Evaluation of Applicability of LED Light Sources to Detection of Thermally Grown Oxide Layer in Thermal Barrier Coating for Gas Turbines

The applicability of LED light sources to detection of thermally grown oxide (TGO) layer in thermal barrier coating (TBC) for gas turbines was evaluated. A green LED of center wavelength 540 nm was found to be more efficient than a blue LED of center wavelength 460 nm to excite Cr3+ in the TGO layer. Using the green LED, photoluminescence was observed at 694 nm for TBC specimens heated at 1100°C. The dependence on the heating time was the same as the case of laser excitation. Using a green LED light source with higher power, photoluminescence was also observed for specimens heated at 1000°C. The results indicated that an inexpensive TGO detection system can be constructed using LED light sources.