Delamination-indicating of atmosphere-plasma-sprayed thermal barrier coating system using Eu³⁺ luminescence mapping

The strong scattering of the microstructures severely weakens light transmitted through the atmosphere-plasma-sprayed (APS) thermal barrier coating system (TBCs), which poses a great challenge to indicate APS TBCs delamination using optical inspection method. In this paper, to indicate the delamination in APS TBCs, an innovative method was proposed based on a luminescent sublayer that produces significantly greater emission intensity from delaminated regions of the TBCs. The top coat was prepared with a Eu³⁺-doped yttria-stabilized zirconia (YSZ:Eu³⁺) luminescent layer below an undoped YSZ layer. The delamination was prepared using a dissolved salt method. Specimens were vacuum-impregnated with mineral oil to improve the transparency of the coating, and thus to reduce the effects of pores and microcracks on luminescence signal. For specimens with a Eu³⁺-doped YSZ luminescent sublayer, luminescence intensity mapping showed excellent contrast between the delaminated region and the surrounding adherent region.