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pubblicazioni - Presentazione

Non destructive techniques for TBC life time assessment: Raman and Impedance spectroscopies

pubblicazioni - Presentazione

Non destructive techniques for TBC life time assessment: Raman and Impedance spectroscopies

Thermal Barrier Coatings (TBCs), consisting of a CoNiCrAlY bond coat made by LPPS technique and yttria-partially-stabilized-zirconia top coat with different porosity values produced by air plasma spray (APS). The non-destructive evaluation of TBC residual life in service is a challenge in the field of IGT maintenance. This paper presents two different approach to this problem using two non-destructive techniques: Raman Spectroscopy and Electric Impedance Spectroscopy. TBC samples have been tested to their thermal fatigue resistance limit by furnace cycling tests (FCT) The TBC systems have been cycled for different times in the range of as-coated to the failure limit. Raman Spectroscopy and EIS analysis was performed onto samples cycled for different percentage of estimated life. TBC Residual Stresses by Raman Spectroscopy analysis has been correlated with the residual life time and with the failure mode of the system under thermo-mechanical load. The impedance values decrease as the residual life decrease. A sharp impedance decrease and a different electrochemical behavior are recorded after the 70% of the estimated coating life. Raman Spectroscopy in combination with EIS could be used method to follow the TBC damaging and to evaluate the approach of the coating failure.

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