Oxidation Behaviour of NiCrAl and NiCoCrAl Bond Coatings Under Industrial Gas Turbine Conditions
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Model bond coatings were deposited with a wide range of compositions and their oxidation behaviour investigated at 900 °C. These Ni–Co–Cr–Al coatings were deposited using magnetron sputtering (a physical vapour deposition technique) onto 10 mm diameter sapphire substrates. A range of compositions was generated by co-sputtering from a combination of two or three sources: Ni–10 wt% Cr, Ni–20Cr, Ni–50Cr, Ni–20Co–40Cr and/or Ni–40Co–20Cr combined with pure Al. The coatings were oxidised at 900 °C and the scales formed characterised. These data have been summarised into oxide predominance diagrams to show the relationships between coating compositions and the formation of protective Cr2O3 or Al2O3 scales, or the formation of other, less protective oxides (or mixed oxides). Both coating composition and exposure temperature (by comparison with earlier published research) were found to influence the oxide scale growth rate and oxide type, and thus the resulting degree of protection.
KeywordsBond coat composition TBCs MCrAl Oxidation Oxide predominance diagram
The authors would like to acknowledge the support of The Energy Programme, which is a Research Councils UK cross council initiative led by EPSRC and contributed to by ESRC, NERC, BBSRC and STFC, and specifically the Supergen initiative (Grants GR/S86334/01 and EP/F029748) and the following companies; Alstom Power Ltd., Doosan Babcock, E.ON, National Physical Laboratory, Praxair Surface Technologies Ltd., QinetiQ, Rolls-Royce plc, RWE npower, Siemens Industrial Turbomachinery Ltd. and Tata Steel, for their valuable contributions to the project.
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