Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C26/00—Alloys containing diamond or cubic or wurtzitic boron nitride, fullerenes or carbon nanotubes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium

Definitions

• the present invention relates to composite materials in general, and more particularly to lightweight composite materials with very high stiffness, and to a method of making products from such materials.
• composites that are constituted by intimate mixtures or agglomerations of two or more generally disparate materials that are bonded together by other than chemical bonds and each of which contributes its inherent properties to the composite so that the overall properties of the composite material are superior to those of either of the constituent materials if it were used by itself.
• the material to be used for a particular product, component or structure is usually chosen in such a manner as to give the respective product, component or structure the attributes or properties required or expected therefrom, such as the required strength, resistance to wear, chemical attack or other external influences to which the component, product or structure is subjected or exposed when in use, and the like.
• the cost of the materials going into the product, and the cost of manufacturing the product are also important if not determinative factors in selecting the materials.
• such costs may become only secondary factors that may be outweighed by other considerations, such as the cost of bringing the product into outer space or of repeated lifting of the product when the platform carrying the same becomes airborne.
• high performance mirrors and structures must perform in a stable and reliable manner under severe thermal and/or environmental conditions which necessitate high thermal conductivity, low thermal expansion, high stiffness, and radiation hardness.
• Applications include mirrors for high energy lasers and orbital surveillance as well as aerospace and other structures requiring very high stability and/or specific stiffness (aircraft, satellites, etc.).
• the preferred materials of choice for such products are molybdenum, silicon, and silicon carbide for the laser mirrors and beryllium and silicon carbide for the aerospace applications.
• Diamond offers dramatic performance improvements over all of these materials.
• its unexcelled specific stiffness would make it desirable to use it in the construction of thermo-mechanically stable structures of the lowest possible weight.
• diamond was heretofore impossible to employ diamond as a structural material, except in some rare instances, not only because of cost concerns, but also, and probably more importantly, because there is no currently known method of synthetically producing pure diamond products of any meaningful size that would be required for such products to be employable in the above applications.
• beryllium which has the highest specific stiffness of all of the materials that are currently considered to be available for the making of products of the above type, is often resorted to for making such products.
• beryllium is also costly (albeit less so than pure diamond), and it also poses a fabrication health risk, and requires high fabrication temperatures (about 1200 o C).
• beryllium tends to crystallize in an anisotropic fashion, products such as structures, structural components, mirrors or the like that are made of this material exhibit thermal, temporal and polishing instabilities which would not be present if such products were made of or with diamond because the latter forms isotropic crystals.
• Still another object of the present invention is so to develop the material of the type here under consideration as to be suited for use in the production of a wide variety of products regardless of their sizes and/or shapes.
• a concomitant object of the present invention is to design an equipment for the performance of the method of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.
• one feature of the present invention resides in a composite material which includes a multitude of diamond particles and a matrix of a metallic material embedding the diamond particles and interconnecting the same to form therewith a solid body having a very high stiffness to weight ratio.
• a method of making a product having a very high stiffness to weight ratio including the steps of mixing diamond particles with a particulate metallic material to obtain a mixture thereof with a predetermined ratio of the diamond particles to the metallic material; confining a quantity of the mixture in an enclosed space; evacuating the enclosed space; and subjecting the quantity of the mixture confined in the evacuated enclosed space to temperature and pressure conditions sufficient to cause the metallic material to form a matrix that embeds and interconnects the diamond particles to form a solid body therewith.
• a composite material constituted by a solid mixture of diamond particles embedded in a matrix constituted by any of a variety of suitable matrix materials, preferably metals or metal alloys.
• Diamond can be mixed with many materials, including metals, with no reaction, because it is among the most chemically inert of all known materials. This property allows the formation of mixtures of diamond and other materials to form composites with very well defined constituent ratios. Mixtures are known to follow classical mixture rules which predict that properties such as expansivity, conductivity and the modulus of elasticity vary smoothly, albeit not necessarily linearly, with relative constituent ratios. When metals are used as the matrix materials, they form a high thermal and electrical conductivity matrix that embeds and positionally fixes the inert diamond particles.
• Additional materials can also be used in the mixture, and they can later be leached out to form a porous structure suitable for very high performance heat exchangers (with well defined porosity) as well as for catalytic and ion exchange structures suitable for use in environments otherwise unsuitable for organic media.
• a solid mixture of diamond powder and particles of one or more low density metals forms a family of solids with unexcelled stiffness, high thermal and electrical conductivity, low thermal expansivity and relatively low fabrication temperatures, and enables the use of such solids in structural/thermo-mechanical applications that are not achievable using other materials.
• the diamond composite is formed by mixing diamond and metal powders, sealing the mixture in an evacuated mold or other evacuated space, and subjecting the mixture to high temperature and pressure until the metal has infiltrated the interstices between the diamond particles. Then, upon cooling of the thus treated composite material, the metallic material will embed and interconnect the diamond particles, resulting in the formation of a solid body.
• the evacuated space is constituted by a mold cavity
• composites of the above type using magnesium or aluminum (convenient low density metals) for the matrix material can typically be formed or shaped at 550 o C (versus 1200 o C needed for forming products from beryllium) and 15000 psi, although lower pressures can be used. While experience indicates that the above temperature and pressure parameters are suitable when either aluminum or magnesium is employed as the matrix material, the actual choice of such parameters depends on which metal is selected to constitute the matrix, on the complexity of the shape of the product to be made, and on other criteria.
• the temperature range is the temperature at which the metal is capable of flowing at the pressure applied into the interstices between the diamond particles (generally speaking, the plastic deformation point) at the lower end, and the graphitization of the carbonaceous material of the diamond particles at the upper end.
• the preferred temperature range for aluminum or magnesium is between 500 and 1200 o C.
• the diamond volume fraction in the mixture is typically chosen to be as high as in the 80-95 percent range to assure bonding, on the one hand, and properties as close to those of pure diamond as possible or feasible.
• diamond offers dramatic improvement in component weight and thermal stability relative to other materials heretofore used for making products for similar applications. Since, as mentioned before, diamond cannot yet be fabricated in large sizes, composites offer the means to achieve most of the advantages of pure diamond, but at a cost competitive with other high performance structure materials.
• diamond-metal composites offer higher performance, lower fabrication temperatures, improved thermal and mechanical performance, lower susceptibility to thermal and temporal instabilities and no toxicity when compared to beryllium and silicon carbide which are currently considered the best materials available.
• the improved material properties provide enhancements in performance and stability, and/or a reduction in weight.
• the fact that the specific stiffness of diamond is double that of its closest competitor, beryllium, enables the use of a lighter design which, in turn, eases the launch requirements and/or allows the use of a larger, more efficient collection aperture for orbital surveillance satellites.
• the use of a diamond composite instead of beryllium would increase the payload capacity by up to 50 percent for the same total launch load. Since diamond powder costs are relatively low (about the same in terms of dollars per pound as those of zinc selenide), such composites can be used for high performance airframes, such as the national aerospace plane and hypersonic missiles, with comparable gains in payload and performance. In fact, the higher performing diamond composite would enable applications which are well beyond the capabilities of current materials and designs.
• the higher ratio of thermal conductivity to expansivity of diamond as compared with those of the other materials included in Table 1 allows the use of very high performance heat exchanger designs not available to any other material. Such devices are useful not only for cooled mirrors, but for high flux nuclear reactors, as well.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
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• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Carbon And Carbon Compounds (AREA)
• Powder Metallurgy (AREA)

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Citations (3)

• 1991
  • 1991-05-29 EP EP91108843A patent/EP0459474A1/fr not_active Withdrawn
  • 1991-05-29 JP JP3154131A patent/JPH04231436A/ja active Pending

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