Delayed Fracture Behavior of Ceramics Under Tensile Loading at Elevated Temperatures

Abstract

This paper describes the delayed fracture behavior under tensile loading at elevated temperatures of three engineering ceramics: silicon nitride, silicon carbide and alumina/silicon carbide nanocomposites. There are two regions in the delayed-fracture mechanism map of silicon nitride; slow crack growth and creep damage rupture. The creep lives, which are mostly governed by facet-sized cavity formation, reasonably follow the Monkman-Grant relation. Silicon carbide, which generally does not contain glassy phase at grain boundaries, shows excellent creep resistance even at very high temperatures. The creep lives are well described by a diffusive crack growth model. Creep resistance of alumina/silicon carbide nanocomposite is markedly improved compared with that of alumina with an equivalent grain size, due to pinning effect of intergranular silicon carbide particles. The interface between the intergranular particles and the alumina matrix is much stronger than the alumina/alumina interface. This rigid bonding causes the inhibition of vacancy nucleation and annihilation at the interface, which results in threshold stress of creep.