Toughening Mechanisms for Monolithic Ceramics

The last decade has seen a dramatic improvement in the mechanical properties of structural ceramics. Strengths in excess of 2GPa and fracture toughness values higher than 1KJm-2 are now possible. These improved properties are possible because of the availability of highly sinterable powders coupled with hot isostatic pressing and the incorporation of new toughening mechanisms such as transformation toughening and fiber and whisker reinforcement. Means of combining more than one mechanism in a specific microstructure are also being developed. The primary role of the most effective troughening mechanisms is to reduce the crack tip stress intensity factor by 'crack tip shielding'. In this manuscript the various mechanisms for toughening are outlined along with examples of materials systems exhibiting this behaviour.