Piezo-spectroscopic analysis of the residual stresses in zirconia-toughened alumina ceramics: The influence of the tetragonal-to-monoclinic transformation

Samples of zirconia-toughened alumina (ZTA) with very small amounts of strontium hexaluminate have been prepared and processed under different conditions. The residual stress in the alumina phase has been examined by fluorescence piezo-spectroscopy. The extent to which tetragonal zirconia (t-zirconia) transforms to monoclinic zirconia (m-zirconia) has been determined by X-ray diffraction. It is demonstrated that the monoclinic content and the stress are correlated linearly, within the experimental error. The correlation has also been theoretically modelled using a stochastic description of the residual stress field. The model reproduces very well the dependence of the stress on the monoclinic content. Finally two strategies for the use of ZTA in room temperature applications are presented, based upon the experimental results: the first strategy entails the introduction of a controlled, superficial t-m transformation, whereas the second one consists in preserving the material untransformed prior to service.