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

The no. of cycles to failure of plasma sprayed thermal barrier coatings during thermal shock expts. gives an indication of the performance in a real environment. We have subjected 0.3 mm thick ZrO2-8 wt.% Y2O3 TBC's to a local thermal shock load where the max. surface temp. was 1300 DegC and 1400 DegC. The spot size of the flame was about 15 mm. During the cycles, the temp. drop over the specimen thickness and the temp. profile on the back side of the substrate were measured. The no. of cycles to failure and the type of failure appeared to be dependent on the max. surface temp. of the coating. After failure, a phase anal. was performed. In addn., the residual stress profile in the topcoat after 200 cycles with Tsurf = 1300 DegC was detd. It was concluded that at 1300 DegC bond-coat oxidn. is the main cause of failure, while at 1400 DegC topcoat degrdn. leads to failure