OPTIMIZATION OF AN INTERPHASE THICKNESS IN HOT-PRESSED SiCf/SiC COMPOSITES

The effects of the thickness of PyC interphase on the properties of hot-pressed SiCf/SiC composites were investigated. Slurries of SiC nano-powders containing Al2O3/Y2O3/MgO sintering additives were infiltrated into the SiC fiber preform with various PyC thicknesses of 200-1000 nm. Densification behavior, microstructural evolution, and mechanical properties of the hot-pressed composites were evaluated. The hot-pressed composite revealed an optimum interphase thickness which was larger than the CVI composite. Density of the hot-pressed composites decreased as the PyC thickness increased. Decrease of the density with the PyC thickness was attributed to the limitation of the slurry infiltration within the SiC fiber bundles. The SiCf/SiC composites with the PyC thicknesses of 200 and 400 nm showed brittle fracture behaviors due to the elimination of the PyC interphase by the reaction between the oxide phases and PyC during fabrication. However, the composites with the PyC coating of more than 600 nm exhibited pseudo-ductile fracture behaviors with higher strengths.