Masayuki Kondo, Yuzuru Ogura and Tatsuo Morimoto
Advanced Technology Research Center, Mitsubishi Heavy Industries, Ltd. Yokohama 236-8515As an oxidation protection system for carbon/carbon composites beyond 1973 K, the authors have proposed a Y2SiO5 oxidation protection coating system, which is a multilayer coating system composed of a Y2SiO5 outer layer and a SiC inner layer. This work evaluated the Y2SiO5 coating in oxidation protection properties and emissivity properties. For oxidation protection properties, an erosion test was performed at 2073 K for 50 min in low oxygen pressure and high velocity gas flow (Mach 3, Ar-20 vol%O2) by an arc wind tunnel, and isothermal oxidation tests were performed in Ar-0.2 vol%O2 with an Iridium-heater electric furnace. In the erosion test, the Y2SiO5 coating protected a carbon substrate from oxidation, and the inner SiC layer was oxidized in active oxidation. The Y2SiO5 layer adhered to the SiC layer after the erosion test. In the isothermal oxidation tests, the Y2SiO5 coating performed oxidation protection at 1973 K for more than 10 h, but, the adhesion of the Y2SiO5/SiC interface was degraded by the isothermal oxidation tests. Total emissivities of the Y2SiO5 coating was estimated to be 0.54 at 1973 K by spectrum emissivities of the Y2SiO5 coating from 700 to 2500 nm. Therefore, this work showed that the Y2SiO5 coating performs oxidation protection above 1973 K at low oxygen pressure, and that an improvement of the emissivity properties was required for re-entry applications. For the improvement of the emissivity properties, it was proposed to coat the Y2SiO5 layer with high-emissivity oxides which had a high melting point.
yttrium silicate, carbon/carbon composites, oxidation protection, silicon carbide, yttrium silicide, plasma spraying, arc wind tunnel, active oxidation, emissivity