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Solid particle erosion of standard and advanced thermal barrier coatings

pubblicazioni - Articolo

Solid particle erosion of standard and advanced thermal barrier coatings

Nell’ambito del progetto europeo H2IGCC sono state sviluppate barriere termiche di tipo innovativo caratterizzate da una struttura a doppio strato, alternative alle TBC di Zirconia parzialmente stabilizzata con Yttrio che rappresentano lo stato dell’arte per impieghi in parti calde di turbine a gas.Tali TBC innovative sono state testate ad erosione in condizioni rappresentative dell’esercizio e poste a confronto con TBC standard di tipo poroso e segmentato. In generale, è stata osservata una migliore resistenza all’erosione delle TBC segmentate indipendentemente dalle condizioni sperimentali, mentre uno dei rivestimenti innovativi a doppio strato, grazie alla sua peculiare micro-struttura, ha mostrato una resistenza all’erosione molto interessante, almeno nel caso di particelle fini di erosivo.

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). 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. Alumina powders with grain size representative of sand and fly ashes, respectively were chosen as the erodent.

A better erosion resistance of dense segmented TBCs regardless of experimental conditions were observed, whereas one of the new bilayer coating, due to its peculiar micro-structure, showed a very interesting erosion resistance, at least with fine erosion particles.

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