Role of Aluminide coating degradation on Inconel 713 LC used for Compressor Turbines (CT) of Short-haul Aircrafts
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.207
Role of Aluminide coating degradation on Inconel 713 LC used for Compressor Turbines (CT) of Short-haul Aircrafts Joshua K. Ngoret1,2 and Venkata P. Kommula1 1
Department of Mechanical Engineering, University of Botswana, Private Bag 0061, Gaborone.
2
Department of Mechanical Engineering, Jomo Kenyatta University of Agriculture and Technology, 62000-00200, Nairobi, Kenya.
Corresponding author: Email:
[email protected]; Tel: +26776813894/+254726557186
ABSTRACT
This paper investigates the role degradation of protective diffusion aluminide coating on Inconel 713LC used for CT blades of short-haul aircraft fleet played in having the blades prematurely retired from service at 6378 hours, as opposed to their pre-set service time of 10000 hours. The blade samples were subjected to various examinations; X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyse at the; tips, airfoil, as well as the base, transverse and longitudinal, sectioned and unsectioned. As affirmed by both the transverse and longitudinal sections examinations, it was established that thermal attack leading to deterioration of the coating was greater at the tip and airfoils of the blades (the hotter zones) and lesser towards the bases (colder zones). As a result, severe degradation of the core material at the tips and airfoils compared to the bases and more prevalent at the leading edges than trailing edges at the tips. The results further suggest that both active outward Ni diffusion and inward Al diffusion can coexist during exploitation of the blades in service. The study illustrates the role played by the aluminide coating in early failure of CT blades with the aim of bettering the surface coatings and enhancing coating technologies, managing CT blade material monitoring as well as to give insights on advancing CT blades maintenance practices.
Introduction Development, application and evolution of protective surface coatings for hot engine sections dates back to the early 1980s [1]. Aluminides find their use in compressor turbine (CT) blades to improve thermal stress concentration and increase resistance of the material through formation of a continuously growing protective Al2O3 at temperatures over 1000 °C [2-13] to mitigate against damage initiation and
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propagation. Likewise, these coatings increase engines efficiency by allowing higher operational temperatures, protect the core material from attack by chemical constituents in the fuel and the environment in which the engine operates as well as high temperature oxidation and hot corrosion [14-19]. Life cycle of coatings is however limited to between 2000-4000 flight cycles making it cost intensiv
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