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Title:	Wear characteristics of chromium based hard coatings for gas turbine combustor liners
Authors:	Salmi Mohd Yunus @ Abd Wahid (P74529)
Supervisor:	Mariyam Jameelah Ghazali, Dr.
Keywords:	Gas-turbines -- Combustion Gas-turbines Natural gas -- Combustion Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia
Issue Date:	2017
Description:	Chromium (Cr) based coatings offer excellent wear resistance; especially at elevated temperature levels, and incorporate excellent thermal conductivity properties. Applying additives, such as carbon (C) and cobalt (Co) may also improve hardness and delay wear. Therefore, considering these properties, Cr-C and Cr-Co based coating systems were selected to investigate their potential on the mating surfaces of Ni-based superalloy combustor liners of commercial gas turbines that experience temperatures up to 1100 °C. One surface contact on the commercial combustor liner was selected; a fuel nozzle collar, in which was exposed to high temperatures of 350 °C during its operation. In this study, two types of coatings (Cr-61 % Co and Cr-13 % C) were deposited onto nickel-based substrates via air plasma spray to investigate their wear resistance characteristics at elevated temperatures. The air plasma spray technique was chosen due to the high deposition rate for ceramic coating feedstock. This results in the minimum waste of feedstock powders during deposition, therefore improving the bond strength of the coating system. All coatings were applied with an average thickness of 100 ± 25 μm. It was found that the deposited Cr-C coatings exhibited uniform microstructures with only a small amount of porosity. Also, having 17 % greater hardness and 30 % lower surface roughness than that of Cr-Co coatings. This was because of high thermal conductivity that improved the surface roughness and cohesion strength of the coating system. The considerable hardness of the Cr-C coating was not only attributed to the higher hardness of C-content but was also caused by high oxidation forming during the deposition process. The irregular shapes of the Cr-C feedstock powders also played a major role in producing a higher specific area than the spherical shaped Cr-Co feedstock. This contributed to higher oxidation in the coating system. An accelerated wear test was conducted at three different operating temperatures; at room temperature (25 °C), 100 °C and 200 °C to determine the wear characteristics at elevated temperatures. For Cr-Co coating, the hardness decreased with increasing temperatures, whereas the worn Cr-C surfaces exhibited an improvement in hardness with greater stability after reaching 100 °C. It was found that the wear mechanism of Cr-C and Cr-Co coated Ni alloys were primarily abrasive with high severity in volume loss by Cr-Co coatings. In summary, Cr-C coated Ni alloy was found to be much better than the Cr-Co based coating to delay the wear in gas turbines. This was also qualitatively predicted to support the overall finding that Cr-C hard coating should be used to extend operating hours for a further 4,000 hours, therefore, resulting in 12,000 total hours instead of the current 8,000 hours.,“Certification of Master's/Doctoral Thesis” is not available,Master of Science
Pages:	84
Call Number:	TJ778.S238 2017 3 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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