An affordable and flexible method of joining silicon-carbide-
(SiC-) based monolithic ceramics and fiber-reinforced ceramic
matrix composites (CMC's) is being developed at the NASA Lewis
Research Center. This technology will make it possible for ceramic
and CMC components to be used for high-temperature applications
in aeropropulsion, launch, and onboard space propulsion systems.
Our goal is to develop a joining approach that can be scaled up
to provide joints between SiC-based CMC or monolithic ceramic
components or subcomponents.
In this joining process, which is based on the SiC reaction processing
method, carbonaceous mixtures are applied to the joint area and
subsequently infiltrated with molten silicon. The molten silicon
reacts with carbon to form SiC joints that contain a controllable
amount of silicon. This approach can be controlled via modification
of the reactive constituents to yield joints with tailored microstructures
and properties. The approach should be affordable because precision
joint machining is unnecessary, the reactive constituents are
inexpensive, and a pressureless melt infiltration process is used
to introduce the molten silicon. The flexibility of the process
makes it applicable to the joining of any SiC-based monolithic
or composite material, and the ready availability of the required
processing equipment to commercial materials suppliers facilitates
technology transfer.
Thus far, several types of commercially available and NASA-processed SiC ceramics--including reaction bonded, reaction formed, and pressureless sintered SiC--have been joined. Joints having strengths that equaled or exceeded the strength of the base material were formed in reaction-bonded SiC. In addition, the ability to join CMC cylinders to CMC panels by using this reaction-joining approach has been demonstrated, as shown in the photo.
Previous articleLast updated April 30, 1997
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