Scheduled at:
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Tuesday, June 03, 2008, Auditorium 2 2:00 PM Gasturbines 3 Coatings for mobile and stationary turbines, protection against wear, high temperature corrosion and thermal stresses, clearance control coatings for a better efficiency
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Authors: |
Carlo Giolli* / Turbocoating SpA, Parma Andrea Scrivani / Turbocoating SpA, Italy Gabriele Rizzi/ Turbocoating SpA, Italy Francesca Borgioli/ Dipartimento di Ingegneria Civile, Università di Firenze, Italy Luca Lusvarghi/ Università degli Studi di Modena e Reggio Emilia, Italy Giovanni Bolelli/ Università degli Studi di Modena e Reggio Emilia, Italy
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Abstract: |
Failure Mechanism for Thermal Fatigue of Thermal Barrier Coating systems. C. Giollia,c, A. Scrivanic, G. Rizzic, F. Borgiolib, Giovanni Bolellid and Luca Lusvarghid aUniversità di Firenze, Dip. di Chimica, Via della Lastruccia 3 Sesto Fiorentino 50019 Firenze bDipartimento di Ingegneria Civile, Università di Firenze, via S. Marta 3, 50139 Firenze, Italy cTurbocoating S.p.A., via Mistrali 3, 43010 Rubbiano di Solignano, Italy dUniversità degli Studi di Modena e Reggio Emilia, Department of Materials and Environmental Engineering, Via Vignolese 905, 41100 Modena (MO), Italy
Abstract High temperature thermal fatigue causes the failure of Thermal Barrier Coating (TBC) systems. Due to the difference in thickness and microstructure between thick TBCs and traditional thin TBCs, they cannot be assumed a-priori to possess the same failure mechanisms. Thick TBCs, consisting of a CoNiCrAlY bond coat and Yttria Partially Stabilised Zirconia top coat with different degrees of porosity, were produced by Air Plasma Spray. Thermal fatigue resistance limit of TBCs was tested by Furnace Cycling Tests (FCT) according to the specifications of two important Original Equipment Manufacturers (OEMs). TBC systems were analyzed before and after FCT. The morphological and chemical evolution of CoNiCrAlY/TGO microstructure was studied. Sintering effect, residual stress, phase transformation and fracture toughness were evaluated in the ceramic Top Coat. All the tested samples passed FCT according to both OEM specifications. The limit of thermal fatigue resistance increases with the amount of porosity in the Top Coat. The compressive in-plane stresses increase in the TBC systems after thermal cycling, nevertheless the increasing rate has a trend contrary to the porosity level of top coat. The data suggest that the spallation happens at the TGO/Top Coat interface. The failure mechanism of thick TBCs subjected to thermal fatigue is similar to the failure mechanism of thin TBC systems made by APS.
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