High-temperature coatings for superalloys can be divided into three categories: Two of them, diffusion and overlay coatings, are both used to protect a system from oxidation and corrosion. The third type, thermal barrier coatings, protects the substrate from thermal degradation. All types of coatings are designed to avoid direct contact between a hot gas or detrimental components from the environment and the base metal alloy. The aim is to enhance the lifetime of high temperature applications,

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... hich is otherwise often limited by corrosion or thermal degradation. In this chapter, the different coatings and their durability are discussed, which ideally matches the aging process of the substrate underneath. Besides the corrosive attack the coatings must also often be able to withstand certain mechanical and thermal mechanical loads as well as erosion. Nevertheless, all coatings have a limited thickness and get consumed in service. Therefore it is essential to understand and choose coatings that show slow degradation mechanisms.