Fatigue crack propagation in aluminum nitride ceramics under cyclic compression

Room temperature fatigue crack growth characteristics under cyclic compress ive loads were investigated in pure and 3 wt % yttria doped hot pressed alu minum nitride ceramics. A single edge-notch specimen geometry was used to i nduce a stable Mode I fatigue crack under cyclic compressive loads. The fat igue crack growth occurred in three stages, where the first stage is domina ted by microcrack nucleation, coalescence and slow growth within the notch root. During the second stage, the crack growth is accelerated and finally, the crack growth deceleration and arrest occurred in third stage. The fati gue crack growth occurred predominantly by intergranular fracture. Insights gained from the experimental results and microscopic observations are disc ussed. (C) 1999 Kluwer Academic Publishers.