Crack Resistance and Fatigue of Transforming Ceramics: I, Materials in the ZrO2–Y2O3–Al2O3 System

Crack resistance characteristics and fatigue properties have been studied in four types of Y₂O₃–TZP ceramics including one containing Al₂O₃. The largely linear-elastic behavior connected with the very small transformation zone (<5 μm) explains the absence of any resistance-curve behavior and the flaw-controlled strength. The crack resistance shows high sensitivity to environment-induced subcritical crack growth. This influence is also operative in both types of fatigue experiments, i.e., under static and cyclic stresses, leading to reduced fatigue thresholds compared with K _IC. While for static conditions a benefit is observed from enhanced t-m ZrO₂ transformation, cyclic stresses provoke an additional fatigue effect. However, if the cyclic stresses are restricted to subthreshold values, cyclic stress-induced effects in the process zone provide an improvement of the materials being visible as a strengthening effect.