Processing of ceramic matrix composites by pulsed-CVI and related techniques

P-CVD/CVI is used to densify model pores and to fabricate Nicalon/SiC microcomposites with pyrocarbon or (PyC-SiC)(n) multilayered interphases. The gaseous precursors are hydrocarbons (CH4 or C3H8) for pyrocarbon and CH3SiCl3-H-2 for SiC. The best densification conditions for 60; 120 and 320 mu m model pores, by pyrocarbon, are T = 900-1000 degrees C; P-2 = 1-3 kPa and t(R) = a few s. Even under such conditions, a thickness gradient is always present along the pore axis. Filling ratios as high as 90% are observed for the largest pores. Smooth or rough laminar pyrocarbon is deposited depending on the value of t(R) and hence the maturation of the gas phase. Multilayered (PyC-SiC), interphases (with n = 10-30 ; e(PyC) = 3-50 nm and e (SiC) = 10 or 30 nm) act as mechanical fuses and are more resistant to oxidation than pyrocarbon interphase. P-CVD/CVI can be used to elaborate highly engineered new ceramics.