Ambient and elevated temperature mechanical properties of hot-pressed fused silica matrix composite

The ambient and elevated temperature mechanical properties of two kinds of hot-pressed fused silica matrix composites, SiO2+5 vol.% Si3N4 and SiO2+5 vol.% Si3N4+ 10 vol.% Cf, were investigated. Si3N4 additions greatly enhanced the ambient strength and fracture toughness, while, further incorporation of chopped carbon fibers only but sharply increased the fracture toughness value from 1.22 to 2.4 MPa m1/2. The strength of the two composites synchronously exhibited anomalous gains at certain elevated temperature range especially from 1000 to 1200 °C, and reached their maximum values at 1000 °C, 168.9 and 130.6 MPa, which were 77.0 and 77.4% higher than their ambient strength, respectively. The two composites exhibited catastrophic fracture even at 1000 °C, but manifested prominent plastic deformation at 1200 °C and usually no fracture occurred during the strength test. Vickers’ indentation crack propagation behavior, combined with fractographs studies, suggested that toughening from carbon fiber was attributed primarily to the fiber bridging, pull-out and crack deflection.