2-DIMENSIONAL SIC/SIC COMPOSITES PROCESSED ACCORDING TO THE ISOBARIC ISOTHERMAL CHEMICAL VAPOR INFILTRATION GAS-PHASE ROUTE

Chemical vapor infiltration (CVI) is a process according to which a ceramic material is deposited from a gaseous precursor in the open pores of a heated substrate. It has been used to elaborate ceramic matrix composites, starting from porous fiber preforms. SiC/SiC composites consist of an SiC CVI-matrix reinforced with Si-C-O ex-polycarbosilane yarn fibers. These composites exhibit non-brittle mechanical behavior in tension loading when a thin layer of a compliant interphase material (turbostratic pyrocarbon or hex-BN) with a low shear failure stress is deposited onto the fibers prior to infiltration of the SiC-matrix. When exposed to oxidizing atmospheres, SiC/C/SiC composites are self healing if their carbon-interphase is thin enough and the temperature is high. Their oxidation resistance can be improved by replacing the vulnerable carbon-interphase by a BN-interphase (low temperature exposures) and/or adding a glass-former coating on the external surface of the composites.