Yttrium Silicate Coatings for Oxidation Protection of Carbon–Silicon Carbide Composites

Abstract

Yttrium silicate (Y 2 SiO 5 ) coatings complement SiC coatings for protecting ceramic multilayer composite materials based on carbon‐fiber‐reinforced SiC composites (C‐SiC). Thick (100 μm), dense Y 2 SiO 5 coatings were prepared by dip coating, using concentrated aqueous slips. The resulting phases were studied by taking into account the simultaneous presence of oxide and non‐oxide materials, which affected the chemical stability of the coatings. Thick, mechanically stable coatings were obtained by sintering in carbon crucibles and a SiC bed in an argon‐flow furnace. Pure Y 2 SiO 5 coatings completely separated from the SiC substrates. A high percentage of Y 2 Si 2 O 7 was necessary to fit the thermal expansion coefficients and ensure the stability of the coatings. Oxidation resistance of the coated substrates was investigated by isothermal and stepwise oxidation tests.