Influence of transformation toughening mechanisms of Zirconia based materials on the tribological performance under high mechanical contact loads and water lubrication

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Zirconia based materials are often used because of their combination of excellent wear resistance, high strength and toughness. Strength and toughness of zirconia are outstanding mechanical properties which make it the current standard ceramic material for pumps and seals. For these reasons, zirconia materials are often the first choice in applications with high mechanical loadings. In wet lubricated systems, however, the issue of low-temperature degradation during wear processes has to be investigated and become controllable in order to ensure a successful application over long periods of time. Thus, the proposed project aims for a basic clarification of a) mechanisms, kinetics and process parameters and b) the establishment of procedures to test degradation in situ aiming at the running-in phase of degradation for tribological development with respect to the interaction of degradation and wear.Model materials based on Y-doped tetragonal zirconia polycrystals (Y-TZP) and a composite material containing alumina (alumina toughened zirconia, ATZ) will be used to investigate the surficial phase transformation from tetragonal to monoclinic in wet lubricated systems as a function of environmental parameters (aqueous lubrication at temperatures between 20° and 90°C), loading conditions (speed, load, geometry) and time of treatment. The extent of trans-formation in amount and distribution is then correlated with microstructural changes (crack growth, residual stresses, and defects), resulting changes in mechanical properties (hardness, effective elasticity, toughness) and wear properties (friction, mass loss). An X-ray diffraction based in situ test and calibration procedure for the evaluation of critical conditions will be developed.