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

Thermal barrier coatings, used extensively on hot section gas turbine engin e components, weaken and spall after repeated thermal exposure during norma l engine operation. A new technique has been developed, involving the use o f vacuum impregnation of the porous ceramic with a mixture of epoxy and flu orescent dye (rhodamine-B) and the ASTM C 633-79 direct pull test, to prese rve 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. Imag e processing is used to quantify the area fraction of debonding. For the el ectron beam physical vapor deposited yttria-stabilized zirconia coating eva luated, a local area fraction of debonding of up to 20 % was observed at 80 % of spallation life.