In situ observations of stress-induced phase transformations in ZrO2-containing ceramics

In situ straining experiments were performed in a high-voltage electron microscope fitted with a double-tilting straining stage. The stress-induced tetragonal (t)-to monoclinic-(m) transformation was studied for t-ZrO2 inclusion confined in different ceramic matrices (Al2O3 spinel, cubic (c)-ZrO2) and for fine-grained t-ZrO2 poly-crystals (TZPs). Crack propagation could easily be observed, during which t-ZrO2 inclusions close to the crack tip transformed to m symmetry. The sizes and shapes of the transformation zones were evaluated for several transformation-toughened ceramics and are discussed with regard to their mechanical properties