ABSTRACT
Surface flaws can be introduced in a ceramic as a result of high-temperature grain boundary grooving, post-fabrication machining operations or accidental damage to the surface during use, among others. The effect of temperature on the strength of a ceramic depends on many factors the most important of which is whether the atmosphere in which the testing is being carried out heals or exacerbates preexisting surface flaws. Transformation-toughened materials owe their very large toughness to stress-induced transformations of a metastable phase in the vicinity of a propagating crack. An ongoing theme in materials design, or so, has been to understand how nature designs tough materials and try to mimic it, an approach, not surprisingly, labeled biomimetics. In a hardness experiment, a small region in the ceramic is placed under high pressure by the indenter. Hardness and concomitant wear resistance are important attributes that render ceramics useful in many structural applications.
