The very scattered life times of thermal barrier coatings used on the first stage rotating blades of GTs used in power generation plants encourage the development of reliable non destructive techniques to reliably detect degradation before spalling. Among the optical non contact techniques Photo stimulated Luminescence PiezoSpectroscopy (PLPS) is promising as it lets to measure the residual compressive stress values of the thermally grown oxide (σTGO) at the interface between the BC and the ceramic top coat of EB-PVD thermal barriers. This paper underlines the potentiality of the photoluminescence piezospectroscopy as a diagnostic tool to assess the actual local film cooling efficiency on ex service blades with EB-PD TBCs. TGO stress values measured by PLPS (well related to the local degradation level of the interface, as observed on metallographic sections) result to be correlated with holes positions at all the different height of the blade examined. Moreover the reliability of the NDT evaluation is shown to increase significantly with an automatic PLPS instrumentation able to map σTGO in the regions of interest. The recorded large number of σTGO values suitably elaborated give a statistically significant evaluation of the degradation level reached by the TBC/BC interface, before spallation. A quantitative relationship between spent life fraction and σTGO formulated in the literature is here extended to ex-serviced blades to quantify the NDT result in terms of spent life fraction. These results are discussed in the light of T and spent life fraction estimates made with a simplified life model of TBC coatings.

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