Crack Growth in Thermal Barrier Coating Subjected to Thermal Cycling under Temperature Gradient

Thermal cycling tests are carried out under a temperature gradient using specimens of thermal barrier coating (TBC). Vertical cracks in the topcoat grow in the direction of the coating thickness, and transverse cracks in the topcoat, which can lead to delamination, grow in the vicinity of the interface with the bondcoat. At a temperature of 1223 K at the substrate surface, with a heat flux of 1.39 MW/m 2 , remarkable growth of transverse cracks is observed, whereas the growth is slower at lower temperatures and heat flux conditions. The transverse crack growth is evaluated using the energy release rate based on Hutchinson’s method. Further, the energy release rate is calculated for a TBC on an in-service blade of an F-class gas turbine. For this, the results from a numerical simulation for the temperature distribution of the blade are used. The criteria for crack growth that can lead to TBC delamination are discussed.