Piezo-spectroscopic technique for assessing thermal shock cracks in alumina-zirconia composites ,

The commonly used procedure for assessing thermal shock resistance of ceramics is based on the measurement of bending strength retained from bars quenched at different temperatures and necessitates the use of a large number of test pieces. In order to overcome this inconvenience and identify a method that can be used to analyze directly a component, an attempt to use a piezospectroscopic technique to identify the critical temperature was carried out. The method is based on the concept that in presence of cracks, residual stresses that can be present in a ceramic material should be released. To verify this hypothesis a ceramic composite [namely alumina-zirconia (3YTZP)] that exhibits internal residual stresses at room temperature was prepared. By means of alumina fluorescence peak shift we collected maps of residual stress in alumina shocked at different ?T and with different cracks density. The variation of the stress fields associated with different ?T were compared with the results obtained with the standardized procedure. A critical evaluation of the new method is proposed.