High-temperature fatigue in advanced ceramics

In recent years, improved processing has produced a new generation of advanced--also described as engineering of fine--ceramics in which the internal defect size if both smaller and more uniform. Mechanical properties are better, and there has been a surge in research interest to demonstrate the value of ceramics as structural materials and thus exploit their traditional superior properties. Popular among this new generation of materials are silicon carbide, silicon nitride and alumina. Enormous potential exists in high-temperature applications, such as gas turbines (blades and disks) and petroleum-based engines (piston rings). In some cases, the limit of the realistic capacity of metallic materials has been reached, and ceramics offer the only route for further progress. To develop design strategies based upon structural integrity, the answers to two questions are essential: what is the size of the defect that will cause fracture under the envisaged loading conditions, and how quickly will any intrinsic defect grow to attain this critical dimension?