FEATURE / NEXT GENERATION CMC STRUCTURES Figure 11. EWCVD fabrication rig mid-process in fabricating a homogenous joining sample. important step forward in bringing monolith and composite ceramics to the same level of utility and consideration in manufacturing that metal and plastic/polymer-based enjoy presently, in part because of the capabilities that have been historically developed to link simpler constructed shapes from these materials into larger, more complex components. A homogenous joint combining silicon carbide fiber reinforced-silicon carbide matrix components with only SiC used in the welding materials is a significant advancement over the decades-long history of trying to join ceramics together without including non-ceramic materials. An important feature of EWCVD is the fact that the formation of the composite shell or weld is low cost because of the simplicity of the materials and process used. A number of wire wrap materials have been used to hold the non-woven SiC veil in place on a substrate, such as molybdenum and tungsten. Examples of lap joint samples prepared with the non-woven LCVD SiC fiber veil are shown in Figure 10. The non-woven veil offers up easily accessible porosity for the precursor gases to penetrate, avoiding impenetrable pockets that cannot be filled. During the matrix formation step, the nonwoven veil is heated uniformly because of the close contact with the wire wrap, preventing the setup of temperature gradients in the veil which results in uneven deposition of the matrix. Finally, compared to the weeks required for analogous CVI processing of ceramic composite components, EWCVD-based joining can be completed on the order of a couple of days. The processing rig is shown in Figure 11 during a fabrication run of a joining sample. This rig is used for both interphase deposition of a carbon 24 | SAMPE JOURNAL | MAY JUNE 2023 Figure 12. In-process SiC homogenous joining sample. Figure 13. As-produced welded component. coating on the LCVD SiC fiber veil and subsequent formation of the SiC matrix, accomplished by controlling the gas precursor environment to deliver the right combination of element chemistry. Process parameters such as input power to the www. sampe.orghttp://www.sampe.org