Influence of the Si3N4 Microstructure on Its R-Curve and Fatigue Behavior

The R-curve and fatigue behavior of a silicon nitride with large, highly elongated grains were compared to those of a silicon nitride with smaller, more equiaxed grains. The former was found to have higher toughness and a slightly rising R-curve which enhanced fatigue resistance, while the latter had constant toughness with crack length. The R-curve was attributed to crack deflection and grain pull-out. The microstructure did not influence the dynamic fatigue properties of the two ceramics, as both had good resistance to dynamic fatigue. The cyclic fatigue resistance of the large-grained Si3N4, however, was surprisingly low.