Effect of Microstructure on Cyclic Fatigue Properties of Al2O3 Ceramics and Al2O3 Composites

The cyclic fatigue properties of three kinds of toughened Al2O3 composites doped with SiC whisker, TiC and partially stabilized ZrO2 particle were compared with results of four kinds of Al2O3 ceramics with different purities. The effects of stress amplitude and initial crack size on fatigue properties were investigated by using polished and pre-cracked samples. Furthermore, the accelerated phenomena on initiation and propagatation velocities of fatigue crack under cyclic loading condition were quantitatively assessed by the estimatation method using an experimental relation based on subcritical crack growth velocity and static fatigue data. As results, in the case of polished sample, the accelerated effect on fatigue that 99.99% and 99% Al2O3 ceramics typically showed was restrained in Al2O3 composites. The cyclic fatigue properties of Al2O3 composites used in this paper can be successfully estimated under wider condition of stress application from the data on static fatigue than the case of Al2O3 ceramics. On the condition that a sample was pre-cracked by Knoop indenter, Al2O3 composites hindered the accelerated effect on fatigue crack propagation under cyclic loading as well. Especially, the cyclic fatigue data of pre-cracked ZrO2/Al2O3 composite agreed well with the estimated value from static fatigue properties.