Delamination-indicating thermal barrier coatings using YSZ:Eu sublayers

Nondestructive diagnostic tools that can reliably assess thermal barrier coating (TBC) delamination are needed to provide protection against premature TBC failure as well as to reduce the costs associated with unnecessary TBC replacement. A coating design for a TBC that is self-indicating for delamination has been successfully implemented by incorporating a europium-doped yttria-stabilized zirconia (YSZ) luminescent sublayer beneath the overlying undoped YSZ TBC. It was demonstrated that incorporation of the europium-doped YSZ layer could be achieved without disrupting TBC columnar growth by using multiple ingot electron beam physical vapor deposition. Both scanning luminescence mapping as well as luminescence imaging revealed greatly enhanced detected luminescence from scratch-induced delaminated regions. This enhanced detected luminescence arises due to high internal reflectivity of both excitation and emission wavelengths at the interface between the luminescent sublayer and the delamination crack. In particular, imaging of the enhanced luminescence associated with TBC delamination was fast and simple to implement, therefore showing great promise as a practical tool for inspecting for TBC delamination.