Cerca nel sito per parola chiave

pubblicazioni - Presentazione

Thermal diffusivity measurements as a non destructive tool for the microstructural characterisation and the integrity assessment of thermal barrier coatings

pubblicazioni - Presentazione

Thermal diffusivity measurements as a non destructive tool for the microstructural characterisation and the integrity assessment of thermal barrier coatings

Nell’intervento è fornita una panoramica delle attività di ricerca che utilizzando tecniche termografiche e/o foto-termiche per la misura della diffusività termica hanno consentito di effettuare la caratterizzazione micro strutturale e la valutazione dello stato d’integrità di rivestimenti ceramici con funzione di barriera termica utilizzati per proteggere le parti calde delle turbine a gas.

For thin (less than 200 micron) air plasma spray (APS) and electron beam physical vapor deposition (EBPVD) ceramic thermal barrier coatings (TBCs) used to protect gas turbine hot path, some non-destructive techniques indicate damage at the bond coat-TBC interface during either ageing or cyclic oxidation tests. However, no technique is available for thick (more than 250 micron) APS TBCs. A semi-quantitative estimation of cracks at the interface of TBCs is obtained from thermal diffusivity values measured on coupons subjected to thermal cycling by using a single side thermographic technique. In fact, during thermal cycling, two phenomena occur: sintering that promotes a significant increase of thermal diffusivity, and cracking that, representing an additional thermal resistance, causes an apparent decrease of thermal diffusivity. For each sample, the thermal diffusivity was measured at fixed lifetimes and the evolution of the cracked fraction of the interface was estimated by adopting a 2-D inversion model. Furthermore, at each of the six lifetime fractions some samples were destructively characterised by image analysis and the results were compared to the estimations given by the inversion model. The microstructure of as sprayed and sintered freestanding APS YPSZ TBC samples has been characterized by measuring thermal diffusivity after filling pores with different gases, by using Hg porosimetry and IA and results have been compared; furthermore, the microstructure and thermal diffusivity of sintered samples have been compared with the sintering forecasts furnished by the Cipitria’s sintering code coupled with the Bruggeman model for thermal diffusivity estimation.

Progetti

Commenti