The Relationship between Cyclic Fatigue Properties and Microstructures of Sintered Silicon Nitride Ceramics

Abstract

The present study deals with the relationship between the microstructures and the fatigue failure mechanisms in five different kinds of sintered silicon nitride ceramics. Static fatigue test and cyclic fatigue test were conducted with a stress ratio (R) condition of 0.1 using flex specimens at room temperature, as a means to determine the effects of microstructures on crack propagation. Also, the accelerative effects upon the propagation velocity of fatigue cracking in cyclic loading conditions were discussed quantitatively using the estimation method applied to the empirical equation for subcritical crack growth.The results indicated that the accelerative effects on propagation velocity under cyclic fatigue conditions were observable in samples in which the matrix was composed of microcrystalline grains of the sintered silicon nitride ceramics, but not in those with a matrix composed of amorphous materials. Thus, under cyclic loading, the fatigue crack propagation was found to be governed by the microstructure of the sample, in particular by the matrix filling the gaps between the coarse grains.