Introduction

The interest in the mechanical behavior of ceramics is often related to their use as a structural material. Ceramics and other inorganic materials have been used as structural materials for millennia, but invariably as compressive members. Transformation toughening is based on the idea that a phase transformation can be stress induced in a material in such a way that it decreases the driving force that is acting to propagate the cracks that are present, or can form under stress, in the material. The retention of the high temperature tetragonal phase to room temperature is the key to the fabrication of transformation-toughened materials. It needs to be remembered that powder processing needs considerable attention in the production of the specific microstructures required in transformation-toughened ceramics. The transformation within the transformation zone tries to make the zone larger, but this is opposed by the surrounding untransformed material.