Operational Experience With Internal Coatings in Aero- and Industrial Gas Turbine Airfoils

Abstract

The internal surfaces of air cooled gas turbine airfoils will oxidize severely during service depending upon operational conditions, chosen design, substrate alloy and the presence of an internal coating. Contradictory experiences by Dutch operators about the need and the performance of internal coatings lead to a research project within the Dutch Gas Turbine Association (VGT). The work focussed on internally coated and non-coated airfoils of civil and military aero engines and industrial gas turbines. Cross-sections from airfoils for metallographic evaluation were selected from the civil aero engines, GE CF6-50 and -80C2 and PW4000, from military engines, PW F100-200 and -220, and from industrial engines, GE Frames 6 and 9. Coating thickness distributions, oxidation resistance and blockage of drilled film cooling holes were reviewed. Particularly the field experiences on the gas turbine airfoils are highlighted in this paper.