Ceramic composite materials having tailored physical properties

Details Ceramic composite materials having tailored physical properties Ceramic composite materials having tailored physical properties

1998-10-14

2001-04-03

Copenheaver, Blaine (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Noninterengaged fiber-containing paper-free web or sheet...

C428S294100, C428S297400, C428S298700, C428S299100, C428S300100

Reexamination Certificate

active

06210786

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to structural and mechanical parts formed from fiber-reinforced ceramic matrix composite (FRCMC) materials, and more particularly, to such parts having specific types of fibers and filler materials incorporated therein so as to tailor the ductility, hardness and coefficient of friction exhibited by the parts.
BACKGROUND OF THE INVENTION
Fiber reinforced ceramic matrix composite (FRCMC) materials have recently been employed to make structural components for aircraft. Specifically, these components have been used as so called “hot structures”, i.e. portions of the aircraft which must withstand high temperatures. FRCMC parts have fibers of various types and lengths disposed throughout a ceramic matrix formed from a pre-ceramic resin. Such parts have advantages over those formed of organic composite materials. For example, organic composites would tend to degrade in high temperature environments such as described above. While organic composites will burn readily, FRCMC, being a ceramic, withstands heat that can destroy even metals. A FRCMC material can withstand continuous temperatures up to about 1000° F., cyclical temperatures up to about 2000° F., and short-term exposure to temperatures up to about 3500° F. FRCMC structures also have advantages over those made from monolithic ceramic materials. Although monolithic ceramic structures can withstand high temperatures, they tend to be porous, delicate, and brittle. These parts are easily broken or cracked when impacted, or otherwise subjected to even moderate forces. Parts made from FRCMC materials, on the other hand, exhibit an increased ductility. Ductility for the purposes of the present invention is defined as the amount of strain a sample of the FRCMC material can withstand before fracturing. Increasing the ductility of a part makes it less susceptible to the fracturing associated with monolithic ceramic parts.
FRCMC materials have in the past been generally restricted to structural components designed to withstand high temperature environments. Other than its inherent heat resistance, no other significant demand is made on the parts employed in these types of applications. However, FRCMC materials could be useful in many other applications where certain additional physical characteristics would be required. For example, FRCMC materials could be employed in mechanical parts which are intended to be in sliding contact with other parts. In such a case it would be desirable that the FRCMC material exhibit high ductility and erosion resistance, and a low coefficient of friction. In other applications, such as in the friction components of brakes and clutches, the same erosion resistance would be desired, but the FRCMC material would have to exhibit a high coefficient of friction to prevent slipping. In the case of structural components, a FRCMC part may not only be required to withstand high temperatures, but also abrasive environments. This calls for a FRCMC material which is hard enough to survive in these abrasive environments.
Accordingly, there is a need for parts made of FRCMC materials that exhibit a desired ductility, hardness (i.e., erosion resistance) and/or coefficient of friction required for a particular application.
It is therefore an object of the present invention to provide FRCMC parts which exhibit a desired degree of ductility.
It is another object of the present invention to provide FRCMC parts which exhibit a desired degree of hardness, or a desired coefficient of friction, or both.
These and other objects of the present invention will become apparent throughout the description thereof which now follows.
SUMMARY OF THE INVENTION
The above-described objects of the invention are realized by the tailoring of physical properties or characteristics exhibited by a fiber-reinforced ceramic matrix composite (FRCMC) structure. In general, FRCMC material includes a polymer-derived ceramic resin in its ceramic state, fibers, and possibly filler materials. The pre-ceramic resin used to form the FRCMC material can be any commercially available polymer-derived ceramic precursor resin, such as AlliedSignal's BLACKGLAS™, Dupont Lanxide's Ceraset™, Dow Chemical's SYLRAMIC™ or Applied Polymerics' CO-2 resin, and the fibers are preferably at least one of alumina, Nextel 312, Nextel 440, Nextel 510, Nextel 550, silicon nitride, silicon carbide, HPZ, graphite, carbon, and peat. The fibers are also preferably coated with an interface material taking the form of at least one 0.1-0.5 micron thick layer of at least one of carbon, silicon nitride, silicon carbide, silicon carboxide, or boron nitride. Filler materials can be incorporated into the composite to produce certain characteristics desired to be exhibited by the FRCMC material.
The aforementioned tailoring of characteristics exhibited by a FRCMC structure includes incorporating fibers into the composite to produce the desired degree of ductility necessary to ensure the survival of the FRCMC structure. Additionally, the hardness and the coefficient of friction exhibited can be tailored by incorporating filler material into the composite to produce the desired degree of these characteristics. In both cases, the degree to which these respective characteristics are exhibited varies with the percent by volume of fibers and filler materials incorporated into the structure. Additionally, the degree to which these respective characteristics are exhibited varies with the form of fibers used and with the type of filler material employed. Therefore, the tailoring of the characteristics exhibited by a FRCMC structure specifically involves selecting the quantity and form of the fibers that will produce the desired ductility, and selecting the amount and types of filler material that will produce the desired hardness and/or coefficient of friction in the FRCMC material.
The fibers in general will preferably make up about 15 to 55 percent of the volume of the FRCMC structure depending on the degree of ductility desired. In regards to the form of the fibers, a selection can be made between a continuous or a non-continuous fiber configuration. A continuous fiber configuration corresponds to woven fiber systems where the individual fibers typically run the entire length of the FRCMC structure, whereas non-continuous fiber configurations are associated with loose or chopped fibers which often terminate within the structure itself. Fibers in a continuous fiber configuration can produce a higher degree of ductility than will a non-continuous fiber configuration.
The filler materials, if used, preferably take the form of powders having particle sizes within a range of about 1 to 60 microns, and will make up from about 10 percent to about 60 percent of the volume of the FRCMC structure. Filler materials such as alumina, mullite, titania, and silicon carbide will increase both the hardness and the coefficient of friction compared to a structure lacking these materials. Filler materials such as graphite, silicon nitride and iron, and silica will decrease both the hardness and coefficient of friction exhibited by the FRCMC structure. Finally, filler materials such as silicon nitride, boron nitride, and boron carbide will increase the hardness while decreasing the coefficient of friction exhibited by the structure.
An example of a FRCMC structure with tailored characteristics is one having enhanced hardness and erosion resistance characteristics, such as might be employed in an abrasive environment. Such a structure is made up of a polymer-derived ceramic resin as earlier exemplified in its ceramic form, fibers in sufficient quantities to produce a desired degree of ductility in the structure, and filler material in sufficient quantities to produce the desired degree of hardness in the structure. Preferably, the fibers are also coated with one of the aforementioned interface materials to increase the ductility of the structure even further.
The fibers incorporated in the erosion resistant FRCMC structure may be either in a continuous or n

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