Strength Characteristics of Transformation‐Toughened Zirconia

Mechanisms of failure in a transformation‐toughened MgO‐partially‐stabiltzed ZrO 2 are identified using in situ observations. The observations are related to measured stress‐strain curves, strengths under various loading conditions, strength degradation from surface damage, and comparative strengths and toughnesses of toughened and overaged materials. Both reversible and irreversible tetragonal‐to‐monoclinic transformations, as well as microcracking, are associated with nonlinear stress‐strain curves. The influence of this nonlinear response on stresses produced by flexural loading is evaluated. Failure is preceded by stable growth of microcracks, resulting in R ‐curve behavior and damage‐tolerant strength characteristics. The implications of R ‐curve response for strengthening and toughening characteristics are discussed.