INITIATION OF SURFACE CRACKS IN MULTILAYER CERAMIC THERMAL BARRIER COATINGS UNDER THERMAL LOADS

The initiation of surface cracks in thick ceramic thermal barrier coat ings systems was studied by using controlled experiments and the corre sponding analysis. The experimental boundary conditions consisted of a concentrated heat flux at the surface of the coating and water coolin g at the bottom of the substrate. The results showed that tensile stre sses were formed at the surface during cooling following stress relaxa tion during steady state heating. A parametric study showing that a lo w Young's modulus and a low coefficient of thermal expansion for the c oating would reduce these tensile stresses and increase its durability .