Abstract
Research is being conducted to study the degradation of thermal barrier coatings (TBC) employed on IGCC turbine hot section airfoils due to particulate deposition from contaminants in coal syn-thesis gas (syngas). West Virginia University (WVU) had been working with US Department of Energy, National Energy Technology Laboratory (NETL) to simulate deposition on the pressure side of an IGCC turbine first stage vane. To simulate the contaminant deposition, several TBC coated, angled film-cooled test articles were subjected to accelerated coal fly ash, which was injected into the flow of a combustor facility with a high pressure (approximately 4 atm) and a high temperature (1560 K) environment. To investigate the degradation of the TBCs due to particulate deposition, non-destructive tests were performed using scanning electron microscopy (SEM) evaluation and energy dispersive X-ray spectroscopy (EDS) examinations. The SEM evaluation was used to display the microstructure change within the layers of the TBC system directly related to the fly ash deposition. The SEM micrographs showed that deposition-TBC interaction made the YSZ coating more susceptible to delamination and promoted a dissolution-reprecipitation mechanism that changed the YSZ morphology and composition. The EDS examination provided elemental maps of the shallow infiltration depth of the fly ash and chemical composition spectrum results which showed yttria migration from the YSZ into the deposition.
Highlights
In an effort to improve the efficiency and durability of gas turbines, research and development of thermal barrier coatings (TBC) coating systems are being conducted worldwide
The current study examines the influence of the fly ash deposition on the microstructure of the TBC layers using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS)
Once micro-indentation was completed, SEM micrographs of the top view of the YSZ coatings were taken, and the samples were mounted, polished, and underwent microstructural analysis through scanning electron microscopy (SEM) examinations to provide high resolution images of the cross sections of the samples
Summary
In an effort to improve the efficiency and durability of gas turbines, research and development of TBC coating systems are being conducted worldwide. For the as-deposited TBC coatings, a metallic bond coat (BC) is applied to the super alloy substrate prior to the application of the ceramic top coat This BC coat is responsible for the adhesion between the top coat and the substrate and for providing an aluminum reservoir for the formation of alumina, α-Al2O3, in the thermally grown oxide (TGO). Due to the TBC’s low thermal k relative the substrate, it provides thermal insulation for the gas turbine components, allowing the turbine to operate at much higher gas temperatures than the melting point of the substrate material. This consequentially increases the gas turbine efficiency
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