Dynamic Fatigue Behavior of Ceramics at Elevated Temperatures

Abstract

The dynamic fatigue tests of nine structural ceramics were carried out at temperatures ranging from 800°C to 1500°C in vacuum. The same tests in air were conducted for two ceramics. In ceramics which has a glassy phase in grain boundaries, cracks propagate through grain boundaries due to softening of the glassy phase. A fatigue parameter of ceramics at elevated temperatures is degraded when MgO is used as a sintering additive. In reaction sintered Si₃N₄ and HP-SiC with B and C additives, a subcritical crack growth is not observed but the bending strength of HP-SiC is degraded due to the generation of pores by surface oxidation. It seems that life-time of HP-Si₃N₄ under the static load is predictable from its dynamic fatigue behaviour.