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Thermo-physical properties of as deposited and aged state-of-the art and advanced thermal barrier coatings (TBC) for gas turbines

pubblicazioni - Poster

Thermo-physical properties of as deposited and aged state-of-the art and advanced thermal barrier coatings (TBC) for gas turbines

Sono riassunti e discussi i risultati dalla caratterizzazione termofisica di TBC sviluppate nell’ambito del progetto UE H2IGCC.

Ceramic thermal barrier coatings (TBCs) are widely utilised to protect hot path components of gas turbines (GT). Nowadays, the state-of the-art of these TBCs is represented by yttria (partially) stabilized zirconia (YPSZ) (7–8 wt.% Y2O3 + ZrO2) deposited onto the components either by air plasma spray (APS) or by electron beam physical vapour deposition (EB-PVD) [1].

To improve strain compliance and erosion resistance, dense vertically cracked APS TBC have been developed within the last decades. The requirements to operate a GTs at higher temperatures and facing the attack CMAS deposits push towards the development of alternative refractory materials; this was one of the objectives of UE project H2IGCC. This work summarise the main outcomes of the thermo-physical characterisation of state-of-the-art Dense segmented (DS) and highly porous YPSZ, composite YPSZ+Gd2Zr2O7 and Yttrium Aluminium Garnet (YAG) TBCs deposited in double layer architecture by Air Plasma Spray [2].

In particular, thermal diffusivity has been measured for samples aged at different temperatures either in air and in air with 20% steam (the latter atmosphere to simulate the flue gases of a GT fuelled by hydrogen rich syngas) in order to investigate the sintering kinetics of TBCs with different microstructure and chemical compositions. Thermography and Laser Flash measurements have been carried out at different temperatures in the range 25°C – 1100°C. At RT measurements have been carried out in air and in vacuum to non-destructively characterise the pore morphology [3].

The main outcomes of this activity are summarized hereinafter. Thermal diffusivity and conductivity vs. temperature of both porous and dense vertically cracked YPSZ TBC resulted within typical ranges reported in the literature, although a smaller sintering rate is observed, probably caused by the globular shape of most of the pores. No clear evidence of different sintering kinetics caused by the higher steam content has been observed. Thermal diffusivity, conductivity and sintering kinetics of single and double layer composite YPSZ+Gd2Zr2O7 TBCs do not differ significantly from those of YPSZ state-of-the-art TBCs. On the contrary, a significant thermal diffusivity increase (3 times) for YAG TBC samples has been noticed after the heat treatment.

Furthermore, comparing thermal diffusivity as measured in air and in vacuum before and after aging provided useful information on TBC pore morphology evolution as a function of aging. Experimental and modelled values of thermal diffusivity of single and double layer YPSZ-Gd2Zr2O7 are in good agreement.

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