Erosion-indicating thermal barrier coatings using luminescent sublayers

A successful approach to producing thermal barrier coatings (TBCs) that are self-indicating for location and depth of erosion is presented. Erosion indication is demonstrated in electron-beam physical vapor-deposited (EB-PVD) TBCs consisting of 7 wt% yttria-stabilized zirconia (7YSZ) with europium-doped and terbium-doped sublayers. Multiple-ingot deposition was utilized to deposit doped layers with sharp boundaries in dopant concentration without disrupting the columnar growth that gives EB-PVD TBCs their desirable strain tolerance. TBC-coated specimens were subjected to alumina-particle-jet erosion, and the erosion depth was indicated under ultraviolet illumination by the luminescence associated with the sublayers exposed by erosion. Sufficiently distinct luminescent sublayer boundaries were retained to maintain an effective erosion-indicating capability even after annealing free-standing TBCs at 1400 degrees C for 100 h.