemented.
The chemical vapor deposition process has become one of the most common processes for fabricating carbon composites. The main disadvantages of this process are long processing times (500 to 600 hours), the presence of closed porosity, low strength, broad density gradients, and the need to machine the outer impermeable skin from the composite to facilitate infiltration. Accordingly, the processes used to fabricate the composite materials can be both expensive, labor intensive and time-consuming to carry out.
Accordingly, there is a need to develop a composite material that exhibits enhanced structural properties over the composites described in the prior art while substantially reducing the time and cost needed for production. It would be highly desirable to develop a composite material containing a matrix phase interspersed with a nanostructured carbon binder phase, wherein the matrix phase can be composed of a material such as a ceramic, a metal, or combinations thereof. There is a further need for a process of fabricating such composite materials using existing reagents and equipment commercially available and which can be performed in an environmentally compatible, cost efficient and simple manner.
The present invention is directed generally to composite materials and process for making the same. The composite materials of the present invention exhibit desirable properties including high strength and low weight, and are simpler and more cost efficient to fabricate than composite materials possessing similar properties. The processes of the present invention have been found to afford considerable flexibility in tailoring the properties of the resulting composite materials to meet the performance requirements of a range of applications, such as rocket parts, exhaust systems, aerospace structures, machine tools, armor plates, and protective coatings. The composite materials of the present invention can be in the form of, for example, particle-strengthened materials, fiber-strengthened materials, network-strengthened materials, and bi-/tri-continuous-strengthened materials.
The composite materials of the present invention are generally composed of a matrix phase or preform selected from materials such as ceramics, metals or combinations thereof, with a nanostructured carbon binder phase interspersed throughout the matrix phase to provide strength and ensure the integrity of the resulting material. The nanostructured carbon binder phase is derived from a carbon binder mixture substantially composed of carbon nanoparticles. A pressure-assisted sintering process is used to distribute and uniformly infuse the carbon binder mixture into the matrix phase, which the resulting combination is thereafter sintered to polymerize the carbon binder mixture and yield a nanostructured carbon binder phase. The carbon nanoparticles used in the present invention may be selected from fullerenes and mixtures thereof.
Upon pressure-assisted sintering, the resulting composite material containing the newly formed nanostructured carbon binder phase exhibits high specific strength and toughness, low weight and good thermal stability, while imparting resilience to the material. The fabrication process requires a relatively short period of time to complete. Optionally, the carbon binder mixture can further contain other forms of carbon including, for example, pitch carbon, anthracite carbon, diamond, graphite, carbon fibers, and the like. The other forms of carbon can be present in the carbon binder mixture in amounts ranging from about 1.0% to 99% weight based on the total weight of the carbon binder mixture.
The composite materials of the present invention exhibit advantages including relative ease in sufficiently infiltrating the open pore space of the matrix phase or preform, relatively short processing time, flexibility in control of bonding between the matrix phase and the nanostructured carbon binder phase, and process scalability at economical cost.
In one aspect of the present invention, there is provided a composite material, which comprises a matrix phase having a nanostructured carbon binder phase derived from a carbon binder mixture comprising mixed fullerenes, interspersed throughout the matrix phase.
In another aspect of the present invention, there is provided a method of making a composite material which comprises the steps of:
The immediately previous method may, prior to the applying step, further include the step of applying a sufficient dispersing pressure to the carbon binder mixture and the matrix phase at a dispersing temperature for a sufficient time to facilitate diffusion or dispersal of the carbon nanoparticles throughout the matrix phase.
Various embodiments of the invention are described in detail below with reference to the drawings, in which like items are identified by the same reference designations, wherein:
The present invention is generally directed to a composite material produced from a starting material composed of a matrix phase in combination with a carbon binder mixture comprising carbon nanoparticles. The starting material is thereafter treated under suitable conditions to polymerize the carbon nanoparticles into a carbon binder phase comprising a relatively hard nanostructured carbon material, thereby yielding the composite material of the present invention. The treatment comprises a pressure-assisted sintering process that is carried out under elevated pressure at an elevated temperature for a sufficient time to induce the carbon nanoparticles to polymerize. The resulting composite material exhibits high hardness, compressive strength and stiffness, and enhanced fracture resistance, which has been found to correspond to the cohesive strength of the interphase interfaces in the composite material. The approach of the present invention affords considerable flexibility in tailoring the properties of the novel composite materials to the performance needs of various applications, such as rocket parts, exhaust systems, aerospace structures, machine tools, armor plates, and protective coatings. The composite materials of the present invention can readily be fabricated in a cost effective manner using conventional commercially available equipment and materials.
In a particular aspect of the present invention, there is disclosed a new class of composite materials, including particle-, fiber-, and network-, bi-/tri-continuous-strengthened forms (see
The metals can include iron, nickel, cobalt, titanium, aluminum, beryllium, copper, silver, gold, platinum, tungsten, molybdenum, uranium, and the like, and alloys thereof. The ceramics can include carbides, nitrides, silicides, oxides, silica, alumina, zirconia, yttria, magnesia, beryllia, titanium carbide, beryllium carbide, baron carbide, boron nitrides, silicon carbide, silicon nitride, titanium boxide, tungsten carbide, uranium carbide, and the like, and mixtures thereof. The amount of matrix phase present in the composite material can range from 1 to 99% by weight based on the total weight of the composite material.
An example of parameters applicable for the sintering process include a pressure ranging from a pressure of at least 0.1 GPa, preferably from about 0.1 GPa to 10.0 GPa, and more preferably from about 0.1 to 1.0 GPa at a sustained temperature of at least 400° C., preferably from about 400° C. to 1000° C., with processing times of from about 100 to 10,000 seconds. Applicants have found that sintering a carbon binder mixture comprising fullerenes at a pressure of about 1.0 GPa and a temperature of about 800° C. yielded a nanostructured carbon binder phase exhibiting a hardness level comparable to silicon carbide, while sintering the carbon binder mixture comprising fullerenes at a pressure of about 0.1 GPa and a temperature of about 1000° C. yields a nanostructured carbon binder phase exhibiting a hardness level comparable to steel.
The term “carbon nanoparticles” is used to encompass a class of carbon substantially spherically shaped particles of from about 0.71 to 20 nm size, so called fullerenes, such as, for example, C60, C70, C120, and the like, and mixtures thereof. A “fullerene” is a form of carbon composed of clusters of sixty carbon atoms (C60) or more bonded together in a polyhedral structure composed of pentagons and hexagons. A “nanotube” is a form of carbon composed of cluster of carbon bonded together in a substantially cylindrical structure with a diameter of a few nanometers.
Carbon nanoparticles particularly fullerene (C60) can be crystallized into a face-centered cubic structure to yield fullerite, which is generally a black crystalline solid, soluble in toluene, for example. This form or phase of carbon is thermodynamically unstable at high pressure and temperature, and tends to convert to a different form of carbon. When fullerenes and nanotubes are consolidated in the presence of moderate to high pressure and elevated temperature, they form into a nanostructured form of carbon exhibiting a hardness value comparable to silicon carbide, and at higher pressures, exhibiting a hardness value comparable to diamond.
Carbon nanoparticles (i.e., fullerenes, nanotubes, and the like) can be readily produced by inducing an electric arc struck between graphite electrodes in the presence of an inert atmosphere contained within a water-cooled chamber. The electric-arc method of producing C60 also yields a smaller number of fullerenes such as C70, C76, C78, C84, C90, . . . C120, and similar higher number carbon compounds, which have less symmetrical molecular structures. The soot-like product consists of a mixture of graphite particles and carbon nanoparticles (i.e., fullerenes, nanotubes, and the like). Generally, the carbon nanoparticles can be readily separated from the larger graphite particles by placing the mixture into a suitable liquid hydrocarbon solvent such as toluene, which is able to dissolve the carbon nanoparticles while leaving the larger graphite particles solid and intact. As the carbon nanoparticles solubulize into the solvent (e.g., toluene), the larger graphite particles settle out. The solution can then be filtered to remove the graphitic particles and the dissolved carbon nanoparticles can then be extracted from the filtrate. Further separation can be optionally accomplished through liquid chromatography techniques as known in the art.
The terms “pressure sintering” or “pressure-assisted sintering” refer generally to the process of heating and compacting a material at relatively high pressure at a temperature below its melting point to weld discrete components (i.e., matrix phase and carbon binder mixture) together to yield an intact rigid composite material of the present invention as disclosed hereinafter.
As discussed above, current practice for fabricating composites containing a carbon-based packing material have been implemented typically through the use of chemical vapor infiltration (CVI) of preforms or matrix phase. Although CVI has been proven to be a reliable technology, the CVI process, which is only capable of producing graphite, is relatively slow and labor intensive which may require several days to complete. Additionally, problems including uneven densification of the carbon infiltrant and closed porosity of the preform, which adversely affects the mechanical properties of the final product, are typically associated with the CVI process. To overcome the limitations of the prior art, Applicants have investigated a novel approach of infiltrating preforms with carbon nanoparticles selected from fullerenes, and the like, and combinations thereof. Carbon nanoparticles have the capability due largely in part to their molecular dimensions to fill and occupy open porosity in the preform. Upon infiltration, the carbon nanoparticles are transformed through pressure-assisted sintering into a hard and tough carbon binder phase in bonded association with the preform to readily yield the composite material of the present invention.
Accordingly, a feature of the processing route described herein is the use of carbon nanoparticles (i.e., fullerenes) as one of the starting materials for processing through pressure-assisted sintering, or hot pressing. Subsequently, during hot pressing, it is believed that the simultaneous application of high pressure and temperature, acting on the carbon nanoparticles, is the key to the formation of the nanostructured carbon binder phase. In addition to the corresponding pressure and temperature conditions, the holding time, which must be sufficient to enable completion of the sintering process, involving cross-linking of the carbon nanoparticles (i.e., fullerenes) to form a nanostructured form of carbon referred herein as the “carbon binder phase.” Applicants hypothesize that the high hardness displayed by the nanostructured carbon binder phase is due to the formation of mixed sp2 and sp3 bonds in the cross-linked structure, with a preponderance of sp3 bonds, while surprisingly retaining the resilience of a polymer-based material.
Pressure-assisted sintering for producing the composite materials of the present invention can be accomplished in several ways. When sintering pressure is less than 0.3 GPa, the present composite materials can be fabricated by conventional hot isostatic pressing (HIP) technology. For pressures greater than 0.3 GPa, it is preferable to utilize a uniaxial-type of hot pressing unit, which are widely known in the art. For those skilled in the art, it will be recognized that scaling present high-pressure technology to fabricate large flat panels or massive monolithic pieces can be readily accomplished.
Applicants have discovered that carbon nanoparticles such as a mixture of fullerenes can be pressure sintered in relatively large volumes at a pressure of at least 0.1 GPa, preferably ranging from about 0.1 to 10.0 GPa, and at a temperature of, for example, from about 400° C. to 1000° C., to yield the desired novel nanostructured carbon binder phase exhibiting physical properties on a scale between graphite and diamond.
Prior to pressure sintering the matrix phase containing the carbon binder mixture, the carbon binder mixture can be infiltrated into the matrix phase by applying a sufficient infiltration pressure at a suitable elevated temperature to enhance the fluidity of the mixture, and thus better facilitating the even penetration of the carbon binder mixture into the matrix phase. By applying the sufficient infiltration pressure and elevated temperature, the carbon nanoparticles has been found to readily infiltrate and permeate through the pores and spaces within the matrix phase. The infiltration pressure is generally at least 0.01 GPa, and preferably from about 0.01 GPa to 0.1 GPa and the elevated temperature is generally at least 20° C., preferably from about 20° C. to 100° C., depending on the desired achievement of the viscosity of the carbon binder mixture formed from carbon nanoparticles, and optional additional carbon material or compounds which can be carbonized or graphitized. The additional carbon material can be aromatic hydrocarbons, diamond, graphite, amorphous, nanotubes, and the like. Such aromatic hydrocarbons can be coal-tar pitch, petroleum pitch, anthracene, naphthalene and the like, and mixtures thereof.
In one embodiment of the present invention, the novel nanostructured carbon binder phase exhibits a hardness of at least four on the Mohs scale, and more specifically from about four to nine on the Mohs scale. The novel nanostructured carbon binder phase further exhibits an apparent density of from about 1.6 to 2.3 g/cm3, and a resistivity in the range of from about 0.1 to 1.0 ohm.cm. Furthermore, the nanostructured carbon binder phase exhibits a resilience of at least 2% strain to fracture, which is a surprising characteristic for a material of such relative hardness.
In the present invention, the carbon nanoparticles, including fullerenes, and the like, and mixtures thereof, are utilized as infiltrants in the fabrication of the novel composite materials of any form including, but not limited to, particle-strengthened composites, fiber-strengthened composites, network-strengthened composites and bi-/tri-continuous-strengthened composites. Carbon nanoparticles are excellent infiltrants due in part to their desirable small molecular dimensions, and their capacity to fill all open porosity of the corresponding matrix phase, whatever size and shape. The composite materials of the present invention are fabricated by pressure sintering the carbon nanoparticle infiltrated preform or matrix phase to yield the composite material of the present invention. In a preferred embodiment, the carbon binder mixture used to produce the carbon binder phase upon pressure sintering, comprises mixed fullerenes. The term “mixed fullerenes” means a mixture of fullerenes of varying molecular weights. The use of mixed fullerenes yielded an unexpected result in providing a carbon binder phase that can be used at lower pressures compared to using highly pure C60, for example. Such use of mixed fullerenes also substantially lowers the cost for fabricating the composite material.
With reference to
Note that for the description of
Applicants have discovered that wear resistance can be enhanced by increasing the weight ratio of matrix particles 2 relative to the carbon binder mixture 4. In one preferred embodiment, the matrix particles 2 are present in amount of about 60% by weight of the starting material. Particle-strengthened composites 1 of the present invention exhibit high hardness and wear resistance, particularly those containing a high fraction of uniformly dispersed superhard matrix particles such as diamond or cubic-boron nitride. Applicants also note that the strength of the particle-strengthened composite 1 can be further enhanced by blending matrix particles 2 of varying grades or sizes to formulate the matrix phase into a high weight fraction mixture. The use of varying grades of particles 2 functions to greatly increase the packing density or solids loading of the mixture. Such particle blending is a common practice in the ceramic industry. The selection of proper grade mixtures suitable for producing particle-strengthened composites 1 with the desirable strength characteristics can readily be determined and modified by the skilled artisan in the art.
Referring to
Referring to
Referring to
In an alternative embodiment, Applicants note that both oxide and non-oxide porous ceramics, including pure compounds and their composites, can be processed to form the porous matrix structures. Applicants further note that certain ceramic materials, particularly oxide-based ceramics, have been found to react with the nanostructured carbon binder phases to yield a thin reaction layer of graphitic carbon. This thin layer of graphitic carbon located between the oxide-based ceramic and the nanostructured carbon binder phase has been found to enhance resistance to fracture. This ensures sufficient bond strength between the carbon binder phase and the matrix phase to provide effective load transfer therebetween, thus minimizing debonding at the tip of an advancing crack. In this manner, fractures can be halted at the point of origin. The increased fracture resistance is realized due to the stretched fibers exerting closure forces on the fractured portions and thus reduces the average stress intensity at the crack tip, and greatly minimizing or halting propagation of the original fracture.
In another embodiment of the present invention, the porous structure 10 can be in the form of a porous graphitic carbon which would greatly benefit in terms of material properties from infiltration of a carbon binder mixture 4 containing carbon nanoparticles and pressure sintering. The porous graphitic carbon can be produced by an arc-plasma method, or by carbonization of pitch into a coke sponge, as known to one skilled in the art, for example. Further, carbon nanoparticles can also be infiltrated into porous preforms or matrix phases of ceramic materials, including alumina, boron carbide, titanium boride, and the like, and then transformed by pressure-assisted sintering into bicontinuous-strengthened composite materials.
Samples of consolidated diamond powder containing a hard nanostructured carbon binder phase were prepared by sintering at a pressure of from about 0.1 to 3.0 GPa and at a temperature of from about 400° C. to 1000° C., with a holding time of up to about 10,000 seconds to yield a sintered product. At a pressure of about 3 GPa and temperature of about 800° C., the sintered product exhibited a hardness of about ten on the Mohs scale.
Samples of consolidated graphitic fiber containing a combination of graphitic fibers and a hard nanostructured carbon binder phase were prepared by sintering at a pressure of from about 0.1 GPa to 0.3 GPa, and at a temperature of from about 800° C., with a holding time of up to about 10,000 seconds to yield a sintered product. The hard nanostructured carbon binder phase exhibited a hardness value similar to steel. Because of its scalability, using conventional hot pressing technologies, the pressure range 0.1 GPa to 0.3 GPa is preferred.
The cylinder and ram assembly 26 further includes an oil pump 24 and a pump motor 23 for supplying the hydraulic movement. The high pressure high temperature system 19 further includes electronic control devices such as a multimeter 21, a controller 25, a multimeter 30, an electrical shunt 31, an oil pressure gauge 32, a computer 35, an electrical valve 27, and a secondary oil pump motor 33 for powering a secondary oil pump 34. The control devices and electrical components are suitably arranged as known in the art to accurately provide the proper control and programming of the pressure and temperature over time needed to yield the composite materials of the present invention.
Referring to
Accordingly, the disc-shaped sample material 48 tends to heat up uniformly via the flow of current through cylindrical graphite heater 47. The pressure in the reaction cell 37 is calibrated via known phase transitions in solid substances, for example. These transitions are revealed by changes in electrical resistivity as a function of pressure. The temperature in the reaction cell is calibrated via known values of melting temperatures of different substances under high pressure. In reaction cell 37, the resistance sharply increases during melting of the metal used for calibration. In practice, the voltage across the reaction cell 37 is gradually increased and changes in the current are measured.
In
The versatility and applicability of this invention will become more apparent when the following examples are considered.
A 50:50 (wt. %) mixture of fullerenes and diamond powder (0.5 μm) was prepared by ball milling. A green body was shaped in a die under 0.5 GPa at room temperature. It was placed into the reaction cell of the high pressure-high temperature (HPHT) chamber and sintered at a pressure of about 3 GPa, at a temperature of about 800° C. and for a holding time of about 1,000 seconds.
A 50:50 (wt. %) mixture of fullerenes and diamond powder (50 μm) was prepared by ball milling. A green body was shaped in a die under 1 MPa at room temperature. It was placed into the reaction cell of the high pressure-high temperature (HPHT) chamber and sintered at a pressure of about 3 GPa, at a temperature of about 800° C. and for a holding time of about 1,000 seconds.
A 70:30 (wt. %) mixture of diamond (50 μm) and diamond (0.5 μm)/fullerene powder was prepared by ball milling. A green body was shaped in a die under 0.1 GPa at room temperature. It was placed into the reaction cell of the high pressure-high temperature (HPHT) chamber and sintered at a pressure of about 1 GPa, at a temperature of about 700° C. and for a holding time of about 1,000 seconds.
A 50:50 (wt. %) mixture of fullerenes and TiC powder (1 μm) was prepared by ball milling. A green body was shaped in a die under 0.1 GPa at room temperature. It was placed into the reaction cell of the high pressure-high temperature (HPHT) chamber and sintered at a pressure of about 1 GPa, at a temperature of about 900° C. and for a holding time of about 100 seconds.
As in Example 4, but using powders of c-BN, SiC or other carbides (boride), instead of TiC powder.
A carbon fiber weave was infiltrated with pitch and carbonized at a pressure of about 0.1 GPa and at a temperature of about 700° C. The remaining open porosity in the composite material was infiltrated with mixed fullerenes at a pressure of about 0.1 GPa, and at a temperature of about 400° C. The nanostructured carbon binder phase was formed by sintering at a pressure of about 0.5 GPa, at a temperature of about 800° C., and for a holding time of about 1000 seconds.
A carbon fiber fabric was bonded by chemical vapor infiltration (CVI), using a methane/hydrogen precursor at a temperature of about 1,000° C. The porous composite was infiltrated with pitch at 0.1 GPa, at a temperature of about 400° C., and transformed under pressure into a coke matrix at a pressure of about 0.1 GPa, at a temperature of about 700° C., for a holding time of about 10,000 seconds. The composite was thereafter heated in vacuum at 2500° C. to graphitize the coke.
A porous C/C composite, as described in Example 7, was infiltrated with C60 plus anthracene in the liquid state under a pressure of 0.1 GPa. The binder was carbonized at a pressure of about 1 GPa, and at a temperature of about 1000° C., for a holding time of about 1000 seconds. The composite was then heated in vacuum at 2500° C. to accomplish thermal stabilization and removal of residual hydrogen.
A laminated titanium-mesh was infiltrated with mixed fullerenes at a pressure of about 0.1 GPa and at a temperature of about 400° C. The nanostructured carbon binder phase was formed by sintering at a pressure of about 1 GPa, and a temperature of about 1000° C., for a holding time of about 100 seconds.
A laminated steel-mesh structure (or any other metallic alloy wire structure) was infiltrated with mixed fullerenes, as described in Example 9. The nanostructured carbon binder phase was formed by sintering at a pressure of about 0.5 GPa, and a temperature of about 700° C., for a holding time of about 1,000 seconds.
A porous titanium body was infiltrated with a 40:60 mixture of diamond powder (0.5 μm) and fullerenes. The infiltration was executed at an infiltration pressure of about 0.1 GPa and at a temperature of about 400° C. The nanostructured carbon-diamond composite was formed by sintering at a pressure of about 1 GPa, and a temperature of about 1000° C., for a holding time of about 100 seconds.
A porous titanium body sintered on top of a bulk titanium substrate was infiltrated with a 60:40 mixture of fullerenes and TiC powder (1 μm). The infiltration was carried out at an infiltration pressure of about 0.1 GPa, and a temperature of about 400° C. The composite matrix was then sintered at a pressure of about 0.5 GPa, and a temperature of about 700° C., for a holding time of about 1,000 seconds.
A porous Al2O3, Al2O3-base, ZrO2, ZrO2-base, or other oxide ceramic, produced by incomplete sintering of nano- or micro-scale particles, was infiltrated with mixed fullerenes. The nanostructured carbon binder phase was formed by sintering at a pressure of about 0.5 GPa, and a temperature of about 700° C., for a holding time of about 1,000 seconds.
A porous TiC, TiC-base, SiC, SiC-base or other carbide ceramic, produced by incomplete sintering of nano- or micro-scale particles, was infiltrated with mixed fullerenes. The nanostructured carbon binder phase was -formed by sintering at a pressure of about 0.1 GPa, and a temperature of about 900° C., for a holding time of about 100 seconds.
A porous B4C, TiB2, or other boride ceramic, produced by incomplete sintering of nano- or micro-scale particles was infiltrated with mixed fullerenes. The nanostructured carbon binder phase was formed by pressure-assisted sintering, as in Example 14.
A porous graphitic C or diamond ceramic was infiltrated with mixed fullerenes. The nanostructured carbon binder phase was formed by pressure-assisted sintering, as in Example 14.
A porous WC/Co, TiC/Ti, UC2/U, or other ceramic, produced by incomplete solid or liquid phase sintering of nano- or micro-scale particles was infiltrated with mixed fullerenes or a diamond/fullerene mixture. The nanostructured carbon binder phase was formed by pressure-assisted sintering, as in Example 14.
A scaleable method was devised for the fabrication of a new class of carbon-ceramic composite materials of the present invention for applications in non-lubricated, thermally-resistant bearings. The composite materials were produced by pressure-assisted sintering of mixtures comprising fullerene and diamond, or fullerene and graphite particle mixtures. The resulting composite materials were observed to exhibit reduced weight, good thermal stability, good radiation resistance, hardness comparable to hardened steel, exceptional resilience, frictional resistance lower than that of graphite or diamond, and excellent polishability, thus making them attractive candidates for use in bearing applications in space vehicles and platforms.
Attempts were made to develop composite rollers and sliding fits for fabricating precision bearings. To facilitate these attempts, procedures were developed for hot pressing the hard carbon-ceramic composite materials, and thereafter grinding the resulting materials into flat, round and spherical pieces. The pieces were then polished to yield bearings possessing a super-smooth surface finish. These attempts were made to produce bearings that would conform to specific performance requirements as dictated by producers of precision bearing.
As previously noted, Applicants have observed that a carbon binder mixture containing C60 fullerene fuses under pressures of from about 1 to 10 GPa at temperatures of from about 600° C. to 1000° C. to yield an amorphous carbon phase referred herein as “Diamonite-A” which exhibits a hardness value between that exhibited by silicon carbide and diamond. Applicants further observed that a carbon binder mixture containing mixed fullerene (i.e., C60, C70, and the like) fuses at lower pressures of from about 0.1 to 1.0 GPa to yield a different form of an amorphous carbon phase referred herein as “Diamonite-B” which exhibits a hardness value between that exhibited by hardened steel and carbide.
A new class of composite materials was prepared using the mixed fullerene carbon binder mixture in combination with either diamond particles or graphite particles, respectively. Upon pressure sintering, the prepared composite materials comprising mixed fullerene carbon binder blended with a high fraction of diamond particles yielded a composite material referred herein as “Diamonite-C”. Upon pressure sintering, the prepared composite materials comprising mixed fullerene carbon binder blended with a high fraction of graphite particles yielded a composite material referred herein as “Diamonite-D”. The resulting composite materials exhibited excellent mechanical properties including high hardness, low friction and exceptional resilience. This combination of mechanical properties is unusual and atypical.
The Diamonite-C and -D were each produced by pressure-assisted sintering of mixed fullerene carbon binder phase in combination with diamond and graphite particles, respectively. In particular, Diamonite-C was prepared by ball milling mixed fullerene in an amount of about 60 percent weight with fine diamond particles, and sintering the resulting mixture at a pressure of about 2.0 GPa, and a temperature of about 800° C. for about 1,000 seconds. Diamonite-D was prepared by ball milling mixed fullerene in an amount of about 60 percent weight with fine graphite particles, and sintering the resulting mixture at a pressure of about 0.3 GPa, and a temperature of about 800° C. for about 1,000 seconds. The properties of Diamonite-A, -B, -C, and -D are listed in Table 1 below. Applicants observed the high hardness of Diamonite-C, which is comparable to that of diamond, and the exceptional thermal stability of Diamonite-D.
Because of the relatively high pressures needed to fuse and consolidate these mixtures, the maximum manufacturable size was about 10 cm for Diamonite-A and -C and about 100 cm for Diamonite-B and -D. This capability is, for example, more than sufficient for making preforms suitable for fabricating bearings of almost any desired size or shape.
A significant achievement has been the successful mechanical polishing of the composite materials of the present invention, which has permitted close examination of microstructures and allowed hardness measurements to be performed.
Referring to
Measuring the Vickers hardness of the Diamonite-C composite material was difficult due to the inability to obtain well-defined indentations irrespective of the applied load. Referring back to
The above observations, indicating that Diamonite-B phase is both hard and exceptionally resilient, prompted additional compression tests on small samples of pure Diamonite-B and Diamonite-C. These tests confirmed that Diamonite-C is stronger and stiffer than Diamonite-B, but fracture strains are comparable (about 2%) as shown in
Friction coefficients were determined using pin-on-disc and tilted-plane methods. In both tests, the measured dry friction coefficients for Diamonite-A and B, at rest and in motion, were measured to be lower that that of diamond, including diamond with a mirror-polished surface. Pin-on-disc friction experiments, performed on Diamonite-A, gave friction coefficients of 0.15 to 0.17 in humid air and 0.05 to 0.12 in dry nitrogen. On the other hand, tilted-plane friction experiments, performed on Diamonite-A, gave values of 0.07 against steel, 0.12 against Teflon, and 0.07 against graphite. The commercial implications of these findings could be quite significant for bearing and sliding fit applications.
Although various embodiments of the invention have been shown and described, they are not meant to be limiting. Those of skill in the art may recognize various modifications to these embodiments, which modifications are meant to be covered by the spirit and scope of the appended claims.
The present Application claims the benefit of U.S. Provisional Application No. 60/457,445, filed Mar. 26, 2003, entitled “DIAMOND-BONDED COMPOSITES AND METHOD FOR PRODUCTION OF SAME.”
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Grant Numbers N00014-01-C-0370 and N00014-01-1-0079 both awarded by the Office of Naval Research; by the terms of Contract Number NAS1-03045 awarded by the National Aeronautics and Space Agency; and by the terms of Contract No. DAAH01-OO-CR008 funded by U.S. Army Aviation and Missile Command.
| Number | Date | Country | |
|---|---|---|---|
| 60457445 | Mar 2003 | US |
