Weibull strength statistics of hydrothermally aged 3Â mol% yttria-stabilised tetragonal zirconia

The effect of hydrothermal degradation on the flexural strength and on the fracture statistics of 3 mol% yttria-stabilized tetragonal zirconia (3Y-TZP) has been investigated. To do so, a large number (>30) of specimens were tested in four-point bending test after exposure to water vapour at 134 °C and 2 bar pressure for different periods of time up to 200 h. The decay in mechanical strength with hydrothermal degradation material was analysed by Weibull statistics, and a strong increase in the Weibull modulus was observed (from 12 to 20). These results are discussed in terms of the thickness of the surface degraded layer, the size of natural defects in the specimens and the fracture toughness of both the tetragonal and monoclinic phases. The increase in Weibull modulus is associated with a change in the control of fracture from natural defects to the thickness of the surface degraded layer.