Crack Propagation Behavior in Gas Pressure Sintered Silicon Nitride

Abstract

The crack propagation behavior in gas pressure sintered Si₃N₄ was investigated under cyclic and static loading by 3-point bending for pre-cracked specimens by indentation on the center of the mirror finished tensile surfaces. Crack propagation occurred under cyclic loading with a maximum applied stress below the applied stress at which crack propagation stagnated under static loading, showing that crack propagation velocity under cyclic loading was higher than that under static loading. Although intergranular crack propagation with crack-bridging was observed in both cases under cyclic and static loading, crack-bridging, observed after static loading, was found to be fractured by the subsequent cyclic loading. It was thought that the crack shielding force by crack-bridging, which is effective for restraining crack propagation under static loading, was decreased by cyclic loading, resulting in faster crack propagation under cyclic loading than under static loading.