Effects of fiber volume fraction on the densification and mechanical properties of unidirectional SiCf/SiC-matrix composites

Unidirectional SiCf/SiC-matrix composites with a pyrocarbon interface were prepared by hot-pressing SiC nano-powder via a liquid phase of sintering additives under high temperature (1900 °C) and applied pressure (20 MPa). The SiC reinforcing fiber volume fraction of the composites varied from 0 to 78 vol% and was found to have significant effects on densification and mechanical properties, where changes in failure mode, proportional limit stress, ultimate strength, and elastic modulus were observed. The mechanical properties were significantly enhanced with an increase in the fiber volume fraction until a moderately high fiber content was obtained, after which the ultimate strength of the composite degraded. These observations were related to the open porosity within the fiber bundles. Further, fiber strength was affected by fiber damage caused by contact with the surrounding matrix due to poor densification of the SiC nano-powder.