Thermal shock and thermal cycling behavior of silicon nitride ceramics

In order to reproducibly characterize the thermal shock behavior of ceramic materials that are intended to be applied in stationary gas turbines, a fracture-mechanics-based test method is under development. The main feature of this technique is to generate a defined thermal gradient in a small sample by laser irradiation. The first application of this method to Si3N4 is presented. It is shown that figures-of-merit being typical for a material can be determined. In the case of cyclic severe stresses failure occurs after a relatively small number of cycles. This may be explained by a large subcritical crack growth rate under cyclic stresses. (orig.)