Mechanism of adhesion of alumina on MCrAlY alloys

X-ray diffraction has been used to measure stains/ stresses generated in oxide films formed under isothermal conditions at 1150–1225° C and cooled to room temperature. High compressive strains, of the order of 1%, were measured in alumina films formed on FeCrAlY. However, little or no strain was measured in oxide films on NiCrAlY and NiCoCrAlY samples, even when there was no scale spallation. Auger Electron Spectroscopy (AES) experiments have also been conducted to evaluate the role of segregation on scale adhesion. Our studies suggest that the adhesion mechanism might depend on the alloy composition. On iron-based alloys, the scale spallation might be prevented by mechanisms that involve strong bonding at the interface. On the other hand, the scale spallation on nickel-based alloys might be prevented by a mechanism that relieves stresses. Yttrium segregation might help in this process.