Delamination of Electron-Beam Physical-Vapor Deposition Thermal Barrier Coatings using Luminescent Layers

摘要

Thermal Barrier Coatings (TBCs) protect and insulate the superalloy parts in hot sections of gas turbine engines and are used to achieve higher turbine inlet temperatures, resulting in an increase in engine efficiency and consequently a lowering of NOx emissions and fuel consumption. Such performance is only possible if the integrity of the TBC under aggressive thermo-mechanical environments is ensured. Delamination is common but characterization methods to assess the severity of the damage are lacking. In this work, a Kubelka-Munk model was constructed to quantify numerically the luminescence contrast between intact and delaminated coating areas. This method relies on the drastic change in reflectivity at the interface between the top coat and the bond coat when a delamination forms. Two distinct TBC configurations containing an erbium-doped yttria-stabilized zirconia (YSZ:Er) layer for delamination sensing were used to validate this model. An artificially-induced delamination was successfully tracked on each sample configuration by measuring the luminescence contrast at different emission lines of erbium at around 545, 562, 655 and 680 nm to further validate modeling predictions as well as to evaluate the effect of wavelength-dependent scattering of the TBC with delamination detection capabilities. Luminescence-based methods for delamination detection combined with quantification models can provide accurate diagnosis with potential for the enhanced monitoring of high-temperature coatings throughout their lifetime.