High temperature oxidation of MCrAlY-based thermal sprayed bond coats is one of the causes of failure of TBC (Thermal Barrier Coatings) systems: in the last decades extensive investigation was focussed on the improvement of corrosion and oxidation resistance of this class of coatings. In this paper the high temperature oxidation behaviour of NiCoCrAlTaY coatings modified by a PVD surface treatment was evaluated: the coatings, produced by HVOF technique, were protected by an Al2O3-PVD sputtered overlay prior to top coating with YSZ ceramic layer, and were exposed in air at 1100°C up to 400 hours. The oxidation kinetics were evaluated by measuring the thickness of TGO (Thermally Grown Oxide) scale at the several exposure times and the microstructural evolution induced by the heat treatments was invetigated. The effect of the presence of the Al2O3-PVD overlay, in terms of oxidation resistance and microstructural evolution, was assessed by comparing the performance of modified TBCs with unprotected NiCoCrAlTaY systems. The kinetics data showed that the Al2O3-PVD overlay enhances the oxidation resistance of NiCoCrAlTaY coatings and promotes the adhesion between bond and top coat. A thermo-mechanical finite element model of the modified TBC system was also developed: the growth of the oxide scale was modelled and the previously assessed oxidation kinetics were implemented. The finite element analysis allowed to estimate the effects of the PVD film on the mechanical stress field of the TBC system: results showed that the decrease of oxidation rate induced by the PVD oxide film reduces the stress state in the ceramic top coat and at the TGO-YSZ interface, thus potentially improving the durability of the thermal barrier.
High temperature oxidation of MCrAlY coatings modified by Al2O3 PVD overlay / Pulci, Giovanni; Tirillo', Jacopo; Marra, Francesco; Sarasini, Fabrizio; A., Bellucci; Valente, Teodoro; Bartuli, Cecilia. - ELETTRONICO. - (2013). (Intervento presentato al convegno 6th RIPT: Rencontres Internationales sur la Projection Thermique tenutosi a Limoges - France nel 11-13/12/2013).
High temperature oxidation of MCrAlY coatings modified by Al2O3 PVD overlay
PULCI, Giovanni;TIRILLO', Jacopo;MARRA, FRANCESCO;SARASINI, Fabrizio;VALENTE, Teodoro;BARTULI, Cecilia
2013
Abstract
High temperature oxidation of MCrAlY-based thermal sprayed bond coats is one of the causes of failure of TBC (Thermal Barrier Coatings) systems: in the last decades extensive investigation was focussed on the improvement of corrosion and oxidation resistance of this class of coatings. In this paper the high temperature oxidation behaviour of NiCoCrAlTaY coatings modified by a PVD surface treatment was evaluated: the coatings, produced by HVOF technique, were protected by an Al2O3-PVD sputtered overlay prior to top coating with YSZ ceramic layer, and were exposed in air at 1100°C up to 400 hours. The oxidation kinetics were evaluated by measuring the thickness of TGO (Thermally Grown Oxide) scale at the several exposure times and the microstructural evolution induced by the heat treatments was invetigated. The effect of the presence of the Al2O3-PVD overlay, in terms of oxidation resistance and microstructural evolution, was assessed by comparing the performance of modified TBCs with unprotected NiCoCrAlTaY systems. The kinetics data showed that the Al2O3-PVD overlay enhances the oxidation resistance of NiCoCrAlTaY coatings and promotes the adhesion between bond and top coat. A thermo-mechanical finite element model of the modified TBC system was also developed: the growth of the oxide scale was modelled and the previously assessed oxidation kinetics were implemented. The finite element analysis allowed to estimate the effects of the PVD film on the mechanical stress field of the TBC system: results showed that the decrease of oxidation rate induced by the PVD oxide film reduces the stress state in the ceramic top coat and at the TGO-YSZ interface, thus potentially improving the durability of the thermal barrier.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.