INITIATION OF SURFACE AND INTERFACE EDGE CRACKS IN FUNCTIONALLY GRADED CERAMIC THERMAL CARRIER COATINGS

The initiation of surface and interface edge cracks in functionally gr aded ceramic thermal barrier coatings resulting from the application o f a thermal load is studied. For a given specimen configuration, the s ingular behavior of the thermal stresses is analytically determined in terms of a singularity power beta and pseudo-stress intensity factors K-1 and K-2. Crack initiation at the surface at the interface is rela ted to the surface temperature and the temperature difference between the surface of the coating and the substrate. The experimental results are used to provide Weibull curves for the probability of survival of plasma sprayed mullite and CoCrAlY coating systems.