Abstract
The fracture and damage behaviour of high temperature materials can be modified by realizing well-defined property gradients. The damage characterization of thermal barrier coatings (TBCs) by means of laser irradiation shows that crack propagation perpendicular and parallel to the heated surface are the crucial phenomena. Crack propagation parallel to the surface leads to delamination and spalling. In terms of fracture mechanics, optimizing gradients means minimization of the ratio between the energy release rate G for delamination and its critical value G c . The aim is to allow maximum load at large TBC thickness. Two effects are discussed by means of an example. One is the reduction of G for stationary heat flow and the other one is the higher G c through a gradient towards a more ductile material. A method for measurement of G c for thin, brittle layers is presented. Cyclic surface heating by laser irradiation enables us to quantitatively evaluate the damage resistance of non-graded and graded TBCs.
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