High-temperature corrosion of alumina-forming coatings for superalloys

Abstract The results of recent experiments on the cyclic oxidation and hot corrosion of diffusion aluminide and CoCrAlY overlay coatings on nickel-base superalloys are described. It is shown that platinum additions to aluminide coatings produce a substantial increase in resistance to cyclic oxidation and high temperature (Type 1) hot corrosion but have a rather small effect on resistance to low-temperature (Type 2) hot corrosion. The corrosion of aluminide coatings is also shown to be influenced by the composition of the underlying superalloy. Mechanisms for the above behavior are proposed. The effects of yttrium and hafnium on the cyclic oxidation of CoCrAl are illustrated. The results of scanning and transmission electron microscope characterization of the hot corrosion morphologies of CoCrAlY coatings are discussed and a mechanism to account for the microstructures is briefly described.