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Photothermal and thermographic techniques for ndt controla and thermophysical characterisation of TBC

pubblicazioni - Articolo

Photothermal and thermographic techniques for ndt controla and thermophysical characterisation of TBC

thermo physical characterisation of TBC Federico. Cernuschi*, Lorenzo Lorenzoni*,Davide Robba**, Sergio.Martinetti*** Paolo Bison***, Ermanno Grinzato*** Turbine Forum 2006 – Advanced Coating for high Temperatures Nizza, 26-28 Aprile 2006 *CESI RICERCA ** CESI SpA ***CNR–ITC PD The main problem encountered in in-field tests on Thermal Barrier Coatings (TBCs) deposited on gas turbine blades, is the difficulty to correctly interpret the experimental data. The coating thickness changes, which are not regarded as anomalies, are one of the most common sources of false alarms. They are very challenging to recognize because, unlike stains, eroded areas and optical property variations, they are not detectable in the visible band. Furthermore, their thermal signal is similar to the one produced by an adhesion defect. In this paper, a procedure to reliably discriminate thickness changes and real defects is proposed. The approach is based on the analysis of the apparent effusivity profile. Preliminary results are presented and discussed. Moreover, in order to prevent the spallation of TBC, it would be essential to monitor their degradation in terms of sintering kinetic. As sintering strongly affects also the thermal diffusivity of TBC, the idea is to measure the latter parameter to account for the former. The technique to measure thermal diffusivity using pulsed thermography is described, together with the model that leads to the identification of TBC diffusivity. Tests and results on specimens artificially aged are reported.

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