Microcracking Contributions to the Toughness of ZrO_2-Based Ceramics

Analyses are presented to evaluate two microcrack toughening situations in Zr_O2-based ceramics. The first analysis considers toughening due to stress-induced microcracking of residually strained monoclinic ZrO_2 particles. The second assesses microcracking that occurs as a consequence of the stress-induced tetragonal-monoclinic transformation. Both toughening mechanisms are characterized by a permanent dilatational strain and a modulus reduction; however, only the latter may result in a toughness enhancement or reduction. Conditions under which toughness enhancement and reduction are observed are established. The magnitudes of toughening increases from transformation-toughening and microcrack-toughening are also compared.