Thermal fracture of interfaces in precracked thermal barrier coatings

Thermal barrier coatings (TBCs) make it possible to operate gas turbines, aircraft engines and diesel engines at higher temperatures, thus enabling significant improvements in the performance of these systems. In this paper, the effect of introducing surface cracks into plasma sprayed TBCs was studied. The resistance of these precracked coatings to interfacial fracture was determined both experimentally and analytically. In the experiments performed, beam-shaped specimens, with crack densities varying from 0 to 42 cracks inch−1, were subjected to a high heat flux generated by a 1.5 kW CO2 laser for a time interval of 4 s followed by natural convection cooling. In each case, the surface temperature which resulted in interface crack initiation was determined. Similarly, the final interfacial crack length corresponding to the different crack densities was measured as a function of maximum surface temperature. In all cases, it was shown that increasing crack density resulted in decreased interfacial cracking at the end of the thermal shock procedure. A numerical model of the experiment was developed using the finite element method and it was used to study the effect of the laser heating process on an interface crack in a precracked TBC system. The analytical results confirmed and explained the experimentally observed behavior.