Structural changes in ZrO2 ceramics during sliding under various environments

The wear mechanisms of self-coupled zirconia ceramics during sliding in aqueous solutions at various pH were investigated. The results show that the wear rate of zirconia in aqueous solutions is significantly higher than for the alumina under the same conditions and its dependence on the pH-controlled surface charge is much less pronounced than for alumina ceramics and may be explained to a significant degree by mechanisms associated with phase transformation. Analysis of the wear scars and wear debris revealed that the tribolayer formed during the wear process consists of agglomerates composed of a large number of particles that transformed to monoclinic phase during sliding as well as particles of cubic zirconia of size 3-5 nm precipitated from the matrix amorphous phase which formed during the sliding process. Hence, in contrast to alumina, where a protective hydroxide layer is formed and its behavior can be modified by the surface charge, the transformation of zirconia seems to be the wear determining mechanism, putting zirconia in the position of a material with a limited range of wear applications.