Static and cyclic fatigue in SiC whisker-reinforced silicon nitride composite

Static and cyclic fatigue tests of 20 vol% SiC whisker-reinforced Si3N4 matrix composite processed by gas pressure sintering were carried out at room temperature (RT), 1000°C and 1200°C by four-point bending tests. Cyclic fatigue lives were equal to static ones at both RT and 1000°C, but higher than static ones at 1200°C. Crack propagation was a mixture of intergranular and transgranular modes at RT and 1000°C. However, fracture at 1200°C was characterized by a process of nucleation, growth and interlinkage of cavities in front of a major crack. The enhanced bridging stress under cyclic loading retards the cavity growth and therefore leads to longer fatigue life than under static loading.