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Presentation RSE 15002883

Thermophysical, microstructural characterisation and non destructive control of TBCs by photothermal and thermographic techniques


PACRIM 11th Pacific Rim Conference of Ceramic Societies 30-4, Agosto- Settembre-2015.

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F. Cernuschi (RSE SpA)

GRID RESILIENCE 2015 - Security and vulnerabilities of the electrical system

Thermal Barrier Coatings (TBC) are widely used to protect gas turbines hot parts from combustion gases.

Ceramic TBCs are widely used for protecting hot path components of gas turbines from combustion gases. The metallic substrate temperature can be significantly reduced depending on the thickness and on the specific properties of the thermal barrier coatings. In particular, thermal conductivity of TBCs is significantly affected by the specific microstructure of the top ceramic layer. Furthermore, during engine operation, owing to several high temperature cycle-dependent phenomena taking place, cracks close to the bondcoat-TBC interface nucleate and propagate up to final TBC spallation. From several years, photothermal and thermographic techniques have been successfully used to perform the thermo-physical characterisation of TBC and the non-destructive assessment of TBC integrity along with the operation In this work an overview of the following topics object of research at RSE will be given: Description of a thermographic technique able to measure the through-the-thickness and the in-plane thermal diffusivity of TBCs samples of different microstructure and aging conditions. A theoretical and experimental analysis of real capabilities of infrared techniques to estimate the porosity content of porous ceramic materials such as thermal barrier coatings (TBCs). Description of application of a potentially non destructive photothermal technique able to estimate some APS TBCs effective microstructural parameters by studying thermal diffusivity variations when pores are filled with different gases at different pressures. Description of a method, based on the evaluation of the TBC thermal diffusivity evolution during ageing compared to the as sprayed value, for the semi-quantitative estimation of the interface cracked fraction between the bondcoat and TBC within coupons subjected to thermal cycling. Description of the apparent thermal effusivity approach successfully applied to automatically distinguish between delamination and overthickness of TBCs samples and components.

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