STATIC AND CYCLIC FATIGUE IN SIC WHISKER-REINFORCED SILICON-NITRIDE COMPOSITE

Static and cyclic fatigue tests of 20 vol% SiC whisker-reinforced Si3N 4 matrix composite processed by gas pressure sintering were carried ou t 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 degre es C. Crack propagation was a mixture of intergranular and transgranul ar 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 u nder cyclic loading retards the cavity growth and therefore leads to l onger fatigue life than under static loading. (C) 1998 Elsevier Scienc e S.A. All rights reserved.