How Surface Cooling Rate Affects the TBCs’ Spallation in Flame Thermal Shock Testing

When testing the thermal cyclic resistance of thermal barrier coatings (TBCs), the controlling of the surface temperature of the materials in the whole process, including heating up, temperature holding, and cooling, is extremely important since only in that way are the testing results indicative and applicable for life prediction of the coatings in real components. In this paper, the temperature at the surface of plasma sprayed TBCs (APS and PS-PVD) was well controlled with feedback of a double color infrared thermometer. As the cooling causes the main damage in the TBCs, different cooling rate was applied with recording the temperature changes at the front (coating surface) and back (superalloy substrate) sides of the samples. Higher cooling rate caused faster coating spallation. The columnar PS-PVD TBCs showed higher thermal shock resistance but the bulk APS TBCs had better thermal resistance. The failure mechanism of the TBCs was analyzed with study of the cross sectional microstructure.