Fatigue Behavior and Fracture Toughness of Mullite Ceramics Containing ZrO2 at 1200°C

The static and dynamic fatigues of 72 and 74mass% Al2O3 mullite ceramics containing 10vol% ZrO2 (72A-10Z, 74A-10Z) were measured at 1200°C, and the fracture toughness was evaluated from the size of a slow crack growth (SCG) region. The crack growth parameters N obtained by the static fatigue technique were 15 for 72A-10Z and 37 for 74A-10Z, On the other hand, the N values obtained by the dynamic fatigue technique were 23 for 72A-10Z and 30 for 74A-10Z. Fracture toughness (KIC), obtained by the controlled surface flaw (CSF) method after the static fatigue measurement, was 2.5MPa⋅m1/2 for 72A-10Z or 1.6MPa⋅m1/2 for 74A-10Z, and was negligibly affected by the addition of ZrO2. The fracture toughness of 72A-10Z obtained after the dynamic fatigue measurement varied considerably with stressing rate. The fracture toughness obtained through static and dynamic fatigue measurements showed the rising R-curve behavior. Enhanced fracture, toughness and R-curve behavior in 72A-10Z were attributed to the fracture of rodlike crystals and/or the viscoelastic flow of the glassy phase in the grain boundary.