Non-destructive evaluation of ceramic components for engines

Advanced ceramics have several advantages which make them important materials for structural applications: low density, high strength and hardness, low heat expansion and good heat conductivity combined with high thermal stability and oxidation resistivity. But there is one disadvantage that even at high temperatures advanced ceramics are brittle, what means that stress peaks at defects cannot be released by plastic flow and ductility. From the stress analytic and fracture mechanical point of view for design loads of some 100 MPa defects with lineare dimensions of 10-100 mym - at the surface still smaller ones - will cause failure. This makes a nondestructive quality control absolutely necessary. The full variety of NDT-techniques described in the different chapters has demonstrated their ability for quality control of advanced ceramics mostly in laboratory applications and in limited areas of applications. Only for high resolution X-ray testing in projection technique the state of the art of the equipments allows a direct application in practice. For ultrasonic testing as well as for photoacoustics and vibration analysis the appropriate equipment still is under development. (IZFP)