Stock material or miscellaneous articles – All metal or with adjacent metals – Laterally noncoextensive components
Reexamination Certificate
2001-02-26
2003-02-11
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Laterally noncoextensive components
C164S066100, C164S068100, C164S069100, C164S091000, C164S094000, C164S097000, C164S101000, C428S621000, C428S627000, C428S926000
Reexamination Certificate
active
06517953
ABSTRACT:
TECHNICAL FIELD
The present invention relates to macrocomposite bodies comprising a metal or metal matrix composite substrate featuring a coating or surface layer on at least a portion thereof. In particular, the present invention relates to such surface layers or coatings whose difference in such physical properties as hardness and abrasiveness relative to the substrate increase the usefulness of the macrocomposite bodies and ease of shaping same.
BACKGROUND ART
Composite products comprising a metal matrix and a strengthening or reinforcing phase such as ceramic particulates, whiskers, fibers or the like, show great promise for a variety of applications because they combine some of the stiffness and wear resistance of the reinforcing phase with the ductility and toughness of the metal matrix. Generally, a metal matrix composite (“MMC”) will show an improvement in such properties as strength, stiffness, contact wear resistance and elevated temperature strength retention relative to the matrix metal in monolithic form, but the degree to which any given property may be improved depends largely on the specific constituents, their volume or weight fraction, and how they are processed in forming the composite. In some instances, the composite also may be lighter in weight than the matrix metal per se. Aluminum matrix composites reinforced with ceramics such as silicon carbide in particulate, platelet, or whisker form, for example, are of interest because of their high stiffness, wear resistance and high temperature strength relative to aluminum.
U.S. Pat. No. 4,600,481 to Sane et al. discloses an electrolytic aluminum production cell component comprising a preformed matrix based on various ceramic materials including aluminum nitride, the preformed matrix having voids extending throughout its structure, the voids in the preformed matrix structure being filled or substantially filled with aluminum in intimate contact with the matrix usually in wetting contact whereby the matrix will remain permanently filled with molten aluminum in the conditions of use of the cell component. According to Sane et al. once the materials have been wetted by molten aluminum the wetting contact is maintained even at lower temperatures and under an atmosphere in which wetting could not initially be established. Further, by having the aluminum in wetting contact with the matrix retention of the aluminum in the structure is assisted and a protective film of aluminum forms at the surface protecting the structure from corrosion.
The metal matrix composite materials systems which presently command the greatest interest and the greatest share of the market are those having silicon carbide or aluminum oxide particulates several microns to tens of microns in size reinforcing a matrix predominantly of aluminum. Such materials systems combine good performance in terms of physical properties with relatively low cost. Such MMC's can be rather abrasive, however, which can create wear problems in those applications where the MMC component is in sliding contact with an unreinforced metal component. Even in those applications where the contact is not in sliding contact, vibrations have the potential to cause fretting wear of the contacting parts. Moreover, most components require some amount of machining. Although “exotic” forms of machining such as water jet or laser machining are available, the machining infrastructure is still based on “traditional” machining using cutting or grinding tools. Further, sometimes only traditional machining can be used to machine certain geometries or provide a particular surface finish. The problem with the above-identified popular MMC material systems is that they tend to be difficult to machine at least with traditional cutting tools. Specifically, not only can machining stock not be removed quickly, the cutting tools become dull extremely rapidly. Whether the tools can be resharpened or must be disposed of a cost is imposed in terms of down-time to change or resharpen tools.
U.S. Pat. No. 5,511,603 to Brown et al. discloses a machinable metal matrix composite material. The inventors state that small sized particles for the reinforcement phase, no greater than about three microns in diameter and preferably less than one in conjunction with relatively low particle loading, and a substantially uniform distribution of ceramic particles in a sintered preform are all important for achieving a machinable composite material. Such metal matrix composites suffer, however, from the expense of such ultra-fine powders, the relative difficulty encountered in distributing them uniformly throughout a preform and infiltrating such preforms expeditiously.
DESCRIPTION OF COMMONLY OWNED U.S. PATENTS
Commonly owned U.S. Pat. No. 4,828,008 to White et al. teaches a technique for producing a metal matrix composite body by a spontaneous infiltration process. According to the White et al. invention, a permeable mass of ceramic filler material may be infiltrated by a molten aluminum alloy containing at least 1 weight percent magnesium in the presence of a gas comprising from about 10 to 100 volume percent nitrogen without the requirement for pressure or vacuum, whether externally applied or internally created. In one embodiment of the White et al. invention, the formed metal matrix composite body is provided with an aluminum nitride skin or surface. Specifically, if the supply of molten aluminum alloy matrix metal becomes exhausted before complete infiltration of the permeable ceramic filler material, an aluminum nitride layer or zone may form on or along the outer surface of the metal matrix composite. Also, an aluminum nitride skin can be formed at the exterior surface of the permeable mass of ceramic filler material by prolonging the process conditions. In particular, once infiltration of the permeable ceramic material is substantially complete if the infiltrated ceramic material is further exposed to the nitrogenous atmosphere at substantially the same temperature at which infiltration occurred, the molten aluminum at the exposed surface will nitride. The degree of nitridation can be controlled and may be formed as either a continuous phase or discontinuous phase in the skin layer.
Commonly owned U.S. Pat. No. 5,040,588 to Newkirk et al. teaches the production of macrocomposite bodies comprising one or more metal matrix composite bodies bonded to one or more second bodies. The second body may comprise ceramic, metal or composite bodies of ceramic and metal. In a preferred embodiment of the invention, a permeable mass or preform is placed in contact with the second body. A molten matrix metal is caused to infiltrate the permeable mass or preform up to the second body, the infiltrated mass or preform thereby becoming a metal matrix composite body. Upon solidifying the matrix metal, the formed MMC remains bonded to the second body.
Commonly owned U.S. Pat. No. 5,020,584 to Aghajanian et al. teaches the addition of matrix metal in powdered form to a permeable mass to filler material or a preform. The presence of powdered matrix metal in the preform or filler material reduces the relative volume fraction of filler material to matrix metal.
DISCLOSURE OF THE INVENTION
The present invention provides a technique for producing metal matrix composite bodies having surfaces which are easier to machine and are less abrasive in use. Machinability and wear compatibility (low abrasiveness) are important considerations in producing metal matrix composite bodies. Often, metal matrix composite bodies lack these important characteristics in part because hard ceramic materials, such as silicon carbide, are used as the reinforcement phase. The present invention addresses these problems by providing a surface layer on the MMC material which has the desired characteristics. Specifically, the surface layer is itself a MMC material comprising aluminum nitride.
To make such a metal matrix composite body, for example, a layer is provided to a permeable mass or preform at the surface or surfaces where a reduced volumetric load
Aghajanian Michael K.
Schultz Brian E.
Connolly Bove Lodge and Hutz LLP
Koehler Robert R.
Lanxide Technology Company, LP
LandOfFree
Metal matrix composite body having a surface of increased... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Metal matrix composite body having a surface of increased..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Metal matrix composite body having a surface of increased... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3166421