Development of life prediction methodology for thermal barrier coatings based on nondestructive piezo-spectroscopy photoluminescence measurements

Durability of Thermal barrier coatings (TBCs) exposed to hot combustion environment is a major concern to the aerospace industry. Typical failure mechanism of electron beam physical vapor deposited (EBPVD) TBCs is separation or spallation of the ceramic top coat at the thermally grown oxide (TGO) layer. TBC spallation occurs when the residual stresses at the TBC-TGO bond coat approaches zero. The objective of the investigation was to develop an analytical approach to determine the remaining service life of TBC coated components using nondestructive photo-luminescence piezo-spectroscopy (PLPS) measurements. EBPVD coated samples were exposed to both isothermal and thermal cycling at three temperatures (1093°C, 1149°C, and 1204°C). Samples were removed at periodic intervals up to failure. The PLPS technique was used to measure the residual stresses at the interface of TBC-TGO. A model was developed for predicting the remaining life of TBC system based on the correlation between the residual stresses at the TBC-TGO interface and the shift in the TGO luminescence frequency. Remaining life prediction of the model was validated on samples thermally cycled at 1121°C. The predicted values of remaining life were compared with experimental data.