Controlled experiments and a corresponding analytical model were developed to investigate the reasons for crack initiation in multilayer ceramic thermal barrier coatings. The experiments and model determined that surface cracks form as a result of tensile stresses created following stress relaxation in the ceramic at steady-state high temperatures (about 900°C–1100°C). Interface cracks generated by out-of-plane stresses are affected by the presence of these surface cracks and thermal transients and, possibly, edge effects.

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