Fracture performance and crack growth prediction of SPS TBCs in isothermal experiments by crack numbering density

This study examined the application of crack numerical density theory (CND) to determine the damage state of a thermal barrier coating (TBC) produced using the suspension plasma spray (SPS) technique. A TBC consisting of a partially stabilized zirconia topcoat was deposited upon an APS NiCoCrAl bondcoat and INCONEL 625 substrate. The TBC was exposed to an isothermal temperature of 1080 degrees C for a duration of up to 1300 h with specimens removed for examination at, 400 h, 800 h and 1300 h. Material properties after each exposure were determined and utilized to fit a CND model to predict the crack distribution within the topcoat following isothermal exposure. Probabilities of cracks developing within the topcoat that can bridge asperities (0.01% at 400 h, 2% at 800 h, and 11% at 1300 h) were determined indicating that CND may be a useful tool for predicting lifetimes of SPS-TBCs.