Transformation Toughening of Ceramics

Ceramic materials can be considerably toughened by utilizing the phase transformation of Zr02 particles. The transformation is nucleation-controlled and invariably stress-assisted. Three main toughening mechanisms are operative: stress-induced transformation, microcracking and crack deflection. Some toughened ceramics with low critical transformational stress “exhibit transformation plasticity and memory effects analogous to martensitic metal alloys. Micro- structural features of the three Zr02 toughened ceramic (ZTC) groups are presented: Partially — stabilized Zr02 (PSZ), tetragonal Zr02 polycrystals (TZP) and dispersion -toughened ceramics, e.g. ZT-AI2O3, ZT-mullite, etc. The mechanical properties of some ZTC are compared with predicted values. Since ZTC generally exhibit a disappointing high-temperature behavior, some strategies are outlined to overcome the characteristic deficiencies.