Stock material or miscellaneous articles – Metal continuous phase interengaged with nonmetal continuous...
Reexamination Certificate
1998-06-03
2001-01-30
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Metal continuous phase interengaged with nonmetal continuous...
C428S325000, C428S328000, C428S331000, C501S088000, C501S127000, C164S098000
Reexamination Certificate
active
06180258
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to metal matrix composites and more particularly to light-weight metal matrix composites including uniformly distributed ceramic particles which improve the thermal strength, thermal conductivity and wear resistance of the material and to methods for making the same.
BACKGROUND FOR THE INVENTION
Metal matrix composites (MMC's) are metal or alloys strengthen with tiny inclusions of another material which inhibit crack growth and increase performance. MMC's have mechanical properties that are superior to those of most pure metals, some alloys and most polymer-matrix composites, especially in high temperatures. The ability to tailor both mechanical and physical characteristic of MMC's is a unique and important feature of these materials.
Although the technology is relatively young, there are a number of sufficient applications most notably, the space shuttle fuselage struts, space telescope boom-waveguides, and diesel engines pistons. In the future, metal matrix composites are expected to become an important class of materials in numerous other commercial applications.
Although many other metal-matrix composites having widely different properties exist, some general advantages of these materials over competing materials can be cited. MMC's are known to have higher strength-to-density ratios and higher stiffness-to-density ratios with better fatigue resistances than most unreinforced metals and some polymer matrix composites.
Light weight metal composites having high tensile modulus, good ductility, toughness, formability and machine ability and methods for making the same are disclosed in my earlier U.S. Pat. No. 5,511,603. As disclosed therein, such composites include a uniform distribution of ceramic particles having an average particle size of no greater than about one micron. The metal-matrix composites disclosed therein exhibit high strength at room and elevated temperatures since the small reinforcement size and inner particle spacing meets the criteria for dispersion strengthening. The small uniformly distributed ceramic particles permit the composites to behave much more like a metal than a typical metal matrix composite, permitting their use in applications requiring greater ductility, toughness and formability. These composites also provide unexpectedly excellent machineability and ductility, even at relatively high ceramic loadings.
It is now believed that there may be a significant commercial demand for a reinforced metal matrix composite for thermal management for automotive and other applications, for example, disc brake rotors and brake drums. For such applications, the materials need high wear resistance and high thermal conductivity. It is also desirable that such materials are readily castable using available technology at a competitive cost. Accordingly, there is a need for economically producing metal-ceramic composites without expensive heavy press machinery and complicated processing techniques.
BRIEF SUMMARY OF THE INVENTION
The present invention contemplates a metal-matrix composite comprising a bimodal distribution of ceramic particles which are uniformly distributed throughout a metal or alloy matrix. The ceramic particles may comprise borides, carbides, oxides, nitrites, etc. the bimodal distribution includes a first component of ceramic particles having an average particle size of less than one micron and a second component having an average particle size of between about 5 to 15 microns. As contemplated by the invention, the metal matrix composite includes from between about 15 to 30% by weight of the first component and from about 2½ to 10% by weight of the second component. It is also presently believed that a larger volume of smaller particles may be preferred for enhanced wear resistance.
The invention also contemplates a method for forming a light weight metal matrix composite which includes a uniform distribution of ceramic particles throughout the metal or alloy matrix. The method includes the step of forming a slurry of ceramic particles in a liquid wherein about 75% of the particles have a particle size of less than one micron and about 25% of the particles have an average particle size of between about 10 to 15 microns. The ceramic particles are then separated from the liquid to provide a ceramic preform having a substantially uniformed distribution of particles and sintering the particles to one another. The ceramic preform is then placed in a mold and infused with a molten metal or alloy. The molten metal is then allowed to solidify to thereby form a light-weight metal-matrix composite.
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patent: 5511603 (1996-04-01), Brown et al.
patent: 5702542 (1997-12-01), Brown et al.
patent: 5840221 (1998-11-01), Lau et al.
Chesapeake Composites Corporation
Dougherty & Troxell
Jones Deborah
Savage Jason
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