Stress-Biased Anisotropic Microcracking in Zirconia Polycrystals

Anisotropic elastic response of microcracked bodies has been studied using transformation-toughened Mg-PSZ and Ce-TZP as model materials. These zirconias have been previously deformed in triaxial compression to effect various extents of phase transformation. Microcracks were found to align with the compression axis and their normalized density increases linearly with the extent of transformation plasticity. The measured elastic constants are anisotropic and well described by an elasticity theory. An additional anomalous elastic anisotropy was also found in Ce-TZP due to a transformation texture of both the remaining tetragonal phase and the newly formed monoclinic phase. The terminal crack density ω= Na ³, where N is the number of cracks per unit volume and a is the crack radius, reaches 0.05 in Mg-PSZ and 0.1 in Ce-TZP at the completion of transformation plasticity.