Effect of the composition and sintering process on mechanical properties and residual stresses in zirconia–alumina composites

Samples of zirconia-toughened alumina (ZTA) with small amounts of chromia and magnetoplumbite-type crystalline phase (CeMgAl11O19) have been prepared and processed under different conditions. Mechanical properties like hardness and fracture toughness were examined as a function of different parameters. As an example, fracture toughness was increased by the chromia addition, whereas platelets reinforcement addition suppressed the tetragonal zirconia (t-zirconia)–monoclinic zirconia (m-zirconia) transformation. In addition, transformability of the tetragonal zirconia and the residual stress in the alumina phase were examined by Raman and fluorescence piezo-spectroscopy, respectively. In particular, the extent to which t-zirconia transforms to m-zirconia was determined by Raman spectroscopy after Vickers indentation and the transformability was correlated to the fracture toughness. It was demonstrated that the monoclinic content and the toughness were correlated linearly and experimental results were compared with models already available for zirconia-based materials. On the other hand, residual stresses originated by transformation toughening mechanism were correlated to the transformability of the tetragonal phase.