Optimizing substrate and intermediate layers geometry to reduce internal thermal stresses and prevent surface crack formation in 2-D multilayered ceramic coatings

In order to avoid the formation of normal cracks in the external layer of multilayered ceramic coatings during cooling, determination of the residual thermal stress field is essential. Concerning the effect of the intermediate layers (transition zone) on a possible reduction of stress in the external layer, it has been shown that in the case of a symmetrical (or constrained in-plane strain) system, reduction only occurs over a critical substrate thickness. In order to investigate the effect of the substrate geometry, the residual thermal stress field has also been determined in other configurations such as an asymmetrical arrangement (one side coating) allowing bending and a concentric-cylinder structure. In these last two configurations, a strong stress reduction is obtained. For practical applications such as gas turbine ceramic components, these results may provide guidelines for an optimum design of the geometry of substrate and intermediate layers of multilayered ceramic coatings.