Room- and high-temperature thermal conductivity of silicon carbide fiber-reinforced silicon carbide composites with oxide sintering additives

Green sheets of SiC containing Al2O3-Y2O3-CaO sintering additives prepared by the doctor-blade method and polycarbosilane-impregnated 2D woven Hi-Nicalon cloths with BN-coating were used for the fabrication of SiC fiber-reinforced SiC composite by hot-pressing. Thermal conductivity of the composite was measured between room temperature and 1000 degreesC. It increased with increasing bulk density, and was 5-11 W/m (.) K at room temperature. The thermal conductivity of the composites showed a maximum at approximately 500 degreesC or slightly increased with test temperature up to 1000 degreesC. The composite fabricated in this study showed relatively low thermal conductivity in spite of low porosity. The reasons for the low thermal conductivity could be attributed to the SiC matrix consisting of fine SiC grains, the phase transformation of 3C-SiC to 4H-SiC, and the low thermal conductivity grain-boundary phases, in addition to the large amount of SiC fibers with low thermal conductivity.