Joining of SiC/SiCf ceramic matrix composites for fusion reactor blanket applications

Joining SiC‐Based Ceramics and Composites with Preceramic Polymers

“…This indicates the formation of a strong adhesive bond between the substrate and the preceramic-derived ceramic material as well as the presence of a limited amount of residual stresses. However, in the case of the SiC/SiC f ceramic composite, the shear strength for the joint was not satisfactory, being on the average below 4 MPa [11]. The low strength was attributed to the presence of defects in the joining layer arising from shrinkage and densification of the preceramic polymer, concentrated within the non-flat areas of the composite surface.…”

“…The low strength was attributed to the presence of defects in the joining layer arising from shrinkage and densification of the preceramic polymer, concentrated within the non-flat areas of the composite surface. 2D and 3D composites, because of their different surface morphology, gave different results, with a lower strength for the samples possessing the most strongly textured surface (3D) [11]. The introduction of filler powders increased the strength and somewhat reduced the scattering of the data, due to the great decrease of shrinkage during pyrolysis, and the effective reduction defects in the layer.…”

“…Generally speaking, diffusion bonding requires elevated temperatures (not compatible with the retention of fiber strength in composite materials) or pressures, while active metal brazing tends to create complex reaction layers which sometimes exhibit poor thermo-mechanical properties. The use of preceramic polymers for joining SiC-based ceramics has been proposed in the recent literature [4][5][6][7][8][9][10][11][12][13]. Indeed, the use of preceramic polymers for joining offers a number of attractive features, such as easy application, low processing temperatures and possibility to tailor the joint composition by adding suitable fillers to the preceramic precursor, but nevertheless several issues remain to be addressed and some specific problems still need to be solved.…”

“…Thus the fibers were not exposed and did not participate to the joint formation. The real area of contact (flat zones) is smaller than the nominal one, typically of the order of 60 to 80% for the 3D composite specimens [9,11]. The preceramic polymers used in the joining experiments were: a methylhydroxyl-siloxane (SR350, General Electric Silicone Products Div., Waterford, NY) and two polycarbosilanes (PCS, Dow Corning X9-6348, and allylhydridopolycarbosilane (AHPCS, Starfire Systems, Watervliet, NY).…”

“…The pyrolysis cycle (heating and cooling rate, maximum temperature, dwelling time) were varied in order to assess the influence of the processing parameters on the strength and quality of the joints. The experimental details for the morphological, microstructural, compositional and mechanical analyses performed can be found elsewhere [5,9,10,11,13].…”