Stress rate dependence of fracture strength in pre-cracked zirconia ceramics

In this study, the fracture strength of three kinds of zirconia ceramics, 2Y-TZP, 8Y-FSZ and 9Mg-PSZ is investigated under vast range of stress rate (10−3–103 MPa s−1) by using indented rectangular samples. Compared with other ceramics like silicon nitride, the fracture strength of zirconia ceramics is found to be affected more by the environment, which causes a slow (or subcritical) crack growth (SCG) behavior. However, the strength degradation by SCG can be saved to some extent for 9Mg-PSZ and 2Y-TZP by the phase transformation triggered by the environmental factors like H2O and O2, or the well-known stress induced phase transformation. Furthermore, in TZP ceramics, benefiting from its specific anelastic behavior possibly caused by ferroelastic domain switching or grain reorientation, the fracture strength is greatly improved in lower stress rate region at 523 K, though a strength degradation at this temperature was stated in many past literatures.