Dynamic fatigue of a Si3N4+SiC nanocomposite at 1350°C

The dynamic fatigue strength of a hot pressed silicon nitride/silicon carbide nanocomposite and reference monolithic Si3N4 have been investigated in four-point bending at 1350°C in air using different loading rates from 0.01 to 1 mm min−1. The flexure strength significantly decreased with decreasing stress rate in both ceramics, however at all stress rates the strength of the composite was lower than that of the monolithic. The formation and growth of a stress-oxidation damage zone are primarily responsible for the strength degradation of the monolithic ceramic. In the composite intrinsic flaws were the main fracture origins, which extend by oxidation assisted slow crack growth and decrease the strength of the specimens significantly.