Surface treatment methods for mitigation of hydrothermal ageing of zirconia

Hydrothermal ageing of zirconia ceramics (tetragonal-to monoclinic phase transformation in the presence of humidity) is highly sensitive to the surface characteristics. Thus chemical modifications of the surfaces over a few microns may be a good way to mitigate ageing without affecting bulk mechanical properties. Here, the efficiency of different post-sintering thermal treatments in powder beds of different compositions to prevent or slow down hydrothermal ageing of 3Y-TZP is tested. The microstructure, ageing kinetics at different temperatures and mechanical properties of the treated samples are then evaluated. Treatments with 12Ce-TZP proved to be the most efficient to limit ageing at 134 degrees C while keeping good mechanical properties. However, this is accompanied by a decrease of the activation energy of ageing, thus by an acceleration of ageing at lower temperature. These results also show that the activation energy of ageing is material-dependant, thus should be ascertained for every developed zirconia-based ceramic.