Assessment of damage accumulation in thermal barrier coatings using a fluorescent dye infiltration technique

Thermal barrier coatings, used extensively on hot section gas turbine engine components, weaken and spall after repeated thermal exposure during normal engine operation. A new technique has been developed, involving the use of vacuum impregnation of the porous ceramic with a mixture of epoxy and fluorescent dye (rhodamine-B) and the ASTM C 633-79 direct pull test, to preserve and reveal incipient damage and accumulated damage prior to spallation in thermal barrier coatings. Excellent definition of damage is provided by the dye in electron beam physical vapor deposited coatings, but the damage is more difficult to distinguish in the highly porous plasma coatings. Image processing is used to quantify the area fraction of debonding. For the electron beam physical vapor deposited yttria-stabilized zirconia coating evaluated, a local area fraction of debonding of up to 20 % was observed at 80 % of spallation life.