Adhesion strength of ceramic top coat in thermal barrier coatings subjected to thermal cycles: Effects of thermal cycle testing method and environment

This paper deals with the adhesion strength of ceramic top coat in thermal barrier coatings (TBCs) subjected to thermal cycles under several different test conditions. Here the TBC specimens consisting of 8% yttria stabilized zirconia, CoNiCrAlY alloy bond coat and Ni-base superalloy were prepared by plasma spraying. The isothermal exposure and the thermal cycles were applied to the TBC specimens by several conditions at high temperatures. A series of the test results clearly demonstrated that the adhesion strength of the top coat was significantly changed by the application of thermal cycles and by the isothermal exposure. It was also found that the thermal fatigue damage might be evolved depending on of the testing method by which the thermal cycles are applied. Some background of these findings were discussed, based on the measurements of elastic modulus, tensile strength, and thermal conductivity of the ceramic top coat, as well as both the thermally grown oxide at the top coat/bond coat interface and the residual stress in the TBC specimens.