Cyclic contact loading of Y-TZP ceramics with spherical SSiC shape under ambient air and water-lubricated conditions

The influence of phase transformation toughening (PTT) on the surface damage behavior of 3. mol% yttria stabilized zirconia (Y-TZP) was studied by cyclic contact loading with spherical SiC indenter. Cyclic loadings were applied under ambient air and water lubrication, respectively, on two Y-TZPs differing in grain size and thus transformability of the tetragonal phase. In both materials, radial fretting and tribo-chemical wear were initiated at local spots within the micro-slip zone. Transformation into the monoclinic phase was found to occur adjacent to these surface damages dependent on the transformability of the plate material. While growth of damage incidences during repeated loading may be supported by transformation-induced micro-cracking the initiation of fatigue-induced cracking is suppressed by PTT and was therefore only observed in the fine grained ceramic. Generally, water acts as a lubricant and decreases the propagation of surface damages by reducing the s urface shear stresses.