PROTECTION AGAINST OXIDATION OF C SIC COMPOSITES - OXIDATION BEHAVIOROF CVD TIB2 COATED SUBSTRATES/

Titanium diboride coatings (20 or 30 mum thick), deposited by hydrogen reduction of TiCl4 and BCl3, are protecting C/SiC substrates against oxidation up to 1100-degrees-C. The oxidation of TiB2 leads to the for mation of a protective low viscosity B2O3 glass filling the cracks of the primary CVD-SiC oxygen barrier. Above this temperature, the rapid consumption of the B2O3 glass by vaporization limits the duration of t he protection system. A comprehensive description of the oxidation mec hanism, based on a complementary experimental study of B2O3 evaporatio n, is presented.