Microstructure and properties of porous SiC ceramics with AlN-RE2O3 (RE = Sc, Y, Lu) additives

The intrinsic microstructure and crystalline phases of porous SiC ceramics with 5 vol% AlN-RE2O3 (RE = Sc, Y, Lu) additives were characterized by high-resolution transmission microscopy with energy-dispersive spectroscopy and X-ray diffraction. The homophase (SiC/SiC) and heterophase (SiC/junction) boundaries were found to be clean; that is, amorphous films were not observed in the specimens. In addition, ScN, YN, and LuN were formed as secondary phases. The flexural strength and thermal conductivity of the ceramics were successfully tuned using different additive compositions. The flexural strength of the ceramics improved by a factor of -3, from 11.7 MPa for the specimen containing Y2O3 to 34.2 MPa for that containing Sc2O3, owing to the formation of a wide necking area between SiC grains. For the same reason, the thermal conductivity improved by -56%, from 9.2 W center dot m- 1 center dot K-1 for the specimen containing Lu2O3 to 14.4 W center dot m- 1 center dot K-1 for that containing Sc2O3.