Weibull characterization of the flexural strength of hydrothermally degraded 3Y-TZP zirconia

The flexural strength of 3% mol yttria-stabilized tetragonal polycrystalline zirconia (3Y-TZP) with a ~0.30 m grain size was studied under 4-point bending test. The material was evaluated both as received and after water vapour exposure for long times of 100hr and 200hr at 131oC in autoclave. Results were systematically analyzed by Weibull statistics and fractography. It was found that the mean flexural strength and Weibull modulus change from 960MPa and m=10.9 in the as received condition to 916MPa (m=19.5) and 860MPa (m=19.8) for 100 and 200 hours ageing, respectively. This increase in m can be explained by a change in the origin of fracture from natural flaws in the original material to original defects in the degraded surface layer which extend under loading to a depth equal to its thickness. This layer can be clearly appreciated during fractographic analysis after long degradation times. In the present case the thickness of the degraded layer was on average equal to 8.5 m after 100 hours of hydrothermal exposure.