THERMAL FRACTURE OF MULTILAYER CERAMIC THERMAL BARRIER COATINGS

Controlled experiments and a corresponding analytical model,cere devel oped to investigate the reasons for crack initiation in multilayer cer amic thermal barrier coatings. The experiments and model determined th at surface cracks form as a result of tensile stresses created followi ng stress relaxation in the ceramic at steady-state high temperatures (about 900 degrees C-1100 degrees C). Interface cracks generated by ou t-of-plane stresses are affected by the presence of these surface crac ks and thermal transients and, possibly, edge effects.