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.
Failure mechanism for thermal fatigue of thermal barrier coating systems / C. Giolli, A. Scrivani, G. Rizzi, F. Borgioli, G. Bolelli, L. Lusvarghi. - CD-ROM. - (2008), pp. 1-8. (Intervento presentato al convegno Thermal Spray Crossing Borders, ITSC 2008 International Thermal Spray Conference & Exposition tenutosi a Maastricht (NL) nel 2–4 Giugno 2008).
Failure mechanism for thermal fatigue of thermal barrier coating systems
F. Borgioli;
2008
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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