Damage evolution in an electron beam physical vapor deposited thermal barrier coating as a function of cycle temperature and time

Failure of thermal barrier coatings (TBCs) deposited on a single-crystal superalloy with a grit-blasted platinum modified nickel aluminide [β-(Ni, Pt) Al] bond coat has been studied as a function of thermal cycling temperature and time. One-hour cyclic furnace tests were conducted at 1100 °C, 1121 °C and 1151 °C, and 24-h tests were run at 1121 °C. It was found that all the samples tested in the 1-h cycle failed in the TBC, near the TBC/TGO interface, due to progressive cracking beginning at ∼20% life fraction. In contrast, the 24-h cyclic test samples failed at the TGO/bond coat interface. Thus, a life prediction for this TBC will ultimately require the use of two independent damage mechanisms and failure will be predicted on the basis of whichever occurs first during the TBC cyclic life. A single-valued relation was found between the rumpling amplitudes and the oxide thickness, independent of temperature and cycle time, consistent with oxidation being rate controlling.