ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Gas turbines are critical components in the combined cycle power systems beingdeveloped to generate electricity from solid fuels, such as coal and biomass. The use of such fuelsto produce fuel gases introduces the potential for significant corrosive and erosive damage to gasturbine blades and vanes. Single crystal superalloys have been developed for use with clean fuelsbut are now being deployed in industrial gas turbines. The performance of these materials, withcoatings, has to be determined before they can be used with confidence in dirtier fuel environments.This paper reports results from a series of laboratory tests carried out using the ‘depositreplenishment’ technique to investigate the sensitivity of candidate materials to exposure conditionsanticipated to cause type I hot corrosion in such gas turbines. The materials investigated haveincluded the single crystal nickel-based superalloys CMSX-4 and SC2-B, both bare and with Pt-Alcoatings. The exposure conditions within the laboratory tests have covered ranges of SOx (50 and500 volume parts per million, vpm) and HCl (0 and 500 vpm) in air, as well as 4/1 (Na/K)2SO4deposits, with deposition fluxes of 1.5, 5 and 15 5g/cm2/h, for periods of up to 500 hours at 900°C.Data on the performance of materials has been obtained using dimensional metrology: pre-exposurecontact measurements and post-exposure measurements of features on polished cross-sections.These measurement methods allow distributions of damage data to be determined for use in thedevelopment of materials performance modelling. In addition, the types of damage observed havebeen characterised using standard optical and SEM/EDX techniques.The damage rates of the single crystal materials without coatings are too high for them to be usedwith confidence in gas turbines fired with gases derived from ‘dirty fuels’. Under the more severecombinations of gas composition, deposition flux and metal temperature, the corrosion rates ofthese materials with Pt-Al coatings are also excessive. The data produced from these tests hasallowed the sensitivity of hot corrosion damage to changes in the exposure environment to bedetermined for the single crystal alloys and coating systems examined
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.595-598.689.pdf
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