C. Giolli, G. Rizzi, Turbocoating SpA, Rubbiano di Solignano, Italy; A. Scrivani, Turbocoating, Rubbiano di Solignano - PR -, Italy; U. Bardi, University of Firenze, Firenze, Italy
Thermal Barrier Coatings consist of a bond coat of MCrAlY alloy (where M means Ni, Co or a combination of both), that can be obtained by Air Plasma Spray, Vacuum Plasma Spray or High Velocity Oxygen Fuel and of a top coat of Yttria Partially Stabilized Zirconia obtained by Air Plasma Spray. These coatings are applied on gas turbine and aeronautical engine components in order to improve their hot corrosion and oxidation resistance and their service life time through a reduction of the service temperature. The main reason of failure of TBC systems is caused, mainly, by high temperature thermal fatigue. This paper addresses the development of thick TBC (with thickness of 1.5 - 2 mm), focusing attention on the microstructure and the porosity of the Yttria Partially Stabilised Zirconia (YPSZ) coating, in relation to its resistance to thermal cycling fatigue. TBC coatings have been produced by means of a NiCoCrAlY as bond coat and YPSZ as top coat, both sprayed by Air Plasma Spray. We characterized the coatings by optical microscopy and hardness measurements. We focused our attention in to analyze the thermal fatigue resistance of new TBC systems and to observe the evolution of the coatings before and after thermal cycling. We performed furnace cycling test (FCT) at different time and temperature on new TBC systems with different porosity. We analyzed the samples before and after FCTs. In order to study their thermal fatigue behavior we used XRD to evaluate the crystallographic evolution of YPSZ and residual stress. We used RAMAN spectroscopy and SEM/EDAX system to study the crystallographic and chemical evolution of the Thermally Grown Oxide (TGO) at the interface BC/TC. We evaluated as porosity influences the thermal fatigue resistance and the mechanism of degradation of porous thick TBC systems.
Summary: Thermal Barrier Coatings consist of a bond coat of MCrAlY alloy (where M means Ni, Co or a combination of both), that can be obtained by Air Plasma Spray, Vacuum Plasma Spray or High Velocity Oxygen Fuel and of a top coat of Yttria Partially Stabilized Zirconia obtained by Air Plasma Spray. These coatings are applied on gas turbine and aeronautical engine components in order to improve their hot corrosion and oxidation resistance and their service life time through a reduction of the service temperature. The main reason of failure of TBC systems is caused, mainly, by high temperature thermal fatigue. This paper addresses the development of thick TBC (with thickness of 1.5 - 2 mm), focusing attention on the microstructure and the porosity of the Yttria Partially Stabilised Zirconia (YPSZ) coating, in relation to its resistance to thermal cycling fatigue. TBC coatings have been produced by means of a NiCoCrAlY as bond coat and YPSZ as top coat, both sprayed by Air Plasma Spray. We characterized the coatings by optical microscopy and hardness measurements. We focused our attention in to analyze the thermal fatigue resistance of new TBC systems and to observe the evolution of the coatings before and after thermal cycling. We performed furnace cycling test (FCT) at different time and temperature on new TBC systems with different porosity. We analyzed the samples before and after FCTs. In order to study their thermal fatigue behavior we used XRD to evaluate the crystallographic evolution of YPSZ and residual stress. We used RAMAN spectroscopy and SEM/EDAX system to study the crystallographic and chemical evolution of the Thermally Grown Oxide (TGO) at the interface BC/TC. We evaluated as porosity influences the thermal fatigue resistance and the mechanism of degradation of porous thick TBC systems.
