The work described in this paper was conducted under Electric Power Research Institute (EPRI) Contract RP 2465, “Rainbow Test of Advanced Coatings for Gas Turbine Blades and Vanes”.

A field test of a rainbow rotor and nozzle was carried out to establish the hot corrosion protection of various aluminide and MCrAlX (X = Y, Hf) overlay coatings on first stage blades and nozzles of a Centaur gas turbine operating in Valera, Venezuela. The blade coatings included both simple and precious metal aluminides, Electron Beam-Physical Vapor Deposition (EB-PVD) coatings and Low Pressure Plasma Spray (LPPS) coatings on Inconel-738LC, Inconel-792 and MAR-M421 substrates. The turbine nozzle vanes were coated by similar methods on FSX-414 and MAR-M509 substrates. Field testing was performed under industrial conditions where the continuous duty engine, used for power generation, ran on a liquid fuel contaminated with sodium and sulfur. The engine test was terminated after nearly 8,000 hours of operation. Visual examination and micro-structural analysis indicated that EB-PVD and LPPS overlay coatings were more effective than simple and modified aluminides for hot section hot corrosion protection. The protection of overlay coatings on nozzle airfoils was found to increase with their chromium content.

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