Yttrium silicate coatings for oxidation protection of carbon-silicon carbide composites

Yttrium silicate (Y2SiO5) coatings complement SiC coatings for protecting c eramic multilayer composite materials based on carbon-fiber-reinforced SiC composites (C-SIC). Thick (100 pm), dense Y2SiO5 coatings were prepared by dip coating, using concentrated aqueous slips. The resulting phases were st udied by taking into account the simultaneous presence of oxide and non-oxi de materials, which affected the chemical stability of the coatings. Thick, mechanically stable coatings were obtained by sintering in carbon crucible s and a SiC bed in an argon-flow furnace. Pure Y2SiO5 coatings completely s eparated from the SIC substrates. A high percentage of Y2Si2O7 was necessar y to fit the thermal expansion coefficients and ensure the stability of the coatings. Oxidation resistance of the coated substrates was investigated b y isothermal and stepwise oxidation tests.