A process that involves reaction forming has been devised to enable the joining of high-temperature-resistant structural parts made of SiC-based materials. These materials include SiC-based ceramics and composites reinforced by fibers that are made of various component materials and are woven, wound, or otherwise arranged in various configurations. The technique can be used to join simply shaped parts to make complexly shaped structures, and to repair such parts and structures.
The process begins with the application of a carbonaceous mixture to the joint regions between parts. The mixture is cured at a temperature between 90 and 110 °C. The joints are then locally infiltrated with molten silicon or with alloy(s) of silicon and refractory metal(s). The molten silicon or alloy reacts with the carbon in the joint to form silicon carbide with amounts of silicon and refractory disilicide phases that can be tailored by choice of the compositions of the reactants. Consequently, the process results in joints with tailorable microstructures and thus tailorable thermomechanical properties. The properties of the joints can be tailored to approximate closely those of the joined parts.
The figure shows some examples of SiC-based ceramic and fiber-reinforced composite parts that were joined by use of this process. In mechanical tests, the joints on these parts were found to retain their strength at temperatures from ambient up to 1,370 °C. The test temperature of 1,370 °C is above the maximum to which the parts are expected to be exposed in use.
This work was done by Mrityunjay Singh of NYMA, Inc., for Lewis Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Materials category, or circle no. 157 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).
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