Crack Driving Forces of Atmospheric Plasma-Sprayed Thermal Barrier Coatings

Abstract

High-temperature operation service conditions can be used to evaluate the durability of Atmospheric Plasma-Sprayed Thermal Barrier Coating systems (APS-TBCs). To evaluate the durability of TBCs within their life span, two different thermal cycling testing results, i.e., isothermal furnace cycling and burner rig cycling tests, are utilized to numerically investigate possible crack driving forces that might lead to the failure of TBCs. Although there are many studies on failure and life prediction, there is still a lack of quantitative evaluation and comparison on the crack driving forces under these two different thermal cycling schemes. In this paper, by using modified analytical models, strain energy release rates (ERRs) are estimated and compared between these two testing approaches using experimental data. A new residual stress model was developed to study the position where the maximum residual stress occurs due to coefficient of thermal expansion (CTE) mismatch at different thermally grown oxide (TGO) thicknesses. The main crack driving forces are identified for two types of thermal cycling. A possible cracking route is found based on the calculated equivalent ERRs with respect to distance from the interface between the topcoat (TC)/TGO layers. The relationship between crack driving force of isothermal furnace and burner cycling tests is also elaborated.