FATIGUE FRACTURE-BEHAVIOR OF OXIDE CERAMICS IN WATER

The characteristics of static or cyclic fatigue fracture of two ceramics (alumina, Al2O3, and partially stabilized zirconia, ZrO2) under tensile loading have been investigated in high purity water at room temperature. The time to fracture in static and cyclic fatigue tests in water was shorter than that in air. In addition, it decreased markedly with increasing K(I) or DELTAK(I). From the observations of fracture surfaces for static and cyclic fatigue by scanning electron microscopy, it was shown that the fracture surface was mixed intergranular and transgranular cracking in Al2O3 and intergranular cracking in ZrO2. The fracture behavior under cyclic loading revealed the occurrence of time-dependent fracture in Al2O3 and cyclic-dependent fracture in ZrO2. The reason why the fracture time is decreased by cyclic fatigue in ZrO2 is considered to result from the promotion of interaction between fatigue crack and microstructure, such as microcracking and phase transformation in the process zone. and from the activation of a hydration reaction at the crack tip.