Toughening in ZrO_2-Based Materials

Fracture toughening processes in transformation toughened zirconia and related systems are reviewed. The main toughening derives from the martensitic transformation of tetragonal ZrO_2 particles to their monoclinic form ahead of a crack as analyzed by thermodynamic and continuum approaches. The implications for crack-length dependent fracture resistance based upon the toughening models are included. Additional toughening contributions are evaluated for microcracking and crack deflection processes using recent models. Systems where transformation toughening occurs are summerized, including materials which are surface-strengthened through the tetragonal-monoclinic transformation. The effects of temperature and environment on mechanical behavior are also considered.