ABSTRACT
The fabrication and testing of SiC/SiC composites prepared by polymer infiltration and pyrolysis with a liquid, hyperbranched, allyl-substituted hydridopolycarbosilane (AHPCS) is described. This now commercially available polymer is used as both the matrix source and as a component in a fiber coating procedure. In addition to the infiltration of ceramic fiber preforms, it can be mixed with appropriate particulate reinforcents and molded into complex shapes. It undergoes crosslinking at ca. 300 °C and pyrolyzes to a near-stoichiometric SiC at 1000 °C. Six-ten infiltration/thermosetting/-pyrolysis cycles are used to obtain high final density composites for structural applications whereas three to four cycles provides porous materials suitable for use as filters. This polymer is also used, along with a C-precursor, to coat SiC fiber (Sylramic™) cloth. The resultant, two-phase, SiC/C material resists oxidation at 1000 °C in air and serves as an effective interphase in SiCf/SiCm composites even after exposure of the composites to air at 800 °C for > 5 days. The results of mechanical property measurements and microstructural studies carried out on both the C-coated Nicalon- and SiC/C-coated Sylramic-reinforced composites are presented.
