Effect of local thermal shock load on plasma sprayed thermal barrier coatings

Abstract

The number of cycles to failure of plasma sprayed thermal barrier coatings (TBCs) during thermal shockexperiments gives an indication of their performance in a real environment. The authors have subjected 0·3 mm thick ZrO₂–8Y₂O₃ TBCs to a local thermal shock load with maximum surface temperatureof 1300 and 1400°C. The diameter of the flame was about 15 mm. During cycling, the temperature drop through the specimen thickness and the temperatureprofile of the back of the substrate were measured. The number of cycles to failure and the type of failure appeared to be dependent on the maximum surface temperature of the coating. After failure, a phase analysis was performed. In addition, the residual stress profile of the top coat was determined after 200 cycles with T_surf = 1300°C. It is concluded that at 1300°C bond coat oxidation is the main cause of failure, while at 1400°C top coatdegradation leads to failure.