Wear mechanisms associated with the lubrication of zirconia ceramics in various aqueous solutions

摘要

The wear and friction behaviours of self-mated zirconia ceramics were investigated with sliding tests in various aqueous solutions using a reciprocating ball-on-flat testing geometry. The surface charge on the native surfaces and the wear debris were "controlled" by varying the pH of the aqueous solution over a wide range, i.e., between 1 and 13. The aim of this investigation was to determine the wear mechanisms via analyses of the wear debris using SEM, XRD and TEM. Significantly different properties were observed, depending on the testing conditions in the different aqueous solutions; and the nature of the wear debris and the native surfaces was also found to depend on the testing conditions. Regions with high and low levels of wear and friction were detected. The wear was found to vary by as much as an order of magnitude with the change in pH, and under the same conditions the friction was observed to change by a factor of two. In the first region, i.e., under very acidic conditions, chemical dissolution was the predominant effect, resulting in low wear and low friction. At higher pH values, more complex processes consisting of a hydrothermal transformation causing bulk zirconia fracture and the formation of tribochemically assisted wear-debris layers, which subsequently spalied, resulted in rough surfaces with very high wear and high friction. Furthermore, the electrochemical effects in this region caused a wear peak to appear at the isoelectric point.