Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
2002-05-28
2004-03-09
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S294100, C428S408000, C428S698000, C428S704000, C428S426000, C266S239000, C266S282000, C501S095200, C501S099000, C192S10700R, C106S001150
Reexamination Certificate
active
06703117
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to friction or sliding bodies formed from at least two composite materials reinforced with fiber bundles and containing a ceramics matrix. A first composite material forms the outside of the sliding body and a second composite material is joined in an areal manner to the first composite material. The invention also relates to a process for the production of friction bodies or sliding bodies formed of at least two composite materials reinforced with fiber bundles and containing a ceramics matrix. Again, a first composite material forms the outside of the friction body or sliding body and a second composite material is joined in an areal manner to the first composite material.
Composite materials reinforced with high temperature resistant fibers and/or fiber bundles and containing a ceramics matrix have been known for about 10 years and are used in many applications where extremely high requirements are placed on a material, such as high temperature resistance combined with strength and ductility. Those requirements are demanded in particular of frictional or sliding partners.
The extent to which composite materials reinforced with fibers and/or fiber bundles and containing a ceramics matrix, referred to below as CMC composite materials for the sake of brevity, can be used in the sphere of applications having high temperature requirements depends not in the least on the structure of the matrix of the composite materials and in particular on the structure of their surface. As long as the matrix of the composite materials is composed of different phases, the matrix structure on the surface of the CMC composite materials can be damaged by the dissolving out of a matrix phase that melts at relatively low temperatures and that can be attacked by chemical processes such as oxidation, as a result of which the useful life of the CMC composite materials is currently restricted. Those problems become all the greater if a CMC material is, in addition, subjected to mechanical wear. In that connection, new crystallites of the matrix which are constantly being exposed can be attacked even at relatively low temperatures and those crystallites are thereby very rapidly degraded. Furthermore, interstices in the matrix composite formed by the dissolved-out crystallites provide an opportunity for increased mechanical attack.
Areas of use of CMC composite materials in which mechanical stress plays a significant role include, for example, the use of CMC elements as sliding bearing components and friction linings such as brake discs and brake linings. Initially, composite materials reinforced in particular with carbon fibers and containing a carbon matrix, so-called CFC composite materials, were used in the friction linings sector. However, those CFC composites have the disadvantage of an insufficient temperature resistance of the material to oxidative attack. Attempts have therefore been made in the meantime to replace the carbon matrix of the composite material with a more oxidation resistant matrix. In that connection, SiC matrices that are resistant to oxidation at significantly higher temperatures (1500° C.) and with or without any additional surface protective layer are used, in particular. As a result, composite materials reinforced with carbon fibers and containing an SiC matrix, referred to below as C/SiC composite materials, are nowadays mainly used for friction linings such as brake discs and brake linings.
A number of processes for producing C/SiC composite materials have been developed in the meantime, in particular also with the intention of using such materials as components of brake systems. For example, processes for the production of C/SiC composite materials are described in German Published, Non-Prosecuted Patent Application DE 197 10 105 A1, corresponding to U.S. Pat. Nos. 6,231,791 and 6,030,913, and German Patent DE 197 11 829 C1, corresponding to U.S. Pat. No. 6,261,981, in which fiber bundles provided with at least one carbon layer and/or with a reinforced binder layer are mixed with carbon-containing binders with or without fillers, following which the mixtures are compressed and hardened before being carbonized, possibly graphited, and finally infiltrated with liquid silicon. Sliding bodies and friction bodies which have also heretofore been produced from these materials, then are formed homogeneously of one material.
All sliding and friction bodies of C/SiC composite materials produced heretofore according to the above-described processes have an inhomogeneous structure of the matrix, which in the case of processes according to German Published, Non-Prosecuted Patent Application DE 197 10 105 A1, corresponding to U.S. Pat. Nos. 6,231,791 and 6,030,913, and German Patent DE 197 11 829 C1, corresponding to U.S. Pat. No. 6,261,981 is reflected in the fact that the matrix also contains phases of pure carbon and/or silicon and there is therefore not a homogeneous matrix composition. The carbon regions oxidize under relatively high temperature stress, i.e. burn-out from the composite material, and the silicon regions already melt at a temperature of about 1400° C. Accordingly, it has not heretofore been possible, using those processes, to obtain a matrix structure of C/SiC composite materials that is capable of withstanding prolonged thermal stresses at high temperatures, particularly not when exposed to additional mechanical stress. Those stresses occur in particular on the surface of the friction body or sliding body in addition to the burn-outs. As a result, the surface exhibits a rough appearance over the course of time and thus the surface available for the sliding or friction process is reduced.
In a process for the production of C/SiC composite materials described in German Published, Non-Prosecuted Patent Application DE 199 44 345 A1, corresponding to copending U.S. application Ser. No. 09/663,582, filed Sep. 18, 2000, it has for the first time become possible to produce a C/SiC composite material that has as low a proportion of the silicon and carbon phase as possible and a grain structure with cracks that do not exert a negative effect under mechanical stress. The composite material which is reinforced with fiber bundles and contains a ceramics matrix that is produced thereby, includes fiber bundles which are formed of two different fractions having different mean fiber bundle lengths. Those two fiber bundle fractions in the total fiber bundle distribution of the mass of the fiber bundles of the composite material are separated with respect to fiber bundle length by a minimum of the fiber bundle distribution. Even if the carbon fraction in the matrix has been significantly reduced in those composite materials, the problem still remains, in particular as a result of the mechanical processing of the composite materials, that free carbon regions always still exist on the surface of the composite material due to the carbon fiber bundles. As a result, the fiber bundles on the surface are burnt out under high temperature stresses in an oxidative atmosphere, which can be observed in particular after brake discs, for example, have been subjected to intensive stress.
One way of resolving that problem is for the supporting core of friction and sliding bodies to be formed of a different material than the outer friction layer, which is described, for example, in German Published, Non-Prosecuted Patent Application DE 44 38 456 A1, corresponding to U.S. Pat. No. 6,042,935. The conventionally employed CMC composite materials, for example CFC composite materials as well, can be used for the supporting core. However, the material of the outer friction layer should be modified so as to avoid a burning-out of the fiber bundles close to the surface. A first attempt in that direction is described in German Published, Non-Prosecuted Patent Application DE 198 05 868 A1, in which various compression molding materials are compressed in a single compression process to form a molded body that then has at least two s
Gruber Udo
Heine Michael
Kienzle Andreas
Kelly Cynthia H.
Mayback Gregory L.
SGL Carbon AG
Thompson Camie S.
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