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Solid particle erosion of standard and advanced thermal barrier coatings

pubblicazioni - Presentazione

Solid particle erosion of standard and advanced thermal barrier coatings

Sono riassunti e discussi i risultati delle prove di erosione condotte nell’ambito dei progetti Toppcoat e H2IGCC.

The state-of-the-art of the thermal barrier coatings (TBCs), used to protect hot path components from combustion gases, is represented by yttria (partially) stabilized zirconia (YPSZ). Electron beam physical vapour deposition (EB-PVD) coatings have a columnar microstructure that guarantees high strain compliance and better solid particle erosion than PS TBCs. The main drawback of EB-PVD coating is the deposition cost that is higher than that of air plasma sprayed (APS) TBC.

Nowadays segmented APS coatings and PS – PVD have been developed in the frame of the UE TOPPCOAT project to improve solid particle erosion of plasma sprayed TBCs [1,2]. Combustion and cooling technology improvements in combination with higher turbine inlet temperature imply that the standard YSZ approaches certain limitations due to sintering and phase transformations at elevated temperatures.

Moreover under high thermal loading early failure of the coating occurs due to attack by calcium-magnesium-alumino-silicate (CMAS) deposits inducing cracking, spallation and delamination of the coating. Alternative refractory materials development, with higher performances than YSZ, was the objective of the UE project H2IGCC: within this project the erosion resistance of porous, dense segmented YPSZ TBCs and innovative TBCs, featured with a bilayer structure, has been tested at impingement angles of 30° and 90°, representative for particle impingement on trailing and leading edges of gas turbine blades and vanes, respectively [3].

Tests were performed in a solid particle erosion jet tester at high temperatures (700°C and 1000°C) at impingement angles of 30° and 90°, representative for particle impingement on trailing and leading edges of gas turbine blades and vanes, respectively. Microquartz and alumina were chosen as the erodents. To investigate the effect of grain size distribution, erosion rates when fine and coarse alumina powders have been used.

Furthermore, after the end of the tests, the TBC microstructure was investigated using electron microscopy to characterise the failure mechanisms taking place in the TBC. In general TBC with columnar-like microstructures resulted more resistant than standard APS TBCs.

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