International audienceImproving sealing between rotating and stationary parts in aerospace gas turbines significantly increases engine performance by improving thermal efficiencies. To reach this aim, abradable seals are being incorporated into turbine casings. With an abradable seal, the blade tips incur into the shroud, thereby reducing the gap between the rotor and the coating to a minimum. These coatings are generally multiphase materials applied by thermal spray techniques and consisting in a combination of metallic matrix and additional dislocator phases with a controlled amount of porosity. The sealing effectiveness requires a combination of properties that are usually optimised empirically with thermal spray coatings generally made up from a range of two-phase powder mixtures. The present study intends to initiate a theoretical approach for the study of these materials aiming at developing a prediction strategy for structure improvement. Image analyses and finite element calculations were used to examine the effect of phase morphology on the mechanical behaviour of two reference abradable systems, namely AlSi-hBN and NiCrAl-Bentonite for compressor stages. Scanning Electronic Microscopy (SEM) was used to obtain a series of micrographs for coating characterisation. These micrographs were then treated to create equivalent images based on geometrical description of the inherent morphology. The resultant reduced images are used to carry out finite element calculations, in order to determine the mechanical properties of each coating. It is believed that this approach provides consistent results and is believed to be a reliable starting point for further coatings design

Metallic honeycombs are widely used in gas turbine engines as inner and outer abradable gas path seals. The ever increasing gas temperatures encountered in the high and low pressure turbine modules of modern engine designs challenge the durability of the thin foil metals used to fabricate seal type honeycomb. In this paper the performance of a number of alloys in turbine seal applications is reviewed. Emphasis is placed on resistance to hot gas corrosion attack and microstructural integrity after exposure to elevated temperatures. The abradability of fabricated seal structures under two distinctly different rub test conditions is reviewed. Among the alloys considered, the Fe-Cr-Al-Y alloy MI 2100 offers a potentially superior combination of oxidation resistance, abradability, fabricability and material cost for seal honeycomb applications.

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This article provides an overview of key thermal spray coatings used in compressors, combustors, and turbine sections of a power-generation gas turbine. It describes the critical components, including combustors, transition ducts, inlet nozzle guide vanes, and first-stage rotating airfoils. Design requirements are reviewed and compared between aerospace and power generation coatings. Application process improvement areas are also discussed as a method of reducing component cost.

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