Structural and Mechanical Property Changes in Toughened Magnesia‐Partially‐Stabilized Zirconia at Low Temperatures

The mechanical properties of high‐toughness magnesia‐partially‐stabilized zirconia were found to be dramatically altered by a single cooling cycle between room temperature and − 196°C. Raman spectroscopy and X‐ray diffraction were used to correlate the changes in mechanical properties with structural changes that occur at temperatures below ∼− 100°C. Most of the tetragonal precipitates that are responsible for toughening transformed to an orthorhombic phase with unit‐cell volume intermediate between those of the tetragonal and monoclinic phases. The orthorhombic phase was stable with heating to 300°C, but it transformed back to the tetragonal structure when heated to 400°C. Surprisingly, the orthorhombic phase was not readily transformable by stress, with the consequence that, after the cooling cycle, most of the high‐toughness properties of the original tetragonal‐containing material were lost.