Rootcause analysis of discoloration of platinum aluminide coated DS CM 247LC high pressure nozzle guide vane of an aero-engine

Detailed metallurgical investigation was carried out on an operating high pressure nozzle guide vane (HPNGV) of an aero-engine to find out the probable reasons for its discoloration and assess its condition for future use. The discoloration intensity on the vane varied from pressure side to suction side and from leading edge to trailing edge. XRD and EDS analysis brought out deposition of iron oxide as the main contributor for discoloration. Cross sectional analysis of the sectioned HPNGV revealed degradation of the platinum modified aluminide coating both compositionally and structurally. Compositional degradation is attributed to high temperature oxidation of the coating. Whereas, structural degradation had multiple reasons, like erosion, Calcium Magnesium Alumino Silicate (CMAS) induced local pitting and internal void formation. Remarkable difference was observed in the structural degradation from pressure side to suction side. Microstructural study of HPNGV base material revealed good phase stability, thereby giving an opportunity for stripping and recoating to extend the life of the component.