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The service of protective coatings at high temperature will lead to interdiffusion between the coating and superalloy. The occurrence of interdiffusion not only reduces the oxidation resistance of the coating but also reduces the mechanical properties of superalloys, especially single crystal superalloys. At present, the main methods of suppressing interdiffusion are: adding a diffusion barrier layer between the coating and superalloy, a so-called "equilibrium" (EQ) coating, and a nanocrystalline coating. In the current review, the advantages and disadvantages of these three methods for suppressing interdiffusion are discussed, and an attempt is made to determine the best method for suppressing interdiffusion to improve the service life of high-temperature components. [ABSTRACT FROM AUTHOR]

Iron aluminide coatings are very resistant to corrosion at 600-700 °C. However, interdiffusion is responsible for a significant reduction of the Al content at the coating surface. A stable diffusion barrier could in principle prevent this degradation mechanism. A new diffusion barrier based on nitrogen was produced and was very effective in reducing coating-substrate interdiffusion on P92. After nitriding P92, an Al slurry was applied and heat-treated, resulting in an overlay coating consisting of an Al solid solution with Cr and Fe. This coating was thinner and quite different from the several Al-Fe intermetallics obtained without nitriding and was fully characterized. A diffusion study was conducted and the results showed that after 2000 h at 650 °C, the new coating suffered very little changes and no interdiffusion with the substrate in contrast with the intermetallic coating deposited without nitriding. Testing under steam and fire-side atmospheres showed promising behavior. [ABSTRACT FROM AUTHOR]