Fabrication Of SiCf/SiC Composites And Their Chemical Compatibility With Melt LiPb

SiCf/SiC composites are promising candidate structural and functional materials for fusion reactor applications. The Chinese Dual Functional Lithium Lead Test Blanket Module system uses SiCf/SiC composites as the Flow Channel Insert. In this paper, three-dimensional four-directional (3D4d) and 2.5 dimensional (2.5D) woven SiCf/SiC composites were fabricated through different process using homemade fibers and preceramic. The properties of the composites were characterized and the chemical compatibility of melt LiPb with SiCf/SiC at 700℃was studied primarily.The density of 3D4d SiCf/SiC composites fabricated through preceramic polymer impregnate and pyrolysis process (PIP) was 1.97g·cm^-3, the bend strength and modulus were 323.10MPa and 87.03GPa, the fracture toughness was 11.22 MPa·m^1/2 , the sheer strength was 49.23 MPa, and the thermal conductivity was 1.14 W·m^-1·K^-1. After 30 hours of chemical vapor deposition (CVD) coating, the density of the composites was 2.05g·cm^-3, the bend strength and modulus were 353.01MPa and 94.43GPa, the fracture toughness was 12.18 MPa·m^1/2, the sheer strength was 50.33 MPa and the thermal conductivity was 1.57 W·m^-1·K^-1.2.5D SiCf/SiC composites were fabricated through PIP process. The fiber/matrix bonding of the composites was weak so the composites showed tough fracture behavior. But the matrix was not densified and could not transfer the load effectively, so the strength and modulus of the composites were low. After different time of CVD SiC coating, the composites were densified and the strength and modulus were improved evidently. But the interfacial bonding got stronger, so the composites turned to brittle fracture behavior. Compared to the composites directly coated, the composites fabricated through CVD+PIP densification processes showed similar density, lower mechanical properties higher cost. Therefore, the better combination was to have a direct CVD coating after PIP cycles.3D4d and 2.5D SiCf/SiC composites were exposed to static LiPb at 700℃for 500 hours, the mechanical properties were degraded badly. 2.5D SiCf/SiC composites were totally broken and the mechanical properties of 3D4d SiCf/SiC composites indicated a severe reduction. The liquid metal reacted with the amorphous SiC: SiC+Ni→NixSiy+C, which resulted in the corrosion of the fibers and matrix. Weave structure determined the porous structures, thus affected the penetration of liquid metal.3D4d composites had pores of smaller size and less connectivity, so they had better compatibility with LiPb than 2.5D composites. The coating was compatible with LiPb, which delayed the reaction between the liquid and the composites, so the composites with CVD coating were better in appearance and properties after corrosion than those without coating.