High temperature oxidation of two- and three-dimensional hafnium carbide and silicon carbide coatings

The difficulty in using C/C composites as structural components above 2000 °C in an oxidizing atmosphere is their poor lifetime. The solution proposed here consisted in combining two refractory carbides, hafnium and silicon carbides, in coating with a complex architecture, named a three dimensional coating, over a C/C substrate. Such a coating protects the C/C composite at 2000 °C under air. The oxidation of the coating leads to the formation of a SixOyHfz hafnium-containing silicate liquid, combined with HfO2(s). This liquid limits oxygen diffusion more than pure SiO2 does, so it is a better protection against oxidation. Furthermore, HfO2(s) acts as a frame holding SixOyHfz in place. From these results, an oxidation mechanism is proposed and discussed.