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Determining the effect of cycling on EB-PVD ceramic thermal barrier coatings of V94.3A2 First Stage Blades by the Use of Non-Destructive PLPS (Photoluminescence Spectroscopy) Technique

pubblicazioni - Articolo

Determining the effect of cycling on EB-PVD ceramic thermal barrier coatings of V94.3A2 First Stage Blades by the Use of Non-Destructive PLPS (Photoluminescence Spectroscopy) Technique

coatings of V94.3A2 First Stage Blades by the Use of Non-Destructive PLPS (Photoluminescence Spectroscopy) Technique Claudia Rinaldi*, Letizia De Maria*, Marco Mandelli** International Conference on Cyclic Operation of Power Plants London, 27-28 September 2007 *CESI RICERCA **PROING ITALIA In this paper the results are presented of analyses performed on some ex-service first stage blades, coming from plants operated with different operating conditions (base load and cyclic operation). Both NDTs and degradation models were used to quantify the influence of cycling. A recently developed portable PLPS device /1/ was applied for in shop measurements on components both before and after service operation; the residual stress level was determined at the BC/TBC interface where TGO (Thermally Grown Oxide) forms. The different degradation level of the interface was evaluated at several positions. The actual local effectiveness of film cooling could be evidenced. The TGO stress values measured by PLPS were used to estimate the spent life fraction, extending to components a literature correlation found on specimens /2/. Moreover some simplified models of TBC life evolution were implemented in a self made life prediction code for coatings with TBC. Using this code the mean local temperature was calculated through the inverse problem solution (IPS) method, starting from the depleted zone width of the metallic bond coat measured by metallography on blade sections or with the Frequency Scanning Eddy Current non destructive Technique /3,4/. Agreement was found between the mean local operating temperature estimated by the IPS routine of the life prediction software and the interface degradation detected by PLPS. Data collected on components at different positions were used to evaluate the local spent life fraction of TBC. Differences in TBC damage levels could be quantified and different values of residual life were estimated at equivalent positions on different components coming from base load and cyclic operation. An actual influence of cycling could be evidenced and quantified.

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