Gas Turbine Aero-Engine First Stage Turbine Blade Failure Investigation

Plugging material in some of the film cooling channels of a failed aero-gas turbine engine first stage turbine blade is analyzed using the energy dispersive X-ray spectroscopy in an environmental scanning electron microscope. The objective of the analysis was to identify the nature and source of the plugging material that appears to have caused overheating and eventual failure of some of the blades. The results of the analysis indicate that the plugging material, which occurs as a dense aggregate of 0.1 m diameter fibers, is mainly composed of Zr, Y, and O. In addition, the material shows presence of micron size particles dispersed between the fibers. The analysis of the particles indicates they are fluoride-rich compounds, possibly of yttrium or calcium. Small or trace amounts of Ca, Na, and Mg are also observed in the plugging material. The analysis of the areas surrounding the plugged cooling channels shows presence of Cr–Co–Ni–aluminide bond coat and a discontinuous platinum coat over the bond coat. In contrast, the areas surrounding the fractured surface and melted edge show significant presence of calcium fluoride and Mg–Al–silicate. The analysis of melted edge shows presence of all the elements representing various coating layers as well as the impurities; however, Zr and Y were not detected in the melted areas.