Engineering the interfacial chemistry in metal/oxide systems

Alloys designed for high-temperature applications need to form a protective oxide scale to withstand further degradation by oxidation. The importance of the interfacial chemistry for the adhesion of the protective scale was demonstrated in experiments with β-NiAl, iron-aluminides, NiCrAlYs and Ni-based superalloys. Interfaces between alloys both with and without thermal barrier coatings and their thermally grown alumina scales were studied as well as interfaces between alloys and deposited alumina coatings. It was found, that in all cases improved oxidation performance and scale adhesion could be achieved by doping the alloys with reactive elements. The improvement was shown to be due to interfacial segregation of the reactive element. Segregation of sulfur to internal interfaces on the other hand caused scale spallation.