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 degrees C and 1200 degrees C by four-point bending tests. Cyclic fatigue lives were equal to static ones at both RT and 1000 degrees C, but higher than static ones at 1200 degrees C. Crack propagation was a mixture of intergranular and transgranular modes at RT and 1000 degrees C. However, fracture at 1200 degrees 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. (C) 1998 Elsevier Science S.A. All rights reserved.