Boron Nitride Interphase in Ceramic-Matrix Composites |
| |
| Authors: | Roger Naslain Olivier Dugne Alain Guette Jean Sevely Christian Robin Brosse Jean-Philippe Rocher Jacques Cotteret |
| |
| Affiliation: | Laboratoire des Composites Thermostructuraux (UMR 47 CNRS-SEP-UB1), 33600 Pessac, France;CEMES-LOE, Centre National de la Recherche Scientifique, 31055 Toulouse, France;SociétéEuropéenne de Propulsion, BP 37, 33165 Saint Médard-en-Jalles, France |
| |
| Abstract: | A BN interphase has been deposited, by isothermal/isobaric chemical vapor infiltration (ICVI) from BF3─NH3, within a preform made from ex-polycarbosilane (ex-PCS) fibers, at about 1000°C. In a second step, the BN-treated preform was densified with SiC deposited from CH3SiCl3─H2 at about the same temperature. From a thermodynamic standpoint, ex-PCS fibers could be regarded as unreactive vs the BF3─NH3 gas phase assuming they are coated with a thin layer of carbon or/and silica. The as-deposited interphase consists of turbostratic BN (N/B < 1) containing oxygen. The SiC infiltration acts as an annealing treatment: (i) the BN interphase becomes almost stoichiometric and free of oxygen; (ii) the fibers undergo a decomposition process yielding a SiO2/C layer at the BN/fiber interface. The weaker link in the interfacial sequence seems to be the BN/SiO2 interface. Deflection of microcracks arising from the failure of the matrix takes place at (or nearby) that particular interface. |
| |
| Keywords: | composites chemical vapor infiltration boron nitride silicon carbide cracks |
|
|
