Sol-gel elaboration of porous oxide coatings as interphase in SiC/SiC ceramic matrix composites

Combinations of meso-, macro- and microporous coatings with a chemical composition of 90%Al2O3-10%SiO2 were elaborated on SiC Hi-Nicalon fibers using the sol-gel process. They were evaluated as porous interphase for the reinforcement of CMC. The mesoporous oxide, in contact with the fiber, allows cracks deviation whereas the macroporous one, in contact with the matrix, avoids the gaseous infiltration of the mesopores during the SiC CVD matrix process. It also prevents from oxygen diffusion during high temperature under air. The characterization of the composites was performed by SEM (scanning electron microscopy), TEM (transmission electron microscopy), X-ray diffraction, and EDS (energy dispersive spectrometry). TEM evidenced the porosity gradient as expected. A tensile test on the composites revealed brittle behavior (fracture) and no fiber debonding was observed.