Oxidation Resistance of Multilayer SiC for Space Vehicle Thermal Protection Systems

The oxidation resistances of different kinds of SiC-based laminates are compared. The materials under investigation are produced by tape casting of green ceramic sheets, followed by stacking of the sheets in a multilayer structure and laminate consolidation by de-binding and sintering. Three kinds of specimens are tested: multilayer SiC with fully dense layers, multilayer SiC integrating porous layers and multilayer composites made by stacking SiC/Cf composite layers. Two kinds of chopped carbon fibres (polyamide coated and uncoated) are used for the manufacture of the composite sheets. The oxidation behaviour is investigated by simultaneous TGA–DTA–MS analysis. Specimens are also submitted to a long-term oxidation treatment (30 h at 1 600 °C in flowing air) and their microstructure and mechanical behaviour compared before and after oxidation. This assessment shows that the integration of porous or composite layers in the multilayer architecture does not worsen the oxidation resistance. In every case the formation of a surface passivating layer prevents major degradation phenomena, so that only small changes in the mechanical features are found after oxidation.